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