There could be a number of postranslational modifications, e.g. binding
An excellent resource for this sort of question is the ABRF (Association
of Biotechnology Resource Facilities) e-mail list server. There is a LOT
of mass spec expertise there. Go to this web site,
http://www.abrf.org/ABRF/ListServe.html, to find the rules and address
for posting to that list. If you search the archives for that discussion
I think you will find the URL for a site that lists many, many
modifications as a function of the mass change they induce.
Alliance Protein Laboratories
> Zhang Bo wrote:
>> Dear Netters,
> We have expressed a recombinant protein in E.Coli, and we get the
> purified product. But when we determined its molecular weight by
> MS(mass spectrometry), it has 500 dalton more than expected. Then we
> sequenced the product, its N-terminal sequence and the last two amino
> acid are O.K. So I wonder why?
> Much appreciate any help!