From: Thomas M Laue <tml@christa.unh.edu>
  To  : RASMB group <rasmb@bbri.eri.harvard.edu>
  Date: Tue, 24 May 1994 13:09:29 -0400 (EDT)

More V-bar stuff

Dear Jack and John- The errors are found using calculated vbars. The
errors are close to 10-15% in Mr. I have always been able to rationalize
errors in vbar in the other direction by taking account of the charge on
the molecule. From the sounds of it, the disulfide theory is pretty lame.
The coagulogen has 8 disulfides and a molecular weight of 19,670. On
sedimentation it gives an apparent Mr ~16,300. Buffer doesn't seem to be a
major factor, since the same error appears in Tris-saline or 6 M
guanidine. We have not been able to fully reduce the protein (or so it
seems from gels) so I am not comfortable saying whether or not the error
is reduced when the disulfides are reduced. The protein is otherwise
"normal" with respect to composition, charge and the like.

Preston mentioned that Ab gives approximately the same level of error. 
What mechanism would produce such an underestimate of vbar. It is easy to 
rationalize electrostriction causing an overestimate. It would be 
interesting to know what the hydration of this molecule is like.

Thanks for your responses, and I am looking forward to hearing more.
Tom