[RASMB] Fw: Can 0.25M of NaCl take care of nonideal behavior of a protein?

[Yun-Ru (Ruby) Chen]

----- Original Message ----- 
From: Yun-Ru (Ruby) Chen 
To: rasmb at rasmb-email.bbri.org 
Sent: Friday, May 31, 2002 2:37 PM
Subject: Can 0.25M of NaCl take care of nonideal behavior of a protein? 


Dear RASMB members:
              I have currently run into problems by analyzing my data from sedimentation equilibrium studies. I am very confused and frustrated about it.
I hope if any of you can give me some ideas. I am working on a 10KDa protein domain which is suppose to be a helical bundle. The pI of the protein is calculated to be about -1.5 at pH 8. I have ran the samples in two different buffers, one in 30 mM Tris, pH8, and one in Tris with 250 mM NaCl. Both buffers contain 0.2mM DTT and are at pH 8. However, we cannot fit all the data to a single assembly model. I have tried to put in different guesses of "B" values for nonideality, but the fits are even worse. Moreover, the data from the salt buffers look better then the one without. Therefore, does that mean 0.25M NaCl is not enough or there is something else that I should be aware of? My protein is much less soluble in the presence of NaCl, so it is a bit hard for me to increase to salt concentrations.
Thanks very much if you can share your idea with me.

Sincerely, 
Ruby

Yun-Ru (Ruby) Chen
Ph.D. candidate
Department of Structural and Molecular Biochemistry
North Carolina State University
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