From: Dr A.J. Rowe <ajr@leicester.ac.uk>
  To  : rasmb@bbri.harvard.edu
  Date: Mon, 6 Nov 1995 12:36:16 +0000 (GMT)

non-ideality

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 hearing how this problem is resolved. I think
  its one we all get stuck with, sooner or later.

  All best wishes

Arthur Rowe

***************************************************
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
***************************************************