From: Marina Mapelli <Marina.Mapelli@EMBL-Heidelberg.de>
  To  : rasmb@bbri.harvard.edu
  Date: Mon, 12 Apr 1999 17:06:34 +0200 (MET DST)

ultracentrifuge data analysis

Dear collegues,
I'm currently working on the characterization of a single-stranded dna
binding protein. I'm trying to understand the
behaviour in solution of  different mutats using analytical
ultracentrifugation. My equilibrium experiments result in a monodisperse
preparations but the mono fitting leads to  molecular
weights too small comapared with the ones predicted by the sequence and
observed in denaturing gel runs (85-90 KDa instead of 120 KDa).
My experiments take place in a buffer containing 20% glycerol and 300mM
NaBr. I measured the density of the medium, but I'm wondering whether and
how the partial volumes of the protein can be affected by the buffer. Or
whether there's another explanations for this behaviour.
 
I also noticed that sometime I got a good fit with a biexponential fitting
but with Mw that are one too small and one too big. Does this means that
 protein aggregation is taking place so that the bimodal fit
is not valid (I know that protein-protein intercations exist)?


many thanks in advance
best regards
marina


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 Marina Mapelli
 EMBL Heidelberg
 Meyerhofstrasse n.1
 D69012 Heidelberg
 Germany

 e-mail:	mapelli@EMBL-Heidelberg.de 
 tel: 	     	+49 6221 387567
 fax: 		+49 6221 387306

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