Hello Markus,
the split of of 64 Da is to my experience a cleavage of CH3-SHO from the oxidized Methionine. I saw it quite regular in spectra from tryptic in-gel digests at CID experiments on a QTOF instrument in Cologne.
To verify this, you should look if only fragments containing the Met(O) are affected by the loss of 64 Da.
Yours sincerely,
Marcus
--------------------------------------------------------------
Dr. Marcus Macht
Applikation und Support Proteomics
Bruker Saxonia Analytik GmbH
Permoser Str. 15
04318 Leipzig
Germany
Tel.: ++49/341-2431-465
Fax: ++49/341-2431-404
email: mma@bsax.de
>>> Markus Piotrowski <Markus.Piotrowski@ruhr-uni-bochum.de> 19.02.2001 20.51 Uhr >>>
Dear All,
I sequenced a peptide (mz 574, doubly charged) by ESI-Q-TOF-MS with the
sequence: GQADTIGIAMR (Methionine oxidized)
Interestingly, I can also read part of the sequence with peaks having a
mass -64. Anyone heard about a loss of 64 during fragmentation of
peptides?
The centered spectrum is attached as simple text file.
Markus
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