From: Bethell, Sue S <ssb25133@glaxowellcome.co.uk>
  To  : rasmb@alpha.bbri.org
  Date: Wed, 24 Nov 1999 15:50:10 -0000

Another what is going on?

Dear all,

Have any of you had any experience with proteins that precipitate when they are agitated?  I don't mean the good old reliable 'bubble test' (if the solution froths there is protein in there).  

This protein precipitates out when it is left GENTLY rocking or stirring even after a couple of hours.  Dialysis has to be done over extended periods without stirring.  It also does not like freeze-thawing, as it precipitates upon thawing even in the presence of 30% glycerol.  

I am running a velocity sedimentation experiment at the moment:  the MW of the protein by sequence and mass spec is 37KD.  I am running it at 40000rpm in 10% glycerol 4C.  Concentrations in absorbance units at 280nm are 1.2, 0.7 and 0.4AU.  The protein has just about cleared the meniscus after 4.5 hours.  I know that glycerol slows things down due to viscosity and all but this really slow.

Anybody know what may cause a protein to precipitate when shaken or stirred and why it may be so slow to sediment?   Shape?

Thanks in advance for any suggestions!!!!

Sue 

Sue Bethell
Protein Technologies
Protein Science Unit			
GlaxoWellcome R&D
Gunnelswood Road						
Stevenage 
Herts. SG1 2NY
UK

email: ssb25133@GlaxoWellcome.co.uk
tel:  (44) (0)1438-763419
fax: (44) (0)1438-764865