Left-handed sugar
Andrew Lewis Tepper
mirror image of sugrose/glucose/fructose/etc at the molecular level.
Enzymes can't break it down; it's 0-calorie. There was (is?) a company
in the US (Chicago I think) working on producing it cheeply. I spoke to
someone at the company at the time, and he said that the cost to produce
used to be $30,000 per gram, but had come down. They were trying to get
the price low enough to compete with other artificial sweeteners.
Has anyone heard news of this since then? It was claimed that it would
be the ultimate artificial sweetener since it would have no aftertaste,
could be used in cooking/candy, etc.
Andy
Mark Robert Thorson
Anthony Datri
As I understand it, mannitol and sorbitol are such. I've never quite figured
out why they aren't used more.
--
======================================================================8--<
la1...@albnyvms.bitnet
Clover, who read the warning on the back of the sorbitol-candy iin the
health food store and put it back.
Andrew Lewis Tepper
by Anthony Da...@siemens.co
>
> As I understand it, mannitol and sorbitol are such. I've never quite figured
> out why they aren't used more.
don't. (Of course they have calories, but the enzymes we have don't fit
left-handed sugars.
Another interesting thing about left handed sugars is that they are
found in nature in only three places: Flax Seed, Blue-Green algae, and
the berries of Mountain Ash trees.
Andy
Mark Robert Thorson
having a discussion in rec.food.cooking about the supposed existence
of left-handed sugars which are indigestible hence calorie-free.
I contend that if L-sugars were calorie-free, they probably wouldn't
be sweet, either. Can someone in the sci groups clarify this?
David Degraw
In article <72...@cup.portal.com>, m...@cup.portal.com (Mark Robert Thorson)
writes:
By L-sugar, I suppose you mean the levorotatory variety of an enantiomer.
Common table sugar is sucrose, an enatiomeric molecule. The stuff
we eat is a racemic (50%-50%) mixure of R and L sucrose. It may be
possible to isolate L-sucrose by using a *certain* microorganism which
can metabolize only R-sucrose. A technique I read about to isolate
alpha-L-glucose used a microorganism (I don't have the refernce for which
kind) which selectively metabolized alpha-R-glucose.
I cannot tell you which enantiomer of sucrose actually reacts with human
taste receptors.
Both R and L sucrose should be digestible since only a fraction of human
digestion is carried out by bacteria. Most of the digestion of
sucrose occurs in the small intestine where it is lysed by sucrase into
glucose and fructose. Glucose and fructose are then transported to the
liver for storage via the intestinal capillaries. Although most of the
bacteria live in the small intestine, they seem to play a small role in
sucrose digestion
Mark Robert Thorson
Not necessarily. I am referring to the D- and L- system used by sugar
chemists. There are three systems for describing molecules with
handedness (i.e., chiral molecules). Dextrorotatory vs. levorotatory
molecules are described by the r- and l- system. The R- and S- system
(called "big R" and "big S") refers to the molecular weights of the
stuff attached to a carbon atom which has four different things attached
to it (i.e., a chiral center).
The D- and L- system is very complex, requiring the assignment of D vs. L
by deriving a synthesis for that molecule from glyceraldeyde. Certain
scientists, especially sugar chemists, prefer the D- and L- system because
all the biologically important amino acids are L and all the sugars are D.
(There are a few exceptions.) Generally speaking, there is no conversion
between D and L, so the $64 question is whether molecules like L-glucose
and L-fructose would be sweet-tasting calorie-free substitutes for sugar.
I'm skeptical, because if these molecules can't be digested, it seems
even more likely to me they can't be tasted. If the highly reactive
conditions in the stomach, intestines, liver, etc. can't touch these
molecules, then how are they going to fit into the even more discriminating
active site of a taste receptor surface protein? I just can't see how
that would be possible, but I'm willing to admit I don't know.
(nb: a molecule can simultaneously be little r, big S, and big D, or any
other combination; none of these systems has predictive value in
determining the classification of a molecule under the other two systems.)
Mark Robert Thorson
little l), I meant d- and l- (little d and little l). I suppose I may
have made other errors, too. I don't think about this stuff more than
about once per year.
RAGIN CAJUN
Also, it still raises the blood sugar level it only does it slower.
Alma
David Toland
Fructose (fruit sugar) is the levorotatory form of dextrose. It is
both sweet and digestible. It is true that d- and l- forms of chems
will react to form different products with other chiral (assymmetric)
compounds, but the various sugars seem to be digestible nonetheless.
I'm not a biochemist, just a (former) organic and electrochemist.
Perhaps achiral reactions break down the sugars to achiral components,
or perhaps there is more than one respiratory process involved. Could
a biochemist out there clarify further?
--
--------------------------------------------------------------------------
All opinions are MINE MINE MINE, and not necessarily anyone else's.
d...@phlan.sw.stratus.com | "Laddie, you'll be needin' something to wash
| that doon with."
Herman Rubin
>In article <72...@cup.portal.com> m...@cup.portal.com (Mark Robert Thorson) writes:
>>Please excuse the cross-posting into the sci newsgroups, but we've been
>>having a discussion in rec.food.cooking about the supposed existence
>>of left-handed sugars which are indigestible hence calorie-free.
>>I contend that if L-sugars were calorie-free, they probably wouldn't
>>be sweet, either. Can someone in the sci groups clarify this?
>Fructose (fruit sugar) is the levorotatory form of dextrose. It is
>both sweet and digestible. It is true that d- and l- forms of chems
>will react to form different products with other chiral (assymmetric)
>compounds, but the various sugars seem to be digestible nonetheless.
This is totally false. The compounds have the same gross chemical
composition, but they are not forms of each other.
--
Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907-1399
Phone: (317)494-6054
hru...@snap.stat.purdue.edu (Internet, bitnet)
{purdue,pur-ee}!snap.stat!hrubin(UUCP)
Paul S. Winalski
In article <72...@cup.portal.com>,
Sugar biochemistry 101:
Sugars are compounds of the general form (CH2O)n where n>=3. They are
poly-alcohols with unbranched carbon skeletons and a -OH group on all but one
of the carbons. That carbon has a C=O double bond. The double-bonded carbon
is either the terminal carbon of the chain or the penultimate carbon. If it
is the terminal carbon, the sugar is also an aldehyde and is referred to as
an aldose. If it is the penultimate carbon, the sugar is also a ketone and is
referred to as a ketose. Sugars are also classed based on the number of
carbons in the molecole as trioses (3 carbons), tetroses (4 carbons), pentoses
(5 carbons), hexoses (6 carbons), etc. For example, glucose is an aldohexose
(6 carbons, double bond on a terminal carbon). Fructose is a ketohexose
(6 carbons, double bond on the penultimate carbon).
In aqueous solution, the aldehyde or ketone group can react with the hydroxide
at the other terminus to form a ring with an ether (C-O-C) linkage. Such rings
are 6-membered for aldoses and 5-membered for ketoses. This is in fact the
normal configuration for such sugars in solution and in the body. Sugars can
also form ether linkages with other sugar molecules to form polymers known as
polysaccharides. The simplest polysaccharides contain two sugar molecules
linked together and are called disaccharides. Examples are sucrose [table
sugar] (glucose + fructose), maltose [barley sugar] (glucose + glucose),
and lactose [milk sugar] (glucose + galactose). Long-chain polysaccharides
include the starches, glycogens, and celluloses.
Now we come to stereochemistry. The three-carbon aldose, glyceraldehyde, has
one asymmetric carbon. It therefore exists in two isomeric forms, its
crystals are asymmetric, and therefore they will rotate polarized light. The
two forms are named D-glyceraldehyde and L-glyceraldehyde. The D (dextro-)
form rotates light to the right and the L (levo-) form rotates polarized light
to the left. The four-carbon aldoses have two asymmetric carbon atoms, and
so they exist in four isomeric forms, two of which are mirror images of
the other two. Likewise there are a total of eight aldopentoses (in four pairs
of mirror images) and 16 aldohexoses (in eight pairs of mirror images).
Each isomer that differs at a carbon other than the penultimate one has a
unique name. The penultimate carbon is used to give the compound a D- or L-
prefix, based on how that carbon matches up with the asymmetric carbon of
D- or L-glyceraldehyde. Note that for sugars other than glyceraldehyde, there
is no relationship between the D- or L- prefix and how the sugar rotates
polarized light. D- and L- refer to the configuration about the penultimate
carbon atom. Thus, we have D-glucose and L-glucose, which are mirror images
of each other, likewise D-galactose and L-galactose, etc. Glucose and galactose
are isomers that differ from each other by the configuration about one of the
asymmetric carbons (but not the penultimate one).
The situation is similar for the ketoses. Dihydroxyacetone, the 3-carbon
ketone, is a symmetric molecule and so exists in only one isomeric form.
The ketotetroses have one asymmetric center, and thus there are two isomers,
designated D- and L-, once again based on the configuration of the first
asymmetric carbon atom in relationship to glyceraldehyde. There are four
isomers of the ketopentoses, in two mirror-image pairs, and eight isomers of
the ketohexoses, in four mirror-image pairs. Once again, the D- or L- prefix
has nothing to do with how polarized light is rotated. D-fructose rotates
polarized light to the left, which is how it gets its common name, levulose.
It turns out that nearly all of the simple sugars commonly found in nature are
D-isomers. Levulose is D-fructose.
Cells contain a wide variety of enzymes that can convert one isomeric form
of a sugar to another (isomerases), split a sugar into two sugars, or merge two
simple sugars into a longer sugar (transaldolase, transketolase). The end
result of this is that all of the simple sugars, regardless of isomeric form,
can be converted into D-glucose, the form that is burned in the main catabolic
pathway for sugars to produce energy.
So the L-sugars *are* metabolizable, albeit more slowly than D-glucose, which
is the isomer that most organisms prefer.
Now there is one more wrinkle to this. When a hexose forms a ring, that
causes one more carbon atom to be asymmetric. In their ring forms, these
sugars thus have twice as many isomers. These are classified as a- (alpha)
or b- (beta), based on their configuration about this new center of asymmetry.
The alpha forms are the ones that are metabolizable. The alpha and beta forms
readily interconvert in solution, so they are not an issue in metabolism of
simple sugars. However, when sugars are linked to form polysaccharides, whether
the linkage is in alpha- or beta- configuration is critical, since most enzymes
will accept only one of the configurations. For example, maltose is a
glucose-glucose polysaccharide with the linkage in alpha configuration. If the
linkage is beta, you have cellobiose, not maltose. Likewise, long-chain
glucose polymers with the linkages in alpha configuration are starches, which
are readily digestible. If the linkages are in beta configuration, you have
cellulose, not starch, which is not digestible. Only a few kinds of bacteria
and protozoans have the proper enzymes for breaking beta linkages in
polysaccharides.
Regarding sweetness, all (or nearly all, anyway) of the simple sugars taste
sweet. Among the polysaccharides, the long-chain compounds (starch, glycogen,
cellulose) do not have a sweet taste. Certainly some of the disaccharides do
(sucrose, maltose, galactose), although I'm not sure whether this is due to
their being intrinsically sweet or if it's because they are readily broken down
to simple sugars by enzymes in saliva.
So the bottom line is, L-sugars are digestible, albeit not as readily as their
D- counterparts, and they do taste sweet. On the other hand, disaccharides
with a beta linkage are not digestible, which is why humans cannot survive on
a diet of leaves or wood. Cellobiose, the beta-1-6-D-glucose disaccharide,
is not digestible, but I don't think it tastes sweet, either.
In any event, since the L-isomer sugars are fairly rare in nature, dietary
sweeteners based on them would likely be prohibitively expensive.
--PSW
Richard Chycoski
wina...@adserv.enet.dec.com (Paul S. Winalski) writes:
>
> Sugar biochemistry 101:
>
.. and there follows a lot of *very* interesting stuff that I have now
archived for later digestion! Thank you, Paul!
Earlier someone suggested that Sorbitol and Mannitol were useful non-caloric
replacements for sugar. As I understand it, Sorbitol is the one of the
substances produced by the body when you start "burning muscle" after you've
consumed to more readily available resources during a workout. (I'm neither
a chemist nor a biochemist, so I'm willing to stand corrected if necessary!)
Sorbitol is therfore caloric, and readily aborbed by the body. I can confirm
this, since I know of diabetics that have cannot tolerate Sorbitol, since
the resulting blood sugar rise is indistinguishable from foods containing
the more usual sugars. I am hypoglycaemic, and experience similar reactions.
However, where does 'Sucralose', the sweetner found in 'Splenda', come in?
Is it just a very sweet sugar, since only about a half a milligram is present
in a teaspoon-sugar-equivalent sample? I hope that nasty side effects are not
discovered with this substance, since this is the first year in many that I've
been able to enjoy a number of baked Christmas treats!
- Richard Chycoski
Academic Computing Services
Simon Fraser University
Richard Sucgang
>Fructose (fruit sugar) is the levorotatory form of dextrose. It is
>both sweet and digestible. It is true that d- and l- forms of chems
I won't be the only one reacting to this but: NO NO NO NO!
When sucrose (that's table sugar) is cleaved into its component
monosaccharides, you get two sugars that each rotate light in right
(dextrose) and left ways (fructose or invert sugar). What people are
talking about here is the true L-dextrose, I believe, which is not the way
light is rotated, but the way the atoms are arranged as a mirror image.
>I'm not a biochemist, just a (former) organic and electrochemist.
T'sokay. :)
-rich
Richard Sucgang : Dept. of Anatomy and Cell Biology Columbia University
(suc...@cuhhca.hhmi.columbia.edu | rs...@cunixf.cc.columbia.edu)
"...Dr. Jekyll and Mr. Hyde, individually, collectively or otherwise."
Peggy Shambo
>If such a product existed, it wouldn't taste sweet, would it?
Yes, it does exist.
Yes, it is sweet (this is only hearsay, I have never tasted it myself)
Jazzie
>>>MATRIX version 1.20g
David Toland
>In article <1hklpg...@transfer.stratus.com> d...@bigbootay.sw.stratus.com (David Toland) writes:
>>Fructose (fruit sugar) is the levorotatory form of dextrose. It is
>>both sweet and digestible. It is true that d- and l- forms of chems
>
>I won't be the only one reacting to this but: NO NO NO NO!
<<Much egg on face...>>
You're right of course. I've mixed up my sugars badly (I guess you
know what I *didn't* work on :-)).
Just a random thought. Wouldn't it be nasty if the stereoisomer of one
of the common sugars turned out to be pharmacologically potent?
Cathy Smith
I used it, alot of the rice stuck to the bottom. I tried again using
a little more water and spraying the pan with Pam but there was still
rice stuck to the bottom. The pan itself is made of aluminum so I
thought that might be the problem but I looked at a higher priced
"Rival" brand model and it was made of the same thing. I live in
Boulder (5400') which might have something to do with it but I'm
not sure. Does anyone have any suggestions?
Cathy Smith
c...@noaacrd.colorado.edu
Paul S. Winalski
In an earlier posting, I said that the linkage in sucrose was alpha 1->6.
I am sure about the alpha part, but it might be a 1->4 glycosidic linkage, not
1->6. Unfortunately, my biochemistry textbook is at home.
--PSW
Paul S. Winalski
In article <1992Dec27.1...@lclark.edu>,
deg...@lclark.edu (David Degraw) writes:
|>
|>By L-sugar, I suppose you mean the levorotatory variety of an enantiomer.
|>Common table sugar is sucrose, an enatiomeric molecule. The stuff
|>we eat is a racemic (50%-50%) mixure of R and L sucrose.
Common table sugar is in fact entirely alpha-D-glucose linked by a 1-6
ether bridge in alpha configuration to alpha-D-fructose. It is NOT a racemic
mixture. Enzymes are extremely picky about which enantiomer of a molecule they
will accept, and the plants that are sources for table sugar only synthesize
the alpha-D-glucose-(1->6)-D-fructose enantiomer.
|> It may be
|>possible to isolate L-sucrose by using a *certain* microorganism which
|>can metabolize only R-sucrose. A technique I read about to isolate
|>alpha-L-glucose used a microorganism (I don't have the refernce for which
|>kind) which selectively metabolized alpha-R-glucose.
That would have to be a bacterium lacking the enzyme that performs general
alpha-linkage cleavage of disaccharides, but posessing the enzyme that
specifically cleaves alpha-D-glucose-(1->6)-D-fructose (aka D-sucrose).
|>I cannot tell you which enantiomer of sucrose actually reacts with human
|>taste receptors.
I think they both do.
|>Both R and L sucrose should be digestible since only a fraction of human
|>digestion is carried out by bacteria. Most of the digestion of
|>sucrose occurs in the small intestine where it is lysed by sucrase into
|>glucose and fructose.
There are bunch of other disaccharide lyases, some of which are stereospecific
for particular simple sugar isomers (e.g., lactase), and some of which are not.
The more general-purpose ones act much more slowly than the specific enzymes.
All of them demand the alpha enantiomeric form of the glycosidic linkage.
|> Glucose and fructose are then transported to the
|>liver for storage via the intestinal capillaries. Although most of the
|>bacteria live in the small intestine, they seem to play a small role in
|>sucrose digestion
|>
Although they play a big role in lactose indigestion, and anybody with lactose
intolerance (lack of the enzyme lactase) can attest.
--PSW
Paul S. Winalski
In article <72...@cup.portal.com>,
|>by deriving a synthesis for that molecule from glyceraldeyde.
The D- and L- convention is based on the configuration about the anomeric
carbon adjacent in the chain to the aldo- or keto-carbon.
|> Certain
|>scientists, especially sugar chemists, prefer the D- and L- system because
|>all the biologically important amino acids are L and all the sugars are D.
|>(There are a few exceptions.) Generally speaking, there is no conversion
|>between D and L, so the $64 question is whether molecules like L-glucose
|>and L-fructose would be sweet-tasting calorie-free substitutes for sugar.
I believe that L- forms can be interconverted to D- forms, albeit not
particularly readily, and it might require attachment of an additional phosphate
(at the expense of ATP) to do so. If I recall, in higher organisms, the liver
posesses an enzyme that will rotate the configuration at the carbon adjacent
to the aldehyde carbon of aldoses. I think it catalyzes the reaction
L-aldose<->cis-enediol<->ketose<->trans-enediol<->D-aldose. Once the sugar is
in D-form, there's a whole series of enzymes that interconvert the various
isomers, and so you can eventually get D-glucose from L-glucose.
|>I'm skeptical, because if these molecules can't be digested, it seems
|>even more likely to me they can't be tasted. If the highly reactive
|>conditions in the stomach, intestines, liver, etc. can't touch these
|>molecules, then how are they going to fit into the even more discriminating
|>active site of a taste receptor surface protein? I just can't see how
|>that would be possible, but I'm willing to admit I don't know.
It depends on what the receptor is set up to detect. The "sweet" receptors
seem to be relatively nonspecific. They trigger on all (or nearly all--it's
always dangerous to say "all" in Biology) simple sugars in D-configuration,
but they also trigger on things like dihydroxyacetone, which is a symmetric
molecule, and glycerol, some amino acids, aspartame, cyclamates, and
saccharin, which aren't even sugars at all. I think all you need is a
sufficient number of -OH groups in close proximity on aliphatic carbons to
trigger the "sweet" sensation. L-sugars only differ from their D-counterparts
(which demonstrably taste sweet) by configuration about one carbon atom. I
don't think that's important to the receptors.
--PSW
Clover M.
whick brand(s) would be the easiest to cook non-white rice in, i.e.
red rice, wild rice (yes, I know it's not REALLY rice), "sweet" rice,
sticky rice, etc, etc. Also, I need to buy one that can cook other
grains - wheat, barley, quinoa, etc, etc.
Clover
la1...@albnyvms.bitnet
Clover
la1...@albnyvms.bitnet
This is my very first sig.file
Patt Bromberger
>Hi- I recently bought a rice cooker (Singer brand) and the first time
>I used it, alot of the rice stuck to the bottom. I tried again using
>not sure. Does anyone have any suggestions?
Perfectly normal for any rice cooker - you left the rice sitting in
there right after it was cooked, right?
I found that if i use my oven mitts and gently lift out the aluminum
"tub" full of HOT rice and then use my rubber spatula all around and
under the rice to transfer it to a bowl then hardly any rice sticks to
the aluminum tub; but then, the rice doesn't stay warm in the bowl :-(
Leave your rice in the rice cooker and when you're all finished with
the rice you wanted to eat and have put away the leftovers, just soak
the aluminum tub in hot, soapy water overnight and rinse it out in the
morning - everything comes out clean and tidy!
>
>
>
>
>--
>c...@noaacrd.colorado.edu
--
Patricia Ann Bromberger pa...@panix.com
This quote borrowed from: Gary.Pe...@f12.n2610.z1.fidonet.org
... "It matters not so much what you sing, but why..." J.S. Bach
Dale Tanigawa
>>Please excuse the cross-posting into the sci newsgroups, but we've been
>>having a discussion in rec.food.cooking about the supposed existence
>>of left-handed sugars which are indigestible hence calorie-free.
>>I contend that if L-sugars were calorie-free, they probably wouldn't
>>be sweet, either. Can someone in the sci groups clarify this?
>
>Fructose (fruit sugar) is the levorotatory form of dextrose. It is
>both sweet and digestible. It is true that d- and l- forms of chems
>will react to form different products with other chiral (assymmetric)
>compounds, but the various sugars seem to be digestible nonetheless.
>
>I'm not a biochemist, just a (former) organic and electrochemist.
>Perhaps achiral reactions break down the sugars to achiral components,
>or perhaps there is more than one respiratory process involved. Could
>a biochemist out there clarify further?
Except for a very few exceptions in a very few species, all biologically
active sugars are D- sugars. Fructose can be made D- or L- form, and the
fructose referred to as fruit sugar is the D- form in biochemistry. I
don't know if organic chemistry uses different nomenclature, but it appears
it might be so. Another poster stated that common sugar is a 50-50 blend
of d- and l- sugars in a racemic mixture. I think this poster may actually
be referring to the alpha- and beta- internal hemiacetals that many sugars
form in solution, rapidly interconverting between the two configurations.
Sugars do not interconvert between D- and L- forms like this. All the
sugar that you are likely to ever eat is a D- sugar.
L- sugars are indigestible since the chiral molecule doesn't fit into the
enzymes in your body and there is no provision for turning an L- sugar
into a D- sugar. Whether it would taste sweet I don't know, it's not
my field of interest. L- sugars are a bad replacement for D- sugars for
several reasons. If a particular L- sugar were incapable of being absorbed
in the intestine, anybody eating it would suffer the same symptoms as a
lactose-intolerant person. The sugar would osmotically "pull" water into
the intestine, causing bloating, pain, and diarrhea. If the sugar were
able to pass into the bloodstream, it would likely poison the eater. In
sufficient concentration, sugar is a poison, which is why your body packages
it away in a non-harmful form as soon as it can and parcels it out as you
need it. Sugar is a common method of preservation in the kitchen---its
preservative effect is why fruits are packed in syrup---no bug could survive
such a high sugar concentration. Your body would be unable to regulate the
blood level of L- sugars because it has no mechanisms for dealing with them.
I can see where the confusion arises---someone looking at a biochemical
sugar chart would be likely to assume that mannose and sorbose are L- sugars
because they are stereochemically related to glucose and fructose.
Biochemists often leave the D- part off, because it is commonly understood
that it belongs. Many of the "lesser" sugars, such as mannose and sorbose
are useful for diabetics because they aren't glucose, and they decrease the
available calories because the body's machinery for getting energy from
these sugars is a lot less efficient than the widely-used glucose method.
Not to mention that any recipe that relied on yeast and sugar for rising
would never be able to use L- sugars either. Yeast can't digest them any
David Degraw
wina...@adserv.enet.dec.com (Paul S. Winalski) in,
Message-ID: <1992Dec27.2...@nntpd2.cxo.dec.com>
Article-I.D.: nntpd2.1992Dec27.212634.25439 writes,
>>deg...@lclark.edu (David Degraw) writes:
>>|>
>>|>By L-sugar, I suppose you mean the levorotatory variety of an enantiomer.
>>|>Common table sugar is sucrose, an enatiomeric molecule. The stuff
>>|>we eat is a racemic (50%-50%) mixure of R and L sucrose.
>>
>>Common table sugar is in fact entirely alpha-D-glucose linked by a 1-6
>>ether bridge in alpha configuration to alpha-D-fructose. It is NOT a racemic
>>mixture. Enzymes are extremely picky about which enantiomer of a molecule they
>>will accept, and the plants that are sources for table sugar only synthesize
>>the alpha-D-glucose-(1->6)-D-fructose enantiomer.
>>
>>|> It may be
>>|>possible to isolate L-sucrose by using a *certain* microorganism which
>>|>can metabolize only R-sucrose. A technique I read about to isolate
>>|>alpha-L-glucose used a microorganism (I don't have the refernce for which
>>|>kind) which selectively metabolized alpha-R-glucose.
>>
>>That would have to be a bacterium lacking the enzyme that performs general
>>alpha-linkage cleavage of disaccharides, but posessing the enzyme that
>>specifically cleaves alpha-D-glucose-(1->6)-D-fructose (aka D-sucrose).
(rest of post deleted)
In a reference book, sucrose is shown as a disaccharide comprised of
alpha-D-glucose ether bridged to D-sucrose. The bridge is a 1->2 ether
bridge involving the 1-carbon on the glucose and the 2-carbon on the
fructose.
I imagine a bacterium lacking a general-purpose alpha-lysing enzyme
could not metabolize *any* sort of disaccharide (maybe beta-disachs?).
Is should be common knowledge that many bacterium can metabolize glucose
made along biosynthetic pathways. (i.e. bacterial have no trouble
metabolizing naturally-occuring alpha-D-glucose)
In a lab where synthetic forms of glucose are available, one might
wonder if the same bacteria can consume other configurational
stereoisomers of glucose.
I have only heard that *certain* bacteria are able to distinguish
D-glucose from L-glucose. However, I have no idea whether there
exist species which can tell apart alpha from beta.
Next post I'll be more specific and definitive.
BTW Are there alpha and beta varieties of sucrose also?
-Dave
David E. Scheim
>Except for a very few exceptions in a very few species, all biologically
>active sugars are D- sugars. Fructose can be made D- or L- form, and the
>fructose referred to as fruit sugar is the D- form in biochemistry. I
>don't know if organic chemistry uses different nomenclature, but it appears
>it might be so. Another poster stated that common sugar is a 50-50 blend
>of d- and l- sugars in a racemic mixture. I think this poster may actually
>be referring to the alpha- and beta- internal hemiacetals that many sugars
>form in solution, rapidly interconverting between the two configurations.
>Sugars do not interconvert between D- and L- forms like this. All the
>sugar that you are likely to ever eat is a D- sugar.
I've seen a variety of statements and nomenclatures used when discussing the
various isomers of sugars, which, given my limited knowledge of chemistry,
has made clarity elusive for me. Now that this thread seems to be resolving
this matter, I'd like to try to get a definitve answer on one question.
Various drug protocols in Europe specify infusion of glucose, while similar
protocols in the United States usually specify dextrose. I've been assured
that powdered dextrose in solution equilibrates into glucose solution, but I
would appreciate confirmation and perhaps some clarification, as well as
some idea as to how long such equilibration takes.
Also, I just read a paper on the transport of sugars in various malignant
and normal cells which reported, I believe, that L-glucose would penetrate
only the malignant cells. It is indeed well established that glucose
transport and metabolism is sharply abnormal in cancer cells. This lead me
to wonder if certain cytotoxic compounds bound to L-glucose might
provide a potential approach to cancer treatment? Any comments?
/*********************************************************************/
/* --- David E. Scheim --- */
/* BITNET: DES@NIHNEI31 */
/* INTERNET: de...@helix.nih.gov PHONE: 301 496-2194 */
/* CompuServe: 73750,3305 FAX: 301 402-1065 */
/* */
/* DISCLAIMER: These comments are offered to share knowledge based */
/* upon my personal views. They do not represent the positions */
/* of my employer. */
/*********************************************************************/
The Gecko
>carbon adjacent in the chain to the aldo- or keto-carbon.
The convention places the D(L) carbon farthest from the aldo or
keto carbon. The anomeric carbon is not the D(L) carbon, but the carbon
which in the open chain *was* the aldo or keto carbon, and which in the
pyranose or furanose ring is a (hemi)acetal or (hemi)ketal.
eg. D-glucose (linear and pyranose forms)
H-C=O <- aldo carbon (C1)
|
H-C-OH
|
HO-C-H
|
H-C-OH
|
H-C-OH <- D(L) carbon
|
H-CH-OH
HO-HCH
|
D(L) carbon -> H C - O H
|/ \|
C OH H C <- hemiacetal carbon (C1) = anomeric carbon
|\| |/| alpha (down) in this configuration
HO C - C OH
| |
H OH
Hope the graphics comes out OK.
Annette.
Jerry Gaiser
> Hi- I recently bought a rice cooker (Singer brand) and the first time
> I used it, alot of the rice stuck to the bottom. I tried again using
> a little more water and spraying the pan with Pam but there was still
> rice stuck to the bottom. The pan itself is made of aluminum so I
> thought that might be the problem but I looked at a higher priced
> "Rival" brand model and it was made of the same thing. I live in
> Boulder (5400') which might have something to do with it but I'm
> not sure. Does anyone have any suggestions?
I think that's a standard thing with rice cookers. I have a Rival with an
aluminum pan and it always has rice stuck to the bottom. Since I cook almost
nothing but brown rice, I just use the rice paddle to scrape the bottom and
mix it all together. Adds a nice flavor to the rice.
--
Jerry Gaiser (jer...@jaiser.rain.com) (voice) 503-359-4017
Fidonet 1:105/380 (bbs) 503-359-5111
PBBS n7...@n7pwf.or.usa.na
.. I read banned books ..
Paul S. Winalski
In article <1992Dec28....@lclark.edu>, deg...@lclark.edu (David Degraw) writes:
|>
|>wina...@adserv.enet.dec.com (Paul S. Winalski) in,
|>Message-ID: <1992Dec27.2...@nntpd2.cxo.dec.com>
|>Article-I.D.: nntpd2.1992Dec27.212634.25439 writes,
|>
|>>>
|>>>alpha-linkage cleavage of disaccharides, but posessing the enzyme that
|>>>specifically cleaves alpha-D-glucose-(1->6)-D-fructose (aka D-sucrose).
|>
|>(rest of post deleted)
|>
|>In a reference book, sucrose is shown as a disaccharide comprised of
|>alpha-D-glucose ether bridged to D-sucrose. The bridge is a 1->2 ether
|>bridge involving the 1-carbon on the glucose and the 2-carbon on the
|>fructose.
Yes. My post was from memory, and when I dusted off my biochem textbook today
and read up on sugars, I saw that I made several mistakes. Sucrose is, as
you say, alpha-D-glucose in 1->2 glycocidic linkage to beta-D-fructose.
|>I imagine a bacterium lacking a general-purpose alpha-lysing enzyme
|>could not metabolize *any* sort of disaccharide (maybe beta-disachs?).
Such as cellobiose and cellulose. Such a bacterium would also be able to
survive if provided with monosaccharides as an energy source.
|>Is should be common knowledge that many bacterium can metabolize glucose
|>made along biosynthetic pathways. (i.e. bacterial have no trouble
|>metabolizing naturally-occuring alpha-D-glucose)
I was talking about alpha-glycocidic linkages in polysaccharides. The alpha-
and beta- forms of monosaccharide hemiacetals spontaneously interconvert in
aqueous solution (the equilibrium for D-glucose is about 60+% in beta
configuration), so alpha- vs. beta- stereoisomerism isn't a problem
biochemically.
|>
|>BTW Are there alpha and beta varieties of sucrose also?
No. Since the glucopyranose and fructofuranose moeties are joined at their
anomeric carbons, there is no free anomeric carbon to exist in alpha- or
beta- configuration.
--PSW
Paul S. Winalski
In article <dexter.725570507@aries>,
dex...@aries.scs.uiuc.edu (The Gecko) writes:
|>
|>wina...@adserv.enet.dec.com (Paul S. Winalski) writes:
|>
|>>Cells contain a wide variety of enzymes that can convert one isomeric form
|>>of a sugar to another (isomerases), split a sugar into two sugars, or merge two
|>>simple sugars into a longer sugar (transaldolase, transketolase). The end
|>>result of this is that all of the simple sugars, regardless of isomeric form,
|>>can be converted into D-glucose, the form that is burned in the main catabolic
|>>pathway for sugars to produce energy.
|>
|>>So the L-sugars *are* metabolizable, albeit more slowly than D-glucose, which
|>>is the isomer that most organisms prefer.
|>
|>>D- counterparts, and they do taste sweet. On the other hand, disaccharides
|>>with a beta linkage are not digestible, which is why humans cannot survive on
|>>a diet of leaves or wood. Cellobiose, the beta-1-6-D-glucose disaccharide,
|>>is not digestible, but I don't think it tastes sweet, either.
|>
|>example of a D-sugar being converted to an L-sugar, you have only mentioned
|>general examples of sugar metabolism which intercovert *D-sugars*. By using
|>the term "isomer" loosely, without defining whether you mean an anomer (alpha
|>or beta diastereomer, eg. alpha-D-glucopyranose vs. beta-D-glucopyranose), an
|>epimer (eg. D-glucose vs. D-mannose, or separately, D-glucose vs. L-glucose)
|>or an enantiomer, you confuse the argument. Transaldolase and transketolase
|>interconvert *D-sugars*. Without a further description of which "isomerase"
|>you mean, I can't discuss this issue further, but I would be very surprised
|>to hear of a mammalian (say) enzyme which converted L- to D-sugars.
You're right. My fundamental mistake was regarding how sugars are classified
L- or D-. I mistakenly thought that the distinguishing carbon for D-series
vs. L-series sugars was the one right next to the aldo- or keto- carbon, when
in fact it is the asymmetric carbon farthest away from that carbon. The
isomer interconversion that I was thinking of (via enediols) thus won't touch
the D- or L- configuration.
BTW, I thought "epimer" referred to stereoisomers that differ around the
configuration of one carbon only, in which case D-glucose and L-glucose,
which are mirror images and thus differ at all 4 asymmetric carbons, cannot
be epimers.
|> Then you have confused digestion and metabolism. Of course if we are
|>dealing with a free L-sugar then only absorption from the gut needs to occur
|>before metabolism can take place. But to say an L-sugar is "digestible" at
|>the same time that you affirm cellulose is not "digestible", implies that we
|>have enzymes to break down glycosidic linkages to L-sugars even though we
|>cannot deal with (many) beta linkages. To anyone with an idea of enzyme
|>specificity this is absurd. Why should we have enzymes with the specificity
|>to break down polymers which don't even occur in our diet?
You're right about my confusion of digestion and metabolism in this case.
However, digestive enzymes have a tendency to be relatively non-specific.
|> Finally, it is beyond me why you *expect* L-sugars to be sweet at
|>the same time that you expect that cellobiose is not.
Cellulose certainly isn't sweet, but I concede your point--cellulose isn't a
disaccharide, either, and polysaccharides such as starches do not taste sweet,
while many disaccharides do.
My biochemistry textbook says nothing about the stereospecificty of the
enzymes involved in sugar metabolism, probably because since in nature, nearly
all sugars are in D- configuration, the subject is relatively moot. Most of
the action in the enzymes of glycolysis seems to take place around carbon 1,
the exception being the initial phosphorylation of the terminal carbon. I would
expect that some of the enzymes in glycolysis might be able to act on L-
sugars, albeit at reduced rates, just as some of them can act on epimers and
other analogues of their normal substrates. Of course, the L-configuration
might end up holding the phosphate at the terminal carbon in such a position
that binding to the enzyme is impossible in most cases.
Have there been any kinetic studies of the glycolytic enzymes with respect to
D-/L- stereospecificty?
--PSW
Keith Robison
>Just a random thought. Wouldn't it be nasty if the stereoisomer of one
>of the common sugars turned out to be pharmacologically potent?
In Lewis Carroll's _Through the Looking Glass_ Alice worries that
looking glass milk might not be good for her. In Martin Gardner's
"Annotated Alice" he comments in a footnote that this is apparently
true, though I think he gives no reference.
Additionally, this is very true for most pharmacologically active
compounds -- the different stereoisomers have radically different
pharmacologies. A lot of companies are trying to produce single (or
limited) isomers of drugs because of this (the side-effects are often
due to a different isomer than the desired effects) by various means,
such as stereospecific chromatography, enzymatic synthesis, enzymatic
degredation of unwanted isomers, and non-enzymatic stereospecific
catalysts and reactions.
Keith Robison
Harvard University
Department of Cellular & Developmental Biology
Department of Genetics / HHMI
Mark Robert Thorson
story. When the great Emil Fischer (we always use the prefix "great" when
talking about this man; he practically invented organic chemistry) developed
the D- and L- system of classifying stereoisomers, he had to make a guess
as to which chemical structure of glyceraldehyde was the D form, and which
was the L form. He guessed right (as confirmed by X-ray diffraction studies
decades later), hence L-glyceraldehyde is levorotatory and D-glyceraldehyde
is dextrorotatory.
Another famous scientist was in a similar position about a century earlier.
Benjamin Franklin correctly concluded that the phenomenon of electricity
was the flow of a substance from a place where it was in surplus to a place
in which there was a deficiency. He had no way of determining what was the
direction of the flow, so he arbitrarily assigned + and - to what he guessed
were the areas of surplus and deficiency. He guessed wrong. As a consequence,
all equations dealing with electricity (Ohm's law, the power equation, etc.)
have the sign reversed with regard to the actual flow of electrons. All the
equations work out okay, as long as you apply them consistently. But if
you ever wondered, the flow of electrons is from - to +.
Phil Hughes
: Also, I was thinking of purchasing a rice cooker, but don't know
: whick brand(s) would be the easiest to cook non-white rice in, i.e.
: red rice, wild rice (yes, I know it's not REALLY rice), "sweet" rice,
: sticky rice, etc, etc. Also, I need to buy one that can cook other
: grains - wheat, barley, quinoa, etc, etc.
I bought a Tiger with no option buttons and regularly cook brown rice in
it with no problem. The secret is to add the right amount of water as all
the rice cooker does is sense that the cooking tub temperature has
increased above the boiling point of water and shut off the main heating
element. In the case of brown rice I add one less measure of rice than
is indicated by the water level (fill water to 4, add 3 measures of brown
rice, for example) and it works great.
I did buy the model with the teflon lined tub: I figure I am less likely
to die from eating teflon than aluminum.
--
Phil Hughes, SSC, Inc. P.O. Box 55549, Seattle, WA 98155 (206)FOR-UNIX
>>> Publishers of pocket references for UNIX, C, VI, Emacs, Ksh, MS-DOS, ... <<<
...!ssc!fyl or f...@ssc.com (206)527-3385
Jeff Frane
>c...@noaacrd.colorado.edu (Cathy Smith) writes:
>> Hi- I recently bought a rice cooker (Singer brand) and the first time
>> I used it, alot of the rice stuck to the bottom. I tried again using
>> a little more water and spraying the pan with Pam but there was still
>> rice stuck to the bottom. The pan itself is made of aluminum so I
>> thought that might be the problem but I looked at a higher priced
>> "Rival" brand model and it was made of the same thing. I live in
>> Boulder (5400') which might have something to do with it but I'm
>> not sure. Does anyone have any suggestions?
>I think that's a standard thing with rice cookers. I have a Rival with an
>aluminum pan and it always has rice stuck to the bottom. Since I cook almost
>nothing but brown rice, I just use the rice paddle to scrape the bottom and
>mix it all together. Adds a nice flavor to the rice.
I guess that's what you get for buying American. I have a National rice
cooker (made in Japan) with which I have literally cooked 100s of
batches of rice (white, primarily, although I have successfully cooked
brown rice in it). I have _never_ encountered this problem, and this
cooker, too, has an aluminum pot.
Pam! Good lord.
If it's not against your religion or anything, you might try rinsing the
rice first. I know, I know. Or perhaps it's the kind of rice you're
using. It's not <shudder> Uncle Ben's or anything, is it?
--Jeff Frane
--
gumm...@techbook.COM Public Access UNIX at (503) 220-0636 (1200/2400)
Marc Green
>jer...@jaiser.rain.com (Jerry Gaiser) writes:
>>c...@noaacrd.colorado.edu (Cathy Smith) writes:
>Pam! Good lord.
This kind of stupid, smartass response to a reasonable query is what makes
internet so unpleasant. Too bad there is no way to keep people like this
Frane bound and gagged until he grows up. If he grows up.
Anyway, as far as the question is concerned, my rice cooker, which is a
NATIONAL by the way, causes rice to stick to the bottom, but only if I
cook less than 1.5 cups. I'm not sure why, but rice cookers work better
for large quantities of rice.
The problem seems to be that the heating element doesn't cool fast enough
when the the switch pops up to warm, so there is some burning. I've
found a satisfactory solution is to unplug the rice cooker as soon as the
switch pops up and add a couple tablespoons of water to keep the rice from
burning while the element cools a bit. Even unplugged, the rice stays warm for
a good long time.
Marc Green
Trent University
Cathy Smith
country. The kind of rice I am using is Texamati which is an American
grown version of Basmati (e.g. long grain) which I rinsed according
to instructions. Some people have told me that sticking is normal and
expected though since you have said your rice doesn't stick i don't
know what to think.
It's not that I mind the sticking so much as that I don't get the full
amount of cooked rice- over a cup less than if I made it over the
stove. Also, even though I am following the instructions precisely,
some of the stuck grains are overcooked. I am still wondering how the
high altitude affects the cooking. Does anyone know how a rice cooker
determines that it is done the cooking phase. It can't go by
temperature since boiling temperature at my altitude is about 187F or
so.
My guess for the reason I get so much sticking is that since the heat
imparted during the cooking phase is constant and the temperature at
which the water vaporizes is less, more of the water evaporates.
I will try adding even more water to see if this is the case.
Bill Maniatty
|> gumm...@techbook.com (Jeff Frane) writes:
|>
|> >jer...@jaiser.rain.com (Jerry Gaiser) writes:
|>
|> >>c...@noaacrd.colorado.edu (Cathy Smith) writes:
|>
|> >>> Hi- I recently bought a rice cooker (Singer brand) and the first time
|> >>> I used it, alot of the rice stuck to the bottom. I tried again using
|> >>> a little more water and spraying the pan with Pam but there was still
|> >>> rice stuck to the bottom. The pan itself is made of aluminum so I
|> >>> thought that might be the problem but I looked at a higher priced
|> >>> "Rival" brand model and it was made of the same thing. I live in
|> >>> Boulder (5400') which might have something to do with it but I'm
|> >>> not sure. Does anyone have any suggestions?
|>
|> >>I think that's a standard thing with rice cookers. I have a Rival with an
|> >>aluminum pan and it always has rice stuck to the bottom. Since I cook almost
|> >>nothing but brown rice, I just use the rice paddle to scrape the bottom and
|> >>mix it all together. Adds a nice flavor to the rice.
|>
|> >I guess that's what you get for buying American. I have a National rice
|> >cooker (made in Japan) with which I have literally cooked 100s of
|> >batches of rice (white, primarily, although I have successfully cooked
|> >brown rice in it). I have _never_ encountered this problem, and this
|> >cooker, too, has an aluminum pot.
|>
|>
|> Anyway, as far as the question is concerned, my rice cooker, which is a
|> NATIONAL by the way, causes rice to stick to the bottom, but only if I
|> cook less than 1.5 cups. I'm not sure why, but rice cookers work better
|> for large quantities of rice.
|>
|> The problem seems to be that the heating element doesn't cool fast enough
|> when the the switch pops up to warm, so there is some burning. I've
|> found a satisfactory solution is to unplug the rice cooker as soon as the
|> switch pops up and add a couple tablespoons of water to keep the rice from
|> burning while the element cools a bit. Even unplugged, the rice stays warm for
|> a good long time.
|>
|> Marc Green
|> Trent University
|>
some tendency for the rice at the bottom to scorch a little and stick some to
the pan, I think our pan has a non-stick coating of some kind, and is always
easy to clean.
Bill
--
|
| mani...@cs.rpi.edu - in real life Bill Maniatty
|
Rmc Walker
the bottom, it must be in the genes :)
UUCP: humu!nctams1!pnet16!01f
ARPA: humu!nctams1!pnet16!0...@nosc.mil
INET: 0...@pnet16.cts.com
Jerry Gaiser
> gumm...@techbook.com (Jeff Frane) writes:
>
> >If it's not against your religion or anything, you might try rinsing the
> >rice first. I know, I know. Or perhaps it's the kind of rice you're
> >using. It's not <shudder> Uncle Ben's or anything, is it?
>
> >--Jeff Frane
> >--
> >gumm...@techbook.COM Public Access UNIX at (503) 220-0636 (1200/2400)
>
> This kind of stupid, smartass response to a reasonable query is what makes
> internet so unpleasant. Too bad there is no way to keep people like this
> Frane bound and gagged until he grows up. If he grows up.
>
Come on, give the guy a break. I personally think it depends on the rice
being cooked, the machine it's being cooked in and whatever else variable
you want to add. I didn't take it personal and no need for you to.
Linda Cline
>
>>>> Hi- I recently bought a rice cooker (Singer brand) and the first time
>>>> I used it, alot of the rice stuck to the bottom. I tried again using
>>>> a little more water and spraying the pan with Pam but there was still
>>>> rice stuck to the bottom. The pan itself is made of aluminum so I
>>>> thought that might be the problem but I looked at a higher priced
>>>> "Rival" brand model and it was made of the same thing. I live in
>>
>>>I think that's a standard thing with rice cookers. I have a Rival with an
>>>aluminum pan and it always has rice stuck to the bottom. Since I cook almost
>>
>>I guess that's what you get for buying American. I have a National rice
>>brown rice in it). I have _never_ encountered this problem, and this
>>cooker, too, has an aluminum pot.
>>
>>
>I believe (I will have to check) that it was made in a SE Asian
>country. The kind of rice I am using is Texamati which is an American
>grown version of Basmati (e.g. long grain) which I rinsed according
>to instructions. Some people have told me that sticking is normal and
>expected though since you have said your rice doesn't stick i don't
>know what to think.
>
>Cathy Smith
>c...@noaacrd.colorado.edu
>
I have a Sanyo rice cooker and have never had browned or sticking rice.
My mom (who is Japanese) bought this for me, and also has always had
Japanese made rice cookers while I was growing up and never encountered
this problem. If I want browned rice for some reason (usually when
serving a fancy dish with white rice, I want it all white for aesthetic
reasons), I can brown it in a saute pan. I do have a friend who tried an
Oster brand rice cooker and had browning/sticking problems. He determined
the problem (since trying mine previously, he felt the browning/sticking
was a problem) to be related to the cooking temperature and fit his cooker
with some kind of wire spacer between the cooking element and the pot
(similar to those used with electric ranges to keep pans at a cooler
temperature than is possible with the temperature control). I don't know
much about the details of his solution, but he was pleased with the result.
Don't know if this info helps...
linda
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
"Now, here, you see, it takes all the running you can do, to keep in
the same place. If you want to get somewhere else, you must run at
least twice as fast as that!"
Lewis Carroll
Through the Looking Glass
Linda Cline
Intel Supercomputer Systems Division
Compiler Group
email: l...@ssd.intel.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Jung Tjong
I have a 3 serving size panasonic rice cooker.
What I found is: if I open the cover and take the rice immediately after the cooking stops
the rice at the bottom sticks to the pan. I think because the pan is still hot and
as the cover is opened, the vapor is released and the rice dries up on contact with the pan.
If I wait a while until the pan cools down a bit, I don't have that problem.
Try it. 'hope it works with yours.
Jung
BOUCHER DAVID
>Various drug protocols in Europe specify infusion of glucose, while similar
>protocols in the United States usually specify dextrose.
"Dextrose" and "glucose" are different names for the same substance. The nomenclature stems from the fact that glucose is the most common dextrorotary
monosaccharide.
Incidentally, fructose is also known as "levulose" for a similar reason.
- db
Mark Robert Thorson
> >protocols in the United States usually specify dextrose.
>
> "Dextrose" and "glucose" are different names for the same substance. The nomen
> clature stems from the fact that glucose is the most common dextrorotary
> monosaccharide.
>
> Incidentally, fructose is also known as "levulose" for a similar reason.
I thought that "dextrose" and "levulose" are terms for industrial commodities,
which are mixtures of invert sugars which are respectively dextrorotatory
and levorotatory, while glucose and fructose refer to specific molecular
structures. (Granted that glucose is the dominant dextrorotatory component
of invert sugars, and that fructose is the dominant levorotatory species.)
Dave Huddle
writes:
|> I thought that "dextrose" and "levulose" are terms for industrial
|> commodities,
|> which are mixtures of invert sugars which are respectively dextrorotatory
|> and levorotatory, while glucose and fructose refer to specific molecular
|> structures. (Granted that glucose is the dominant dextrorotatory component
|> of invert sugars, and that fructose is the dominant levorotatory species.)
NO!
From Chem. Abstracts-Index Guide
Dextrose--see D-glucose [50-99-7] Levulose--see D-Fructose [57-48-7]
CHO CH2OH
| |
H-C-OH C=O
| |
HO-C-H HO-C-H
| |
H-C-OH H-C-OH
| |
H-C-OH H-C-OH
| |
CH2OH CH2OH
BOUCHER DAVID
> [...] mixtures of invert sugars [...]
"Invert sugar" is a 50-50 mixture of glucose and fructose such as may be
produced by the hydrolysis of sucrose. It is called "invert" sugar because
natural sucrose is dextrotary, but in a 50-50 mixture of glucose and fructose,
the levorotary influence of fructose wins out.
-db
Mickey Rowe
whose readers probably ought to hit 'n' now.
In article <72...@cup.portal.com> m...@cup.portal.com
(Mark Robert Thorson) writes:
}Another famous scientist was in a similar position about a century earlier.
}Benjamin Franklin correctly concluded that the phenomenon of electricity
}was the flow of a substance from a place where it was in surplus to a place
}in which there was a deficiency. He had no way of determining what was the
}direction of the flow, so he arbitrarily assigned + and - to what he guessed
}were the areas of surplus and deficiency. He guessed wrong. As a consequence,
}all equations dealing with electricity (Ohm's law, the power equation, etc.)
}have the sign reversed with regard to the actual flow of electrons. All the
}equations work out okay, as long as you apply them consistently. But if
}you ever wondered, the flow of electrons is from - to +.
Since this was cross-posted to sci.bio, I have to insist that you cut
Benny some slack on this one... Although electrons are the charge
carriers of interest in many physical systems (including those that
Ben was studying), in most of the systems that are nearest and dearest
to our hearts (like for instance the cell membranes in cardiac muscle)
the charge carriers are positive ions--principally Na+, K+ and Ca++.
If Benny had gone the other way, there'd still be people bitching
about it the charge carriers moving in the opposite direction of
"current flow" in many systems of interest :-)
Mickey Rowe (ro...@pender.ee.upenn.edu)
Andrew Corradini/SBDC
>>If such a product existed, it wouldn't taste sweet, would it?
>
>As I understand it, mannitol and sorbitol are such. I've never quite figured
>out why they aren't used more.
>
Wrongo on both counts... L-sugars would definitely *taste* sweet -- this
has been shown in laboratory preparations of such. They possess the
bio-chemical properties that mesh nicely with the "sweetness-receptors" in
the papillae (taste-buds). However, all the naturally-occurring sugars
are dextro (R-sugars), and all the enzymes found in nature will break down
*only* these sugars, thus releasing energy. More to the point, L-sugars
could not possibly combine chemically with the entire Earth spectrum of
compounds to produce, say, fatty acids and thus "fat" in the human body.
The major problem is that virtually the only way to produce any kind of
"sugar" (C6 H12 O6 and compounds thereof) is to derive them from naturally
occurring sources -- all of which, due to a quirk of fate, are dextro-.
Lab synthesis of L-sugars is possible, but currently is on the order of
hundreds to thousands of dollars per gram. If somehow you could produce
the exact mirror image of one single cell, with its tens of millions of
atoms and indescribably complex molecular structures (particularly the
DNA spiraling the "wrong" way), you'd be a bazillionaire.
Andrew Corradini/SBDC
>
>In article <72...@cup.portal.com>, m...@cup.portal.com (Mark Robert Thorson)
>writes:
>
>>>Please excuse the cross-posting into the sci newsgroups, but we've been
>>>having a discussion in rec.food.cooking about the supposed existence
>>>of left-handed sugars which are indigestible hence calorie-free.
>>>I contend that if L-sugars were calorie-free, they probably wouldn't
>>>be sweet, either. Can someone in the sci groups clarify this?
>
>Common table sugar is sucrose, an enatiomeric molecule. The stuff
>can metabolize only R-sucrose. A technique I read about to isolate
>alpha-L-glucose used a microorganism (I don't have the refernce for which
>kind) which selectively metabolized alpha-R-glucose.
>
>taste receptors.
>
>Both R and L sucrose should be digestible since only a fraction of human
>digestion is carried out by bacteria. Most of the digestion of
>sucrose occurs in the small intestine where it is lysed by sucrase into
>glucose and fructose. Glucose and fructose are then transported to the
>liver for storage via the intestinal capillaries. Although most of the
>bacteria live in the small intestine, they seem to play a small role in
>sucrose digestion
This sounds real scientific and all, although you use several spellings of
enantiomer/enatiomer and I think the use of "levorotatory" was probably
just a typo ;-) of levorotary... Terminology notwithstanding...
Glucose and fructose each occur in both dextro- and levo-rotary isomers.
The resulting sucrose is merely a compound of the two. By "occur", I
should say, *could* occur, since in nature, all simple sugars (e.g.,
glucose, fructose, galactose, etc.) are found exclusively in the dextro-
form. The formation of DNA, and thus the cellular mechanisms responsible
for sugar formation, are exclusively dextro-rotary. Elsewise, we would
have organisms capable of digesting only those of equivalent "polarity",
or (pardon the liberty), "sugar-sex".
If the two types of sugars occurred in nature equally (pardon me:
"racemically"), only half the sugar in any box/ice-cream-cone/cake would
be digestible, since the greatest part of sugar metabolism is carried out
intra-cellularly, and human enzymes (as with all Earth critters) are
exclusively dextro-rotary. The referenced posting was full of really nice
information and neat-o bioterminology; the conclusion, however, was
completely wrong-o.
I regret having no citations at hand, but I did extensive research as an
undergrad on this topic, since it seemed like a good
get-rich-reasonably-quick scheme if you could find a differentiatory
"sieve" for L-sugars. Many commercial labs have *produced* (*NOT*
extracted!) L-sugars, but the cost is as of yet prohibitive.)
Sorry, David,
Andrew
Keith Robison
>The formation of DNA, and thus the cellular mechanisms responsible
>for sugar formation, are exclusively dextro-rotary. Elsewise, we would
>have organisms capable of digesting only those of equivalent "polarity",
>or (pardon the liberty), "sugar-sex".
>
Just because DNA is dextrorotary does NOT rule out the possibility of
"reverse-handed" biomolecules. "Wrong"-handed amino acids are a
critical component of bacterial cell walls, and also of many antibiotics.
Andrew Lewis Tepper
by SB...@u.cc.utah.edu
>undergrad on this topic, since it seemed like a good
>get-rich-reasonably-quick scheme if you could find a differentiatory
>"sieve" for L-sugars. Many commercial labs have *produced* (*NOT*
>extracted!) L-sugars, but the cost is as of yet prohibitive.)
matches the news blurbs I heard years ago. I did some research and found
that left handed sugars occur in nature in 3 places: Blue-Green algae,
Flaxseed, and Mountain Ash berries. There is a company in Chicago (was?)
working on producing L.H. sugars cheaply. When I called them (5+ years
ago) they were not at all willing to talk about their work, but did say
that coke and pepsi had both invested in their company. When I asked how
much L.H. sugar cost to produce at the time, they smugly replied
"Somewhere between the cost of table sugar and $30,000 per gram." Also,
they were trying to synthesize L.H. fructose, and several other kinds of
sugars with bizarre spellings that I've never heard of. They said that
sucrose was basically impossible because it's to complex. I don't
remember the company name. (That was one of the things I was looking for
with my original post.)
What about growing mountain ash trees and refining sugar from their
berries? (For all I know they contain 1% LH Sugar and 99% RH sugar...)
My parents have a half dozen of these trees in their yard.
If anyone has info about the Chicago lab/company, please post or e-mail!
Andy
The Gecko
>This sounds real scientific and all, although you use several spellings of
>enantiomer/enatiomer and I think the use of "levorotatory" was probably
>just a typo ;-) of levorotary... Terminology notwithstanding...
I think "levorotatory" is correct. I have not heard of "levorotary",
myself. Same for "dextrorotatory".
>Glucose and fructose each occur in both dextro- and levo-rotary isomers.
>The resulting sucrose is merely a compound of the two. By "occur", I
>should say, *could* occur, since in nature, all simple sugars (e.g.,
>glucose, fructose, galactose, etc.) are found exclusively in the dextro-
>form. The formation of DNA, and thus the cellular mechanisms responsible
>for sugar formation, are exclusively dextro-rotary.
Wrong terminology. They are D-sugars, which is not the same as being
dextrorotatory.
>intra-cellularly, and human enzymes (as with all Earth critters) are
>exclusively dextro-rotary.
It makes no sense to call an *enzyme* dextrorotatory. You mean they
act on D-sugars. Fine. Not the same as acting on dextrorotatory sugars.
Annette.
Erick Singley
There was a write-up 2-3 years ago about his company in the Washington Post.
He claimed that his process could use what the dairy industry threw out, and
process these 'off-handed' sugars for prices comparable to that of cane sugars.
(Once large scale, I would guess). The one big thing keeping him back was the
govenment approval and testing. Apparently (?) there must be some $ outlay by
his company to start private testing before government testing. (ie safety
and whatnot) So, his company makes other stuff in order to finnaly fund this
larger future project.
Erick
--
sin...@clinpharm.niaaa.nih.gov
Dawn Burgess
>asc...@u.cc.utah.edu (Andrew Corradini/SBDC) writes:
>
>
> I think "levorotatory" is correct. I have not heard of "levorotary",
>myself. Same for "dextrorotatory".
>
>
> Wrong terminology. They are D-sugars, which is not the same as being
>dextrorotatory.
You are right, but a little more explanation seems in order. D-sugars are
named as such because of the arrangement of the atoms in the molecule. The
term dextrorotatory means that if you make a solution of a dextrorotatory
sugar and pass plane-polarized light through the solution, the plane of
polarization is rotated clockwise (opposite for levo). D-molecules are
not necessarily dextrorotatory.
Dawn
Thomas Rich Schwerdt
>In article <1992Dec27.1...@lclark.edu> deg...@lclark.edu (David Degraw) writes:
>>
>>In article <72...@cup.portal.com>, m...@cup.portal.com (Mark Robert Thorson)
>>writes:
>>
>>
>>digestion is carried out by bacteria. Most of the digestion of
>intra-cellularly, and human enzymes (as with all Earth critters) are
>exclusively dextro-rotary. The referenced posting was full of really nice
Just an idea, if Andrew's right - if the levorotary (L-sugars) are not
digestible, wouldn't the effect of eating L-sugar be the equivalent
of lactose intolerance, with a few unhappy side-effects?
Sorry tothrow a damper, but i'm trying to answer the original food question
to the best of my lowly knowledge....
pardon the typos, but this is a very poor editor to revise on.
-Tom
Keith Robison
>Just an idea, if Andrew's right - if the levorotary (L-sugars) are not
>digestible, wouldn't the effect of eating L-sugar be the equivalent
>of lactose intolerance, with a few unhappy side-effects?
It all depends on what the bacteria in your digestive tract
can digest. "Lactose intolerance~ is not some bodily reaction
to undigested lactose, it is the unpleasant side-effects of your
gastrointestinal flora eating what you don't (I believe the notorious
effects of beans are in the same league).
Paul S. Winalski
In article <C0vKn...@news.udel.edu>,
py...@bach.udel.edu (Thomas Rich Schwerdt) writes:
|>
|>Just an idea, if Andrew's right - if the levorotary (L-sugars) are not
|>digestible, wouldn't the effect of eating L-sugar be the equivalent
|>of lactose intolerance, with a few unhappy side-effects?
Terminology nit: "levorotary" means that the chemical compound rotates polarized
light in a left (counterclockwise) direction. The "L-" prefix on chemical
compounds refers to a specific isomeric configuration of the compound, relative
to some reference compound (in the case of sugars, glyceraldehyde). The two
characteristics (dextrotation versus levorotation and D-series vs. L-series
stereoisomeric configuration) have nothing to do with each other. For
example D-fructose is levorotary.
Biochemically, it is the D- versus L- configuration that is important. Nearly
all naturally occurring sugars are in the D-configuration. Based on the
discussion here, it looks like L-sugars are not metabolizable by most organisms,
including humans.
The bad effects of lactose intolerance aren't due to the body's inability to
digest lactose. Rather, they happen because bacteria in the gut *do* digest
the lactose (which they normally don't get because it's digested by the gut
and absorbed). It is the waste products of these bacteria that cause the
problems. Since most bacteria can't handle L-sugars, either, I wouldn't expect
this sort of effect.
--PSW