From: Arthur Rowe <Arthur.Rowe@nottingham.ac.uk>
  To  : Marina Mapelli , rasmb@bbri.harvard.edu
  Date: Tue, 13 Apr 1999 11:01:40 GMT0BST

Re: ultracentrifuge data analysis

Dear Marina

The most likely reason for the deviation you observe would appear to be that the 
vbar value of your protein in the presence of 20% glycerol and 300 mM NaBr is 
higher than the one you have used.  How have you determined vbar - from the 
sequence by computation, I guess ?

There is no literature that I am aware of that gives values for vbar in this type of 
solvent, and I suspect that you do not have enough material to do an actual 
determination (not a nice experiment to do in any case, in that viscous solvent). 
There is a hand-waving explanation of your vbar being higher than expected, in 
terms of both glycerol and that (fairly concentrated) NaBr stripping off water of 
hydration and hence much diminishing solvent striction. The trouble is, that a 
quick calculation suggests only around an 8% increase in estimated M from this 
effect, which is not enough to account for your difference.

However - I would like to know what value of vbar was used and how it was 
derived before saying anything more !

Best wishes

Arthur Rowe
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