From: John Correia <jcorreia@biochem.umsmed.edu>
  To  : Jim.Bloom.B@bayer.com
  Date: Mon, 08 Nov 1999 13:34:16 -0600

Re: Simulating Eq curves and Re: cavities

Jim

I realize there is an emerging field that applies MS to interacting
systems, but my reading is it works well for very tight association or
very slow kinetic systems.  Does it in fact work for weak (10>5 to 10>7) &
rapiding reversible associations?  

The specific paper you mention observes a complex with and without water. 
However, there must be a difference between bound water/bulk water
interactions,  bound water/release to a vacumn and tightly bound water at
an interface trapped in what is now a trapped complex.  At the very least
there is a surface contribution in the second & third case that is
different.  These are also clearly not equilibrium experiments since the
structures of the complexes must depend upon the solvent; the absence of
water must eventually lead to changes in folding.  And as this paper
points out electrostatic interactions in a vacumn are very different from
in solution.

I agree many methods must be brought to bear, but it strikes me that the
info MS would provide here is 1:2 vs 2:1 of the largest complex.  The
reponse I have to Arturo's request is what is the estimated Kd and are you
sure the low MW isn't simply because you are below saturating
concentrations; ie it is not a tight complex at stoichiometric ratios.  If the
affinities are not tight then the measured MW will never be the complex MW
because free or excess reagent lowers the overall MW.  What do you see in
a sed vel run?  Does everyting runs as a complex?

-------------------------------------------------------------------
 Dr. John J. "Jack" Correia
 Department of Biochemistry
 University of Mississippi Medical Center
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