[RASMB] peak in sedimentation velocity scans at high protein conc.

[Tom Laue]

Hi all,
Andy, Jack and John are right. This is a schlieren phenomenon, and is a 
consequence of the gradient in refractive index (gradient in 
concentration), and not the concentration per se. The early XLAs had a 
shorter "snout" on the slit assembly and the schlieren peaks were a 
common feature. This problem was rectified by Beckman very early on (by 
machine #11, I think). Arthur Rowe, Steve Harding and Helmut Colfen used 
the schlieren peak to get S for a polysaccharide sample as I recall.
In any case, your best option is to analyze data where the gradient has 
diminished sufficiently for the peak to disappear. If this does not 
occur, it would suggest that your sample has a large amount of 
hydrodynamic nonideality (i.e. a graph of s versus c has a steep 
negative slope). Depending on what question you are addressing, you may 
not be able to answer the question readily by sedimentation velocity.
Best wishes,
Tom

Norbert Muecke wrote:

>Hi,
>I have done some velocity runs at high protein conc. (up to 6g/l).
>A new peak within the boundary could be observed.
>I have attached the scans of three different concentrations.
>Absorbance was measured at 284nm.
>Any idea of how to explain that phenomena would be appreciated.
>
>Best regards
>Norbert
>
>
>Division Biophysics of Macromolecules, B040
>German Cancer Research Center (DKFZ), TP3
>Im Neuenheimer Feld 580
>D-69120 Heidelberg, Germany
>
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-- 
Department of Biochemistry and Molecular Biology
University of New Hampshire
Durham, NH 03824-3544
Phone: 603-862-2459
FAX:   603-862-0031
E-mail: Tom.Laue at unh.edu
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