From owner-biophysics@net.bio.net Tue Jan 13 22:00:00 1998 Path: biosci!agate!ihnp4.ucsd.edu!munnari.OZ.AU!news.mel.connect.com.au!news.syd.connect.com.au!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!peernews.ftech.net!news.ibm.net.il!ibm.net!news.biu.ac.il!news.huji.ac.il!not-for-mail From: "Jonathan B. Marder" Newsgroups: bionet.biophysics Subject: Re: Chemiosmotic mechanism Date: Wed, 14 Jan 1998 09:48:17 +0200 Organization: Hebrew University Lines: 77 Message-ID: <69hqk4$nq8$1@news.huji.ac.il> References: <69b5o0$pdv@mserv1.dl.ac.uk> NNTP-Posting-Host: marder.agri.huji.ac.il Mime-Version: 1.0 Content-Type: text/plain; charset="utf-7" Content-Transfer-Encoding: quoted-printable X-Newsreader: Microsoft Outlook Express 4.72.2106.4 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.2106.4 Pentcho Valev wrote in message = +ADw-69b5o0+ACQ-pdv+AEA-mserv1.dl.ac.uk+AD4-... +AD4-Jonathan Marder wrote:+AD4APgA+AD4APgA+AD4APgA+AD4APgA+- +AD4- You need look no further than chemiosmotic coupling. The normal +AD4-consensus is coupling of 3 protons per ATP. Typical proton motive = forces +AD4-are up to 180 meV which translates to roughly 52kJ per 3 protons +AD4-This would represent perfect coupling. +AD4-Even with a 2 protons per ATP coupling ratio, deltaH is still +AD4-insufficient to account for the work done. Does this meet your = criterion +AD4-of APPROACHing = reversibility?+ADwAPAA8ADwAPAA8ADwAPAA8ADwAPAA8ADwAPAA8ADw- +AD4- +AD4-Jonathan, I am not very competent in this but my interest is great. = Let us +AD4-first clarify a few things. +AD4- +AD4-1. How do we know the number of protons per molecule ATP? I have = read a few +AD4-times that it is derived thermodynamically, but is there an = independent +AD4-experimental confirmation? +AD4- There have been measurements made correlating pH changes with ATP = synthesis (tho' I can't cite a reference offhand). Because of various = discrepencies between labs. and methods, we can't be sure of the = definitive stoichiometry. However, AFAIK the consensus is 3 protons per = ATP. +AD4-2. How do we know the real proton motive force? For instance, the +AD4-transmembrane potential difference is inversely proportional to the +AD4-capacitance of the membrane. The ATPase complex is thick and +AD4-hydrophilic, i.e. the capacitance of that spot can be enormous and, +AD4-accordingly, the transmembrane potential difference almost zero. This is irrelevant. A p.d. is a p.d. irrespective of what lies between = the two points. The Mitchell view is to look at the protons in the bulk phase (tho' a = few dissenters claim that +ACI-special pools+ACI- of protons are = involved). Bulk phase proton-motive force is quite easy to measure using = various microelectrodes, pH-sensitive dyes etc. +AD4- +AD4-3. If delta H (20 KJ/mole) is insufficient to account for the work +AD4-done (e.g. 52 KJ/mole), where does the rest of the energy come = from? +AD4-It could only be heat absorbed, but Bryant would object (I do not = know +AD4-why). As I stated before, the substrate/product concentration ratios are part = of the entropy term. I see no problem with entropy changes doing work. = It is you Pentcho, not Byrant, who has a problem with this. +AD4- +AD4-4. I am surprised to hear that this maximal value (52 KJ or 3 = protons) +AD4-corresponds to +ACI-perfect coupling+ACI-. ... +AD4AWw-the reaction+AF0- is close to equilibrium? (At least papers say = so).=20 By +ACI-perfect coupling+ACI- I meant that the deltaG for ATP/ADP and = the deltaG for proton movement add up to zero (equilbrium indeed) so = there is no wasted energy. Of course, this is only under certain = conditions. +AD4-Then why did you +AD4-and Bryant reject the same interpretation in other cases? Did we? I hope not+ACE- Perhaps there is a misunderstanding. Regards, Jonathan .