Sandy,
like mentioned previously, sounds like FeS.
record an optical spectrum. Or even better, check whether there is
somebody on the campus running an EPR machine (equipped for helium
temperature measurements)
Maybe a new FeS protein? FeS is not necessarily required as redox
cofactor. It can have any other function . See e.g. primase from
eukaryotes (recent structures)
Or in your native (maybe eukarytic) protein is a Zn. E.coli places
sometimes a FeS instead of a Zn in the site.
Less likely but further possibility: Ni2+ bound to the protein. If DTT
is added: Ni2+ -S coordinated is not redox stable and oxidizes to Ni3+
(brownish colour).
HTH
Guenter
Dear all,
I have purified protein from E.coli. expression system. the protein
has been purified with three independant columns. Now during
concentration step using amicon, the protein shows brown colour. what
could be the reason.
best regards and Thanks,
sandy
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