[RASMB] 1290 Daltons

[Lustig]

Dear colleagues, dear  Erin Matthews,
I don't know neither your 12.90 Kda peptide, nor the used buffer and sure 
not  the  V-bar, that must not be
as the calculated one for hydration and other unknown effects solvent 
dependent. I mentioned this because you wrote that 13.32Kda is a much too 
high  value! (I would  claim  that is  a very good result if
it takes in consideration concentration dependence non idealities self 
association etc...)
The speed 60K rpm chosen is perfect for  the  highspeed/meniscus depletion 
mode . As you well said ,
samples with normal  diffusion behavior will not deplete complete, so all 
your information is concentrated
in a very short radial part  near the cell bottom and  becomes relative 
high  concentrated what can  mean nonidealities or self association.
 From  my  experience , we have always  to proof  if a certain result is 
constant  at  various  concentrations  or only a part  of  a 
self-association row of  increasing  values where the zero extrapolated 
value is the  right one or  a certain plateau at higher concentrations that 
indicates  that the
lower values are dissociation products  of a certain  complex (or an active 
dimer for  example).
I prefer  to run at low /conventional speeds at few  concentrations and 
speeds that already will alarm you
I you deal with a perfect  single species.

We use a program  called  Segal . You may read  carefully  the description 
and examples, and even
load  the program down for use from the net.

http://www.biozentrum.unibas.ch/personal/jseelig/AUC/index.html

yours ... ariel

  Lustig Ariel
Biozentrum der Universität Basel
Klingelbergstr. 70
CH 4056 Basel
Switzerland
Dept. of Biophysical Chemistry  /
Analytical Ultracentrifuge Lab.TEL....+61 2672187
                                             Fax    +61 2672189
E-mail   Ariel.Lustig at unibas.ch