Living organisms and thermodynamics (Pentcho Valev)

Sat Oct 11 07:42:19 EST 1997

(Sorry for writing my name in the subject space - the reason is that my
messages are archived under somebody else's name)

In reply to Anita Armstrong

The validity of the second law of thermodynamics has never been proved or
disproved, so, in my opinion, one should never stop looking for possible
violations. Let me present an oversimplified picture of what I believe
could have been the first bioenergetic cycle. Please consider the following

                               low pH

membrane-permeable-to-H+ only // impermeable-membrane-------------X-------

                               high pH

At equilibrium, a capacitor-like double layer is established where the
membrane is permeable to H+ and, accordingly, a transmembrane electrical
potential opposes the H+ concentration gradient. This is a common and
universally accepted picture. The essential problem is: Does this
electrical potential reach the point X situated on the impermeable
membrane, far enough from the permeable one? In other words, is there, at
the point X, a transmembrane electrical force which would oppose eventual
movement of H+ down the concentration gradient? If not (as I believe),
an ATPsynthase placed at the point X could use this movement of H+ down
the concentration gradient for ATP synthesis. As the "working" system
is at equilibrium, this would be a violation of the second law.
   The only contradictory point is whether or not the electrical potential
extends far from the semipermeable membrane. This can be verified for
another, even more simplified, system:

     10 mM  KCl                  M                        1 mM KCl

where M is a membrane permeable only to K+.
   For this system thermodynamics says that, at equilibrium, the
electrical potential difference between points symmetrical with respect
to but far from the membrane remains constant - 60 mV. However there is
serious reason to believe that the potential approaches zero with
distance, in both directions. There has been a discussion in the biophysics
group on this problem but to no avail. Yet this is very easy to verify
experimentally, and a colleague (Herman Berendsen from Groningen) agreed
to do the experiment (I am unfortunate to live under conditions allowing
no experimental activity). If the potential does indeed approach zero
with distance, the implications both thermodynamic and bioenergetic would
be even difficult to imagine.

Best regards,
Pentcho Valev

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