CNBr digestions in formic acid result in formylation of Ser and Thr. Using
70% TFA instead of formic acid eliminates the +28's. See
D. R. Goodlett, R. B. Armstrong, R. J. Creech, R. van Breemen, Anal.
Biochem. 186: 116-120 (1990) "Formylated peptides from cyanogen bromide
digests identified by fast atom bombardment mass spectrometry."
Martha
Martha M. Vestling, Ph.D.
Director of Mass Spectrometry
Department of Chemistry
University of Wisconsin - Madison
1101 University Avenue
Madison, Wi 53706
608-262-3449, FAX 608-262-0381
vestling@chem.wisc.edu