Can ATP do work at equilibrium? (Pentcho Valev)

RUMYM at BGEARN.ACAD.BG RUMYM at BGEARN.ACAD.BG
Sat Nov 1 05:16:32 EST 1997


Concerning the reaction far from equilibrium

   ATP + B = ADP + P + C                                    /1/

Bryant Fujimoto wrote:
So what is wrong with Delta G? That is, what is there you would want to<
know about the system that can't be described by thermodynamics or     <
statistical mechanics (at least in principle).                         <

There is nothing wrong with delta G so far as it shows the direction of
the reaction. But I would like to know how much work the system ATP-ADP-P
does on the system B-C. Would you tell me how to find it (at least in
principle)? This is not just a curiosity - after all, the second law is a
statement about the work a system does, so in order to verify the law we
need to know how much this work is.
   I would also like to know how much work the system ATP-ADP-P  does on
the system B-C when the reaction /1/ is at equilibrium. You would probably
answer that this work is given by delta G of the reaction  ATP = ADP + P,
but I would paraphrase this answer like this: "The work done is as much as
the second law says it is". Moreover, you probably remember that, long time
ago, Guy Brown declared in the biothermokinetics group that delta G is not
an energy - some were rather surprised, but then everybody thrust their
heads in the sand and life became calm again.
   So the experiment I proposed aimed at verifying whether or not reversible
work done by ATP is really equal to (the negative of) delta G. Theoretically
this is simple - as an ATPase transports, almost reversibly, H+ against an
electrical gradient, I expect the work done by one mole ATP to be not
greater than the internal energy (enthalpy) of one mole ATP, i.e. 20 KJ/mole.
Thermodynamics predicts that the work done can be much greater - e.g.
50 KJ/mole. This means that, as one mole ATP does work, it uses not only
its internal energy but also absorbs 30 KJ/mole heat from the environment
and converts it into work too. It is just this heat absorption that bothers
me - on one hand, its value must depend on the concentrations of the
reagents, i.e. it is a statistical phenomenon; on the other, the work
production consists of one mole independent chemical acts so no  such
statistics is physically plausible.
   I do not think that the second law has been confirmed many times in
many different experiments. This is simply impossible - in most cases
the chemical work is not at all defined. The only confirmation I know of
are galvanic reactions( a very interesting topic which also was found
uninteresting in the btk group). If you know of other experiments, please
describe them. If they are more interesting than those which I propose,
we will discuss them.
   There is another "uninteresting" way allowing one to verify the second
law - by analysing the countless implications. For instance, a derivation
based on the second law leads to to an obviously correct result - the
osmotic equation. If, as I believe, the second law is not valid, how is
this possible? I would be happy to discuss such problems, bur have a very
sad experience in the btk group. (You probably remember also that I found
a mistake invalidating Prigogine's theorem of minimum entropy production
at steady state, someone confirmed my conclusion, but then again heads were
in the sand and my distorted psychology became the most interesting
problem.)

Best regards,
Pentcho



More information about the Bioforum mailing list