From: E.braswell <BRASS@UCONNVM.UCONN.EDU>
  To  : RASMB@bbri.org
  Date: Fri, 15 Oct 99 21:32:37 EDT

Re: sedimentation equilibrium runs at high salt concentrations

Dear Dr. Gunther Stern,  First, the diffusion constant doesnot
affect the apparent MW, only the time to reach equilibrium.  Second, if you did
not run it at a high enough speed, you might get an ideal single species fit.
You should be spinning a 2.5 mm column at about 20k in order to get enough
information from the curvature of the gradient. Third, you should do
3 loading concentrations, approx. 3 fold different in concentration and at
two speeds (say 20 and 30k).  This should give you more diffinitive results.
You did not say how heavily charged your material is, or why you want to run it
at such a high salt concentration.  If it is because of charge and you have an`
associating system it gets complicated.  Then the question is, did you follow
the Ehrenberg technique of dialyzing and doing densities on the material? This
has been discussed before on this forum--so I won't bore you. Best Wishes,
Emory

Emory H. Braswell
Professor of Biophysics and Head,
National Analytical Ultracentrifugation Facility
U-149
University of Connecticut
STORRS, CT 06269-3149
TEL 860 486 5032
FAX         5005
E.BRASWELL@UCONN.EDU