John Philo "jphilo*NO SPAM12*" at earthlink.net
Fri Feb 18 11:55:18 EST 2000

There could be a number of postranslational modifications, e.g. binding
of glutathione. 

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.

Good luck,

John Philo
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!

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