Thermogenesis via leaky mito membranes, is the proton channel getting hot or does the proton react?

[Nathan McCorkle]

So I can't find concise info on the exact source of heat radiating from mitochondrial leaky membrane thermogenerating systems. In brown adipose tissue the proton channel UCP-1 allows protons to bypass ATP synthase, but once the protons get to the other side, do they just form water with random OH- or NAD+ or some other redox carrier?

Is the heat generated in UCP-1, like a bunch of small interactions that amount to a something like friction, or from an exothermic reaction?

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-Nathan

[Matthias Bock]

Up to my knowledge, there are two different things: delta pH and delta Psi, corresponding to:

delta pH: difference between proton concentrations, but no charge, all protons have counterions.

delta Psi: electrical potential at the inner membrane, involving charge, like in a capacitor.

(Both seems to play a role in mitochondria: Having no charge,

but pH differences, can still drive the ATP synthetase)

In general, the protons do not need any other compound in their role as potential energy keeping agents,

not OH- or NAD+ or any redox carrier.

It is just protons being pumped outside the matrix, and just protons,

which's inflow to the matrix drives ATP synthetase.

There is an electrical potential driven ADP/ATP exchanger though, so

the ratio between ADP which is 3- and ATP which is 4-, may also play a role...

In conclusion, in both cases proton gradients represent order (instead of entropy),

meaning that the very mixing of matrix and intermembrane space leads to "liberation" of free enthalpy,

rising the temperature.

Hope I used the right words, hope it helps :-)

Best, Matthias

[Cathal Garvey (Android)]

I don't know the answer, but I think I recall reading about decouplers being used in mammals to free energy from the usual electron transport chain? Literally just blocking the usual efficient energy capture to let a high energy electron loose, where it dumps energy in the usual ways.

Could be nonsense but might provide duckduckgo fodder. :)

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[Matthias Bock]

Interesting. The last time I heard of electrons,
decoupled or leaking from the electron transport chain,
it was in the context of production of reactive oxygen species.

Do you happen to know, what happens to this "leaking" electrons,
when they are not used to reduce oxygen to water ?

Best, Matthias

[Cathal Garvey]

A bit of duckduckgo-ing yields:
https://en.wikipedia.org/wiki/Thermogenin
https://en.wikipedia.org/wiki/Uncoupling_protein

..but also corrects my supposition that this is behind normal
thermogenesis in mammals. There is in fact no mention of how heat is
generated in the Liver, whether by this or some other means. According
to the articles on non-shivering thermogenesis, it's used by infants
and hibernating mammals; this suggests something else is afoot in
normal thermogenesis for adult actives.

And yea, the decouplers seem to just allow protons to move through
without involvement of electron transport chains, so it's not free
electrons, just the dumping of potential energy from the proton
gradient. How this yields heat in "common sense" terms is probably hard
to explain, I don't understand it myself; as you say, it's all down to
an increase in entropy. :)

[Matthias Bock]

> I don't understand it myself; as you say, it's all down to 
an increase in entropy. :) 

Yes, I think I don't fully understand it either.

I think of it as protons, which are accelerated in the Thermogenin channel

due to the present gradient, because they are so to say attracted by the other side of the membrane,

and that this velocity dissipates through hits on other molecules,

such that the average molecule velocities locally increase, corresponding to increase in temperature.

Or maybe it's totally different :-)

LG

[Nathan McCorkle]

Your explanation made me think of sodium acetate heater pads, they go from being supersaturated to rapidly crystallising and giving off heat. I believe the supersaturated state has more energy because all the molecules would be more relaxed in a crystal, I'm not sure about entropy in this case though as both the supersaturated high-energy state has order, and the crystal state has order too. Since entropy is a measure of disorder right, I guess the crystal is actually more disordered than the solution???

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-Nathan

[John Griessen]

On 12/14/2012 02:51 PM, Nathan McCorkle wrote:
> Your explanation made me think of sodium acetate heater pads, they go from being supersaturated to rapidly crystallising and
> giving off heat. I believe the supersaturated state has more energy because all the molecules would be more relaxed in a crystal,
> I'm not sure about entropy in this case though as both the supersaturated high-energy state has order, and the crystal state has
> order too. Since entropy is a measure of disorder right, I guess the crystal is actually more disordered than the solution???
>

Nahh. You may have a definition problem in your last statement. The entropy needs to be defined
in terms of the whole, crystals, water, plus surroundings accepting heat.

It's fun how sodium acetate can stay liquid until a vibration sets it off crystallizing.
I'd not heard of that before.

Heat flows out of most solutions as they precipitate out crystals. AKA heat of solution or reaction.

Formation of bonds releases energy is another way to think of it. Precipitating crystals is obvious
ionic bonds of crystal lattice forming.

Solution reactions that make bonds without precipitation would be exothermic also.