FAD modified residue modified L-cysteine residue S-(6-FAD)-L-cysteine 783.1414794921875 783.530029296875 886.15069580078125 886.67999267578125 MOD:01146 From DeltaMass: Average Mass: 784 with no citation. This modification has not been reported [JSG]. none C 27 H 31 N 9 O 15 P 2 FAD hypothetical S6FADCys C PSI-MOD C 30 H 36 N 10 O 16 P 2 S 1 A protein modification that effectively converts an L-cysteine residue to S-(6-FAD)-L-cystine.