From owner-biophysics@net.bio.net Sat Jan 10 22:00:00 1998
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From: "Jonathan B. Marder" <marder@agri.huji.ac.il>
Newsgroups: bionet.biophysics
Subject: Re: Towards an agreement about chemical work
Date: Sun, 11 Jan 1998 17:59:11 +0200
Organization: Hebrew University
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Pentcho Valev wrote in message =
+ADw-69307i+ACQ-47i+AEA-mserv1.dl.ac.uk+AD4-...
...
+AD4-It is said in textbooks that, if delta G for the ATP system is -50 =
KJ/mole,
+AD4-one can expect maximum 50 KJ/mole work to be done by the ATP =
system.
+AD4-As delta H for ATP hydrolysis is 20 KJ/mole, it follows from /1/ =
that
+AD4-Q, the heat absorbed as maximum work is done, is 30 KJ/mole.
+AD4-
+AD4-Everybody would agree that the ATP system NEVER does the maximum =
work, i.e.
+AD4-work production in this case cannot be REVERSIBLE. What is not =
clear however is
+AD4-whether the value of 50 KJ/mole can be APPROACHED. ...

Pentcho,
  You need look no further than chemiosmotic coupling. The normal =
consensus is coupling of 3 protons per ATP. Typical proton motive forces =
are up to 180 meV which translates to roughly 52kJ per 3 protons+ACE- =
This would represent perfect coupling.
Even with a 2 protons per ATP coupling ratio, deltaH is still =
insufficient to account for the work done. Does this meet your criterion =
of +ACI-APPROACHing+ACI- reversibility?

Jonathan B. Marder   +ADw-MARDER+AEA-agri.huji.ac.il+AD4-
Department of Agricultural Botany, The Hebrew University of Jerusalem
Faculty of Agriculture, P.O.Box 12, Rehovot 76100, ISRAEL
Phone: +-972 8 9481918   Fax:   +-972 8 9467763  =20
Web page:    http://www.agri.huji.ac.il/+AH4-marder



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