derives from cyclized residue modified L-methionine residue protonated L-methionine (L-methioninium) residue dehydromethionine (from L-methioninium) (3S)-3-carboxy-1-methylisothiazolidin-1-ium -2.0161991119384765625 -2.0199999809265136719 1+ 131.0399322509765625 131.19000244140625 A protein modification that effectively converts an L-methioninium (protonated L-methionine) residue to dehydromethionine. C 0 H -2 N 0 O 0 S 0 C 5 H 9 N 1 O 1 S 1 L-dehydromethionine MOD:001464 MOD:01907 N-term PSI-MOD This process accounts only for cyclizaation and not protonation. The alternative process (MOD:01906) accounts for both protonation and cyclization. artifact