[RASMB] Theory of S moments

John Correia jcorreia at biochem.umsmed.edu
Wed Feb 8 08:34:25 PST 2006


Sorry for being late in sending this email - I misplaced my ET Adams
folder & wanted to be sure I knew what moments were discussed in his
papers.  I discuss these papers in my 2000 weight average review.  These
papers present the theory of using sn, sw and sz for self associating
systems.  Historically they fall into the category of graphical
techniques that dominated the analysis of data in the 70's, especially
equilibrium data.  They are probably most useful for model building and
parameter estimation but on a system by system basis they should give
the same answers as direct boundary fitting.
 
I would like to revive a suggestion made by Allen Minton last year that
we create an Online Library of old papers.  I am sure there are legal
issues, but for example my library does not have the volumes these
papers came from, I had to use interlibrary loan, and the 1973 paper
doesn't even show up in a PubMed search.  Walter has set up a classic
papers folder on RASMB, the format of which is not yet decided, although
it is searchable through the RASMB search engine.
 
http://rasmb.bbri.org/rasmb/classic_literature/
 
Weirich CA, Adams ET Jr & Barlow GH (1973) Bioiphys Chem 1, 35-45
(1973)  Sedimentation coefficients of self-associating species.  I. 
Basic Theory
 
Abstract:  Under the same solution conditions, the apparent weight
average sedimentation coefficient, swa, and some quantities obtained
from it can be combined with the equilibrium constant or constants , Ki,
and the monomer concentration, c1, obtained from sedimentation
equilibrium, light scattering or osmotic pressure experiments on the
same self-associating solute, so that the individual sedimentation
ceoefficients , si, of the self-associating species, and also the
hydrodynamic concentration dependence parameter, g or gs, can be
evaluated.  Using two different models for the hydrodynamic
concentration parameter, four different methods are presented for the
evaluation of si's.  Methods for evaluating g or gs, once the si's are
known, are presented.  A method for obtaining the number average
sedimentation coefficient, Sn, and its application to self-association
is presented.  Methods are shown for the evaluation of z average
properties, Xzc, as well as number average properties, XNc, of a
self-associating solute from its weight average properties, Xwc.
 

Beckerdite JM, Weirich CA, Adams ET Jr, Barlow GH.  Biophys Chem. 1983
Apr;17(3):203-10.  Sedimentation coefficients of self-associating
species. II. Tests with a simulated example and with beta-lactoglobulin
A.
 
Abstract:  If sedimentation equilibrium and sedimentation velocity
experiments are performed on a self-associating solute under the same
solution conditions, it is possible to evaluate the sedimentation
coefficients (si) of the self-associating species and the usual
concentration dependence parameter (g or gs). We have tested some of
these methods with simulated examples. A more critical test is to use
real data. Sedimentation equilibrium experiments with beta-lactoglobulin
A at 20 degrees C in 0.2 M glycine buffer (pH 2.46) indicated that a
nonideal monomer-dimer association was present. Sedimentation velocity
experiments were performed on beta-lactoglobulin A under the same
conditions. Using data from both sets of experiments we were able to
evaluate s1, s2, g and gs using two different models for swa, the
apparent weight average sedimentation coefficient. The empirical model
for swa developed by Weirich et al. [1] gave better variance than did
the model for swa developed by Gilbert and his co-workers [2-5]. Using a
simulated monomer-dimer association mimicking a system having higher
sedimentation coefficients than beta-lactoglobulin A did, we were able
to show that one could not obtain s2 from tangents to the plot of 1/swa
vs. c in the high concentration region. The methods developed here for
sedimentation coefficients can be applied to other experiments in which
a weight average property (or its apparent value) of a self-associating
solute is measured, provided the appropriate thermodynamic experiments
are done under the same solution conditions.  


 
-------------------------------------------------------------------
 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                             
 email address: jcorreia at biochem.umsmed.edu     
 homepage location: http://biochemistry.umc.edu/correia.html
 dept homepage location:    http://biochemistry.umc.edu/
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