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<TITLE>Re: [RASMB] Analytical Centrifuge Question</TITLE>
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Hi Anna<BR>
<BR>
It is certainly possible to study saccharides in the AUC. I have done it. You will need to observe the following precautions:<BR>
<BR>
(1) a cell blank - always a good thing - is absolutely vital for distributions which are clearly minimal in their range of fringe increment. <BR>
<BR>
(2) a long column will give the best data range. The standard formula (e.g. from BIOMOLS - RASMB archive) gives us around 12 hours equilibration time for a typical saccharide (maltose, D = 42 E-7) if we use a 5 mm column at 20º. You will need to run at the highest speed you can get away with in terms of avoiding window (and hence fringe) distortion. But even being restricted to 40000 things should still be OK<BR>
<BR>
(3) get the concentration up. NO danger of big fringe increments or schlieren effects. Obviously if you are looking for a Ka value then that may influence your choice of loading concentration. In general around 10 mg/ml is a good choice. Of course there is the thermodynamic non-ideality to take into account (which would make an apparent monomer mass around 10% - <I>very</I> roughly - too low). <BR>
<BR>
(4) to cope with estimating Ka in the presence of significant 2BM you can try fixing a pluasible B value in NONLIN (floating both it and K1,2 is a no-no). I had a poster at the recent AUC Meeting in Oxford showing off INVEQ - an algorithm which specifically copes with both Ka and BM as variables.<BR>
<BR>
Good luck! It should work.<BR>
<BR>
Arthur<BR>
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<BLOCKQUOTE><B>From: </B>anna_ber@alcor.concordia.ca<BR>
<B>Date: </B>Tue, 27 Jul 2004 10:01:53 -0400<BR>
<B>To: </B>rasmb@server1.bbri.org<BR>
<B>Subject: </B>[RASMB] Analytical Centrifuge Question<BR>
<BR>
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Hello,<BR>
<BR>
I am working in Dr. Muchalls lab and I have to study a monomer dimer <BR>
equilibrium. I was wondering whether it is possible to study this equilibrium <BR>
with the analytical centrifuge? I have read that molecules as small as sucrose <BR>
have been experimented with in the analytical centrifuge but I have no clue as <BR>
to the lower limit of the apparatus? Is it possible to study a molecule with a <BR>
molar mass of 188.65g/mol and a dimer of 377.3g/mol. <BR>
<BR>
Thank You <BR>
<BR>
Anna Bernardi <BR>
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