From: Dr A.J. Rowe <ajr@leicester.ac.uk>
  To  : Jim Cole <jim_cole@merck.com>
  Date: Mon, 6 Nov 1995 10:21:39 +0000 (GMT)

Re: Nonideality

Jim -

The explanation of your phenomenon in terms of non-competent monomer seems very
plausible. Expressed proteins frequently contain serious amounts of
mis-conformers (is there such a term ?), and obviously a beautiful SDS-PAGE
pattern gives you no warning of this.

Would not sedimentation velocity be a good (and simple) way of checking this
out ?  As c increases, one would predict a transition to two boundaries,
probably poorly resolved, given the lowish M range, but at the very least a
large broadening should be seen. At a practical level, use of a synthetic
boundary cell would be advantageous here.

Certainly, given how carefully you have checked out things like possible Donnan
effects, I can see no real possibility of a genuine B (Excluded volume) effect.

I look forward with interest to eharing how this problem is resolved. I think
its one we all get stuck with, sooner or later.

All best wishes

Arthur Rowe

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Dr Arthur J Rowe
Director
UK National Centre for Macromolecular Hydrodynamics
Leicester Laboratory
Adrian Building
University of Leicester
Leicester LE1 7RH    UK

Tel: +44 (0)252 3448
Fax: +44 (0)252 5602
ajr@le.ac.uk
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