PEG-Protein analysis, Capillary electrophoresis

John E. Wiktorowicz, Ph.D. johnw at nospam.lynxgen.com
Mon Mar 29 16:25:53 EST 1999

weijunli wrote:

> I research about the modification of BSA and Bovine Hb with PEG5000. But I
> haven't find good method to indentify the modification degree of the
> PEG-Protein. Would you give me some suggestions or references,especially the
> capillary electrophoresis method?
> thanks!
> Weijun Li

How accurately do you need to know the degree of substitution? You might get a
general idea by using capillary electrophoresis-based SDS analysis. The problem
is that PEG5000 represents a wide distribution of PEG molecular weights
centered around 5k. That means that your peaks (from multiply modified
proteins) may not be adequately resolved to permit identifying the degree of
substitution. It may be worth a try though. Don't forget that PEG will not
adsorb SDS, and so the underlying assumption of protein MW estimation may not
apply; i.e., that proteins adsorb about 1.4 g SDS/ g protein. In this case the
value will be less. This means that you'll have to perform a Ferguson analysis
(Rel migration vs [gel]). In addition the PEG may change the overall shape of
the SDS-laden protein (from ellipsoid) from the standards. All this is to
prepare you for the large error you'll experience in your analysis. You might
be better off using MS, but this is far from a sure thing (especially at MW's).
Good luck.
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