Mystery Band

gc genecutl at
Mon Jan 31 06:00:16 EST 1994

	I've been involved in the purification of a protein for crystallography
and have run into something unusual which may cause us problems.

	The protein is expressed in E.coli and run over several columns until
it is pretty much pure.  Sometimes in the E.coli sonicate, the protein
out as a doublet, with a small amount of the protein running slightly
higher than the rest.  Regardless of the initial amount of this higher
form, it invariably increases over time, during the purification and 
especially during storage afterwords (at 4 degrees).  The abundance of
the mystery band increases until it is roughly 50% of the total protein.
We've done some mass spec on the mixture and see only one predominant
mass, with some minor oxidation products (not enough to account for the
mystery band).

	Any ideas?


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