Regardless of which (if either) explanation is correct, the next question
is how does CH3-SH eliminate from the peptide? Normally this only occurs
if the sulfur is first activated by conversion to a sulfonium ion (positive
charge on S), for example by treatment with cyanogen bromide or an
alkylating agent such as iodoacetamide. Has the peptide been treated with
alkylating agents? If it is a naturally occuring peptide (not synthetic),
maybe it arises from a post-translational modification of sulfur.
It's an interesting problem.
Richard Laursen
--------------------------------------------
> 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
Richard A. Laursen
Department of Chemistry
Boston University
590 Commonwealth Ave.
Boston, MA 02215
Tel (617) 353-2491; FAX (617) 353-6466
email: <laursen@bu.edu>