menadione quinone derivative modified L-cysteine residue menadione quinone derivative - site C 170.036773681640625 170.160003662109375 273.04595947265625 273.30999755859375 PSI-MOD C 14 H 11 N 1 O 3 S 1 Menadione MOD:01466 modification from Unimod Chemical derivative C 11 H 6 O 2 C artifact none Menadione quinone derivative