ProtSeq and MS: Prot modification

Barbara J. Root (Barbara_J._Root@ccmail.bms.com)
Tue, 28 Jul 1998 09:08:12 -0400

I would like to see if anyone has observed a modied methione which I
may be seeing. In a recent peptide map, a new peak was observed.

Analysis by protein sequencing shows very low amount of a known
peptide sequence but with low amount a methionine (8-10 x less than
expected) at its one site of occurrence. At that site there was no
other peak of the height of the rest of the sequence, although there
was a small amt of a peak at PTH-ILE and a slight increase in dmptu.

MALDI MS shows the mass anticipated minus 48 daltons. Further
fragmentation confirms the mass change to be at the site of
methionine.

Here is my question: has anyone had experience with a methionine
degrading to dehydroamino butyric acid? Any other thoughts?

Thanks for your help!

Barb Root
Bristol-Myers Squibb
Syracuse NY