[RASMB] time to reach equilibrium

Allen P. Minton minton at helix.nih.gov
Mon Jun 9 06:17:00 PDT 2003


Let me put in my two cents' worth on the issue of equilibration time for
proteins undergoing indefinite polymerization (a la actin, tubulin).  It
was recognized some time ago (I think originally by Oosawa and Asakura,
and Damien Hall and I have recently studied this in some detail) that
reversible (as opposed to irreversible) polymerization takes place in two
fairly distinct time domains.  The fast phase is the incorporation of
monomer into polymer.  The slow phase is the redistribution of protomers
between polymers to achieve the final equilibrium distribution of polymer
lengths.  The redistribution phase is essentially entirely entropy-driven
and may require orders-of-magnitude longer time than it takes to achieve
the initial polymerization.  Note that the slow phase, while not
significantly changing the amount of polymer, will change the mass
distribution, and hence the weight-average-molar mass, and hence the
concentration gradient in the centrifuge.  Caveat experimentor!





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