n-formyl-methionine true (S)-2-formylamino-4-(methylsulfanyl)butanoic acid N-formyl-L-methionine Residue modification. OBSOLETE remap to MOD:00030. [M:form] 2-formylamino-4-(methylthio)butanoic acid MFM PSI-MI MI:0147 formylmethionine