Angela-
Many years ago, I was able to very effectively concentrate a protein by dialysis against a 10% solution of high molecular weight polyethylene glycol. Unlike sucrose, the PEG was just too big to diffuse through the pores of the membrane.
Another low-tech method of concentrating a protein is to pack the dialysis tube (containing the protein solution) in dry sephadex. The sephadex will "trap" the water diffusing through the membrane pores, thereby concentrating the protein.
Vernon
Vernon A. Shoup
Regeneron Pharmaceuticals
Rensselaer, NY 12033
(518)488-6012
vernon.shoup@regpha.com
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Date: 11/04/1998 5:17 PM
From: Angela c. Murphy
I too have gotten brown gunk (tar, caramel) from hydrolyzing sugar-
containing peptides or proteins, but have found that the interference with the amino acid analysis really depends on how much carbohydrate is
there. I routinely do analyses for another lab that does NMR studies of
DNA-binding proteins, and I am often given a sample of a protein which
has the DNA bound. These samples do not give any brown or even yellow
color upon hydrolysis and the analyses are very reproducible. On the
other hand, people in my own lab have given me protein samples that were
concentrated by dialysis against sucrose - very messy. The sucrose apparently gets through the membrane somehow, perhaps by dissolving in
the water it is supposed to remove. Has anyone else encountered this
problem and found a way to get rid of sucrose before hydrolysis?
Angela C. Murphy