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<DIV><SPAN class=359040118-14102002><FONT face=Arial>Good afternoon,
everyone.</FONT></SPAN></DIV>
<DIV><SPAN class=359040118-14102002><FONT face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN
class=359040118-14102002> <FONT
face=Arial>I have a system that appears to have two species in it when the
velocity data is modeled with SedFit, one at 4.0 S (monomer) and the
other at 5.5 S (dimer). Velocity data collected at different
concentrations do not seem to indicate a reaction boundary.
Based on the peak heights and areas from the c(S) distribution, the
dimer is 14 times higher than the monomer.</FONT></SPAN></DIV>
<DIV><SPAN class=359040118-14102002>
<FONT face=Arial>Recently, I have been trying to fit equilibrium data with
Nonlin to confirm the molecular weight of the two species and determine the
equilibrium constant. I have a large range of concentrations (1.0 mg/ml to
0.015 mg/ml) and many rotor speeds (4K to 40K). I have tried different
scans in the fitting routine, but I can't seem to fit the data
without nonrandom residuals. Some of the residuals indicate
nonideality, some indicate reversible association with n=2, and some indicate
aggregation. These residuals are all when trying to fit to a 1-2
system. I will add that even fitting single data sets (3 concentrations, 1
speed) show similar residual patterns as for the global fitting when fitting to
a monomer system; single sets do not fit to a 1-2 system.
</FONT></SPAN></DIV>
<DIV><SPAN class=359040118-14102002>
<FONT face=Arial>Some of my parameters: sigma is calculated and held
constant. DeltaY is set to 0, then allowed to float after first "fit", LnA
starts off at 3, and I set LnK2 to -1, N2 floats. </FONT></SPAN></DIV>
<DIV><SPAN class=359040118-14102002>
<FONT face=Arial>I realize I may have left out pertinent info, so please let me
know if more is needed. I am wondering if I am missing something with the
program or the concentrations or the speeds... Any advice would be appreciated,
as I have struggled with this problem way too long. Thank you very
much.</FONT></SPAN></DIV>
<DIV><SPAN class=359040118-14102002><FONT face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=359040118-14102002><FONT
face=Arial>Sincerely,</FONT></SPAN></DIV>
<DIV><SPAN class=359040118-14102002><FONT face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=359040118-14102002><FONT face=Arial>Cheryl</FONT></SPAN></DIV>
<DIV><SPAN class=359040118-14102002><FONT face=Arial></FONT></SPAN> </DIV>
<DIV> </DIV>
<DIV>******************************</DIV>
<DIV>Cheryl A. Blasie, Ph.D.</DIV>
<DIV>Centocor</DIV>
<DIV>200 Great Valley Parkway</DIV>
<DIV>Malvern, PA 19355</DIV>
<DIV> </DIV>
<DIV>Mail Stop M-1-6</DIV>
<DIV>Phone: 610-889-4447</DIV>
<DIV>FAX: 610-889-4771</DIV>
<DIV>******************************</DIV>
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