I have two related (general) questions having to do with moderately sized
(10-20) residue tryptic peptides:
1. our impression is that some oxidatation of methionine occurs at some
point after depositing small aliquots (usually <0.1pmol) of methionine
containing tryptic peptides onto MALDI-MS targets and acquiring the
resulting data - has anyone else observed similar phenomenon and/or
investigated it further - are there any pertinent references?
2. does anyone have data relating to the impact of methionine oxidation (to
the sulfoxide) on peptide elution position from C-18 columns that are
eluted with normal acetonitrile gradients in 0.05% TFA (ie., 100 min linear
gradients)? By how much (few minutes?) might oxidation shift a peptide and
would it shift the peptide earlier?
Thanks very much,
Ken Williams
Yale
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