[RASMB] time to reach equilibrium

[John Correia]

Cheers
 
We published a paper in 1977 that predicted the equilibrium
distribution from earlier scans: J.J. CORREIA, G.H. Weiss and D.A.
Yphantis (1977). "An Extrapolation Method for Reducing Equilibrium Times
in Sedimentation Equilibrium Systems,"  Biophysical J. 20, 153-168.  The
point being, as Holger just mentioned, many samples aggregate with time,
or display insolubility, instability.  Many of us have observed this
with proteins like tubulin which like to associate in polymorphic forms,
and with many His tagged proteins.  In many of these cases there is a
slow loss of material from a "stable" exponential distribution. 
Information can still be extracted, with caution.  Solutions to this
problem have included change the pH, ionic strength, etc (obvious), drop
the temperature, add reducing agent (TCEP has worked best in limiting
cases), remove the His tag, go to a short column format (which speeds up
the time dramatically (16-fold for a 4-fold reduction in column height).
 
 
I not only agree with Bo, I insist that you do Sed velocity before you
waste time doing sed equilibrium - I suspect most people do this -
furthermore for many systems the quantitative analysis must also come
from Sed velocity - Sedanal, Sedphat, etc make this very inviting.  In
our lab sed velocity rules, ie we have no alternative!

 
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 Dr. John J. "Jack" Correia
 Department of Biochemistry
 University of Mississippi Medical Center
 2500 North State Street
 Jackson, MS  39216
 (601) 984-1522                                 
 fax (601) 984-1501                             
 email address: jcorreia at biochem.umsmed.edu     
 homepage location: http://biochemistry.umc.edu/correia.html 
 dept homepage location:    http://biochemistry.umc.edu/ 
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