[RASMB] about the small peptide in sedimentation equilibrium

[魏平]

Hi, RASMB members,

I am studying a protein with monomer-dimer equilibrium.
As a novice in the AUC area, so many problems has troubled me.
And our lab's this XL-A instrument is the first one in our college, even

in the whole China, so I can only got very limited experienced advice 
from BECKMAN's trainer. So I have to ask for help through the "google"
then, I found Prof.Stafford's lab, found this email forum.

After learning the RASMB's mailing archives, I has got 
the point to avoid the nonspecific aggregation of my reducible
protein by flushing nitrogen to the sample cells.

But, when I strictly repeated my equilibrium constant determination
experiments,
I always got diffrent results ranging greatly from 20 uM to 100 uM. I
don't know
whether it's a reasonable fluctuation. I have tried diffrent
concentrations and 
rotator speeds.

In addition, I am studing how an octapeptide (MW: 900 kD) affect the
protein's
equilibrium. Briefly, in a sample cell, octapeptide and protein
(mol:mol=1:500) 
was mixed and a same concentration's octapeptide solution as reference.
The 
question is :

1, Can I simply treat the octapeptide as one of the buffer components ?
(the peptide can associate with monomer as a competitive dimer
inhibitor)

2, How to calculate the density, viscocity and the partial specific
volume in such a "high" concentration peptide solution.

3, Can any of you recommend some good published examples similar to
mine? I have tried my best to look for some.

Appreciated for all your patience and kindness!

Best wishes,
Weiping
__________________________________________
Institute of Physical Chemistry, room 116
College of Chemistry, Peking U
Peking, 100871
P.R. China
Phone: 86-10-62756833
Fax:   86-10-62751725
__________________________________________