[RASMB] Overspeeding to establish equilibrium

Peter Schuck pschuck at helix.nih.gov
Tue Jun 25 17:21:01 PDT 2002


Andrew, 

There are rules of thumb (e.g., van Holde and Baldwin 1958, Yphantis 1964).
 One problem is, however, that they don't take into account if chemical
reactions are present which sometimes can be rate limiting.  

If that's not a problem, however, an alternative way is to estimate the
molar mass and the sedimentation coefficient, decide how much sample you
want to use (which will determine the position of meniscus and bottom) and
what rotor speed, and then simply simulate the sedimentation by calculating
the Lamm equation solutions.  Sedfit lets you do that, also the software
Svedberg, and I think also Lamm and Ultrascan, and probably others.  The
advantage of doing it that way is you can also get an idea of the
equilibrium gradient and how much information it contains.

Regards
Peter

van Holde, K.E., Baldwin RL (1958) J. Phys. Chem. 62:734
Yphantis, D.A. (1964) Biochemistry 3:297

At 07:03 PM 6/25/02 +0100, you wrote:
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>Is there a procedure, or rule of thumb, to decide how fast to
>run the AUC to minimise the time taken to reach equilibrium?
>
>I am thinking about unstable samples and how to avoid the long
>delays before reaching equilibrium.
>
>Andrew
>
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