From: Thomas M Laue <tml@christa.unh.edu>
  To  : C.S.RAMAN <raman@bioc01.uthscsa.edu>
  Date: Thu, 26 May 1994 09:50:14 -0400 (EDT)

Re: V-bar

Hello-
A couple of comments for the discussion on v-bar-
The effect of electrostriction on v-bar has been examined. This pushes 
v-bar down, giving rise to an overestimate of the Mw. A discussion of 
this can be found in McMeekin and Marshall (1952) Science 116:142-143 and 
Kharakoz, D.P. (1989) Biophys. Chem. 34 115-125. The latter paper 
provides corrections to the v-bar of charged amino acids. We have used it 
with highly charged peptides [Starovasnik, et al., (1992) Biochemistry, 31 
9891-9903] and it seems to work rather well. 

As for the temperature dependence of v-bar, Durschlag's article [in
Thermodynamic Data for Biochemistry and Biotechnology, Springer-Verlag
(1986), p. 62] indicates that the temperature dependence is 2.5-10x10^-4 
cm^3/g/K, with most lying between 3.5 and 5 x 10^-4.

With regard to the apparent underestimate of v-bar, David Yphantis 
recalls an article by David Waugh (ca. 1955) in which it is proposed that 
packing of helices can result in voids that are large enough to affect 
v-bar, but are too small to accomodate water. This provides a simple 
mechanism for the observed error in v-bar, and correlates rather well 
with the molecules that seem to have this problem (i.e. very compact and 
stable). I will try to hunt down the reference.

Best to all-
Tom Laue