How did you determine the mass of the peptide? We have observed that
Trp-containing peptides analysed by madli in alphacyano-4-hydroxycinnamic
acid can often give +32amu peaks. If the sample is reanalysed by using
sinapinic acid, the +32 peak disappears, confirmed by esms. A cautionary
note before assuming that there is really an oxidation present.
Len
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Dr Len C. Packman
Assistant Director of Research
Protein and Nucleic Acid Chemistry Facility
Department of Biochemistry
University of Cambridge
80 Tennis Court Road
Old Addenbrookes Site
Cambridge, CB2 1GA, UK
Tel: +44 (1223) 333639
FAX: +44 (1223) 766002
e-mail: lcp2@mole.bio.cam.ac.uk
Visit my WWW page at http://www.bio.cam.ac.uk/proj/adr/PNAC/pnac.html