L-methionine sulfoxide L-methionine (S)-sulfoxide 147.035400390625 147.19000244140625 15.994915008544921875 16.0 A protein modification that effectively oxygenates an L-methionine residue to L-methionine sulfoxide S-diastereomer. C 0 H 0 N 0 O 1 S 0 C 5 H 9 N 1 O 2 S 1 M MOD:00721 MOD_RES Methionine (S)-sulfoxide PSI-MOD S-MetO artifact uniprot.ptm:PTM-0481