David Fell wrote:
>> [...] 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.
Well, with a bit of tongue in cheek, one could say that this
non-obvious nature and role of metal-trafficking proteins is the main
reason why certain people are studying them [see also Science, 292,
2488 (2001)].
On a more serious note, I always thought that one does not have to
have net flux of *particular* molecules or ions (such as Zn++) to
observe a cell at disequilibrium with respect to those same chemical
species. Couldn't it be that protein *turnover* inside the cell, in
this case the synthesis of 'ZntR' and 'Zur' zinc trafficking proteins
and their degradation by proteases, is keeping the cell at
disequilibrium with respect to Zn++? It might be be interesting to
see what is the half-life of these metal binding proteins.
> 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 [...].
Absolutely. This would be another expression of "kinetic control",
wouldn't it?
- Petr
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