From: E.braswell <BRASS@UCONNVM.UCONN.EDU>
  To  : rasmb@alpha.bbri.org
  Date: Wed, 26 Apr 00 12:53:43 EDT

variation of local lnks

Borries and others; We have frequently run into this situation.  Do you
notice that there is a trend in the values of lnK, in that they increase
in a positive direction as loading concentration decreases? If so, that
is probably due to the presence of incompetent species, not only monomer.
Irreversible species can be any size--but usually we have found that
they are at the high end.  Of course it could also be an impurity with a
MW not related to any of the species that you are trying to fit.
The best fitting procedure is to solve your
model so that you are fitting globally all but the last step of the
association sequence.  Then let that step be fit globally followed by
letting that step be fit locally.  Then compare rms and systematic errors.
There are attempts being made to get info re: the species that is incompetent
and what fractional concentration is present.  Yujia Xu, Dave's last student
has a dissertation devoted to this which I hope will be published soon.
You could play around with it in a similar way by simulating various mixtures
of incompetent species, and seeing what Nonlin will do. Hope this helps.
                                                        Emory

Emory H. Braswell
Professor of Biophysics and Head,
National Analytical Ultracentrifugation Facility
U-149
University of Connecticut
STORRS, CT 06269-3149
TEL 860 486 5032
FAX         5005
E.BRASWELL@UCONN.EDU