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<TITLE>Re: [RASMB] time to reach equilibrium</TITLE>
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Perhaps someone could write a nice little app which would continuously monitor at (say) hourly intervals the shift in fringe position at a radial position near to the base of the column, and report back to the screen when this shift either<BR>
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(1) went down to below noise level, or<BR>
(2) failed to do so (i.e. system in some sort of steady state, rather than attaining equilibrium) ?<BR>
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Just to make it nice and easy for folks . . . <BR>
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Arthur<BR>
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Arthur Rowe<BR>
Lab at Sutton Bonington<BR>
tel: +44 115 951 6156<BR>
fax: +44 115 951 6157<BR>
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<B>From: </B>"John Correia" <jcorreia@biochem.umsmed.edu><BR>
<B>Date: </B>Wed, 29 Sep 2004 10:31:11 -0500<BR>
<B>To: </B><strauss@fmp-berlin.de>, <rasmb@server1.bbri.org><BR>
<B>Subject: </B>Re: [RASMB] time to reach equilibrium<BR>
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<BLOCKQUOTE><FONT FACE="Arial">Cheers<BR>
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<FONT FACE="Arial">We published a paper in 1977 that predicted the equilibrium distribution from earlier scans:<FONT SIZE="1"> </FONT></FONT><FONT SIZE="1">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). <BR>
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<FONT SIZE="1">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 <B>must</B> also come from Sed velocity - Sedanal, Sedphat, etc make this very inviting. In our lab sed velocity rules, ie we have no alternative!<BR>
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<FONT SIZE="1">-------------------------------------------------------------------<BR>
Dr. John J. "Jack" Correia<BR>
Department of Biochemistry<BR>
University of Mississippi Medical Center<BR>
2500 North State Street<BR>
Jackson, MS 39216<BR>
(601) 984-1522 <BR>
fax (601) 984-1501 <BR>
email address: jcorreia@biochem.umsmed.edu <BR>
homepage location: http://biochemistry.umc.edu/correia.html<BR>
dept homepage location: http://biochemistry.umc.edu/<BR>
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