Conversion between different Vmax units

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Hikmet Emre Kaya

Oct 6, 2022, 9:12:09 AM10/6/22
to COPASI User Forum

This might be a very ridiculous general question but here we go:

I am trying to add a reaction for the metabolism of a drug by the enzyme CYP3A4. The problem is, all literature Vmax values are either in pmol/min/mg or pmol/min/pmol CYP3A4, while COPASI asks for Vmax units in the form: mol/h or mol/(h*L)

I am not an expert on enzyme kinetics, so I am not sure how one makes the conversion to fit the Vmax data into a COPASI model. Do we need the enzyme concentration (in g/L or in M), as well as the incubation volume?

Some insight would be highly appreciated.

Hikmet Emre Kaya

Oct 13, 2022, 10:01:34 AM10/13/22
to COPASI User Forum
Following up on this:

I am actually struggling to reproduce the kinetic parameters of a study for my own research. They created an in silico model with a series of reactions and metabolites. For example, the Vmax value for the enzyme CYP3A4 is computed as 700 µM/h. However, when I look at the paper they are referencing, I can't obtain the same value.
In the referenced paper, the Vmax is given as ~2.7 nmol/min/nmol enzyme (supp-4). The supplementary material (supp 1) indicates that the enzyme concentration was 40 pmol/mL, and the final volume was 200 µL. With these values, I am not getting the same Vmax that they used in the computer model.
I am simply multiplying the Vmax value by the number of moles of enzyme, and then by 60 (to convert to per hour). So, I feel like I might be missing a step along the way :(
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