From: John Correia <jcorreia@biochem.umsmed.edu>
  To  : rasmb@alpha.bbri.org
  Date: Sat, 20 Mar 1999 17:33:33 -0600

Re: Concentration units when fitting equilibrium data

Jo

While I cannot speak for the Beckman version of anything, Nonlin uses a
monomer to n-mer formalism in the units of detection, absorbance or
fringes.  When you plug in the conversion to molarity (for example C(M)
= OD/l*extinction where l = 1.2 cm and yes the dimer is assumed to
have twice the value unless you know otherwise) you get an equation that
has been described repeatedly (see for example CORREIA,J.J., S.P. Gilbert,
M.L. Moyer and K.A. Johnson (1995)   "Sedimentation Studies on The Kinesin
Head Domain Constructs K401, K366 and K341.  Biochemistry, 34, 4898-4907.)
as K2 (M-1) = K2(Abs-1) * (1.2*extinction/2).  Equation for trimer and
tetramer, etc follow accordingly.

There has been much complaining that the software doesn't give you the
answer in the correct units and that the non-expert has to calculate it -
dare I say even I calculate it - of course if the Beckman version attempts
to give you M-1 and screw up tell us!!!

-------------------------------------------------------------------
 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                             
 new email address: jcorreia@biochem.umsmed.edu     
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