>From what I understand,the oxidation to sulfoxide is reversible,while to
the sulfone it is not.Since you say that you have a monoxidated product,it
should be the sulfoxide.How do you
know that it is monoxidated?The presence of methionine sulfoxide should
move the peptide
to elute before the one with methionine.Of course,you can tell by amino
acid analysis if
you have the sulfoxide or the sulfone.Using the AccQTag method,the
sulfoxide elutes near
Arg,while the sulfone elutes some two minutes later near Ala.
As for back reduction,I have seen several references,using
dithiothreitol,N-methylmercap-
toacetic acid,trialkylphosphines and more.I used to treat peptide which did
not contain
disulfide bond,with dithiothreitol at neutral or higher pH,to see if there
was any shift to
later times(ironically,if there oxidized cysteine,the peak should elute
earlier).There was a bulletin from Applied Biosystem by Cullwell,A. in
1987.Earlier,by Houghton and Li in
Anal.Biochem.vol.98,36-46(1979) described the same fix.I hope that this
will be useful to
detrmine what you have,and how to fix it.If you have the sulfone,you will
be out of luck.
If you have to repeat the synthesis,be extra careful.
Marcus Macht <Marcus.Macht@uni-koeln.de>@aecom.yu.edu> on 06/13/2000
09:37:40 AM
Sent by: Association of Biomolecular Resource Facilities
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To: Recipients of ABRF List <abrf@aecom.yu.edu>
cc:
Subject: Reduction of Met-O?
Dear colleagues,
I currently have a problem with a peptide synthesis, which, more or less,
was quite o.k. The problem I have is related either to a cystein or a
methionin within the sequence (currently I assume a Met-O but will check
this by MS/MS).
A vast amount of the peptide shows up as the monooxidated product, which
can be separated from the reduced product by HPLC. Is there any method to
reduce the Met-O back to Met to get a better yield of the peptide? As far
as my distorted brain can remember, there were some remarks in the recent
discussion about the specific oxidation of Met to Met-O, but I cant't find
it anymore in my mailbox. I have enough material (several mg's) to try a
couple of different methods to get the sulfone back to the thioether.
Any hints or protocols are highly appreciated.
Yours sincerely,
Marcus
********************************************************
Dr. Marcus Macht
Universit”t K–ln
Zentrum f¸r molekulare Medizin
Zentrales Servicelabor
Joseph-Stelzmann-Str. 52
50931 Koeln
Tel.: +49 221 478-6995
Fax: +49 221 478-6977
e-mail: Marcus.Macht@uni-koeln.de
********************************************************
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