Petr Kuzmic wrote:
>Consequently, thermodynamic equilibrium constants measured for
>individual enzymes are not applicable to the cell, at least in certain
>documented cases such as Zn trafficking. In other words, zinc or copper
>concentrations in the cell are never at thermodynamic equibrium,
The general point, that the cell has to maintain a non-equilibrium state
for the kinetic factors to be dominant, was one that I was going to make,
but you beat me to it. However, what puzzles me in this case is that the
way living systems keep away from equilibrium is by being open systems with
a flow of matter. I doubt there's a major flux of Zn or Cu through the
system, so what is the disequilibrium of these ions supposed to be coupled
to? It's not obvious to me that appeals to metal chaperones fit the bill here.
Also, a small number of free atoms/ions is not by itself an argument for a
difficulty in attaining equilibrium, since it's the rate at which these are
exchanging with the bound sites that also counts (c.f. protons - similarly
rare in a bacterial cell).
David
===================================================
Prof David A Fell,
School of Biological & Molecular Sciences, Oxford Brookes University,
Headington, Oxford OX3 0BP, UK
Tel: +44 (0)1865 483247 Fax: +44 (0)1865 484017
http://mudshark.brookes.ac.uk/
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