IDENTIFICATION OF L-METHIONINE OXIDATION-PRODUCTS IN TRIPEPTIDES, IN MET-ENKEPHALIN AND IN THE BOVINE BASIC PANCREATIC TRYPSIN-INHIBITOR H-1 AND C-13 NMR-STUDY

L-methionine (Met) oxidation products in tripeptides, in Met-enkephali n and in the bovine basic pancreatic trypsin inhibitor have been ident ified by H-1 and C-13 NMR spectroscopy. The oxidation of Met residues by stoichiometric amounts of chloramine-B, H2O2 and I-2 yields a mixtu re of L-methionine sulfoxide (Met(O)) and dehydro-L-methionine (DH-Met ), Met(O) and DH-Met, respectively, at pH 7.0 and 25.0 degrees C. The formation of DH-Met occurs only if the amino-group of Met is not deriv atized. The analysis of H-1 and C-13 NMR spectra allows us to quantita te Met oxidation products, to ascertain the relative proportion of the R and S forms of MET(O) and DH-Met, and to reveal the presence of a M et residue at the N-terminal position in peptides and proteins.