(R)-5-oxo-1,4-tetrahydrothiazine-3-carboxylic acid 144.011932373046875 144.1699981689453125 39.994915008544921875 40.020000457763671875 N-term Otc C 2 O 1 C Pyro-carbamidomethyl artifact A protein modification that effectively converts an L-cysteine residue to (R)-5-oxo-1,4-tetrahydrothiazine-3-carboxylic acid. MOD:00419 C 5 H 6 N 1 O 2 S 1 PSI-MOD S-carbamoylmethylcysteine cyclization (N-terminus) 5-oxothiomorpholine-3-carboxylic acid (R)-5-oxoperhydro-1,4-thiazine-3-carboxylic acid S-carbamoylmethylcysteine cyclization (N-terminus) From DeltaMass: A secondary modification affecting peptides with S-carbamoylmethyl-L-cysteine (CamC) at the N-terminus. These exist in enzymatic digests of proteins that have been S-alkylated with iodoacetamide. Cyclization of N-terminal CamC gives a residue of (R)-5-oxoperhydro-1,4-thiazine-3-carboxylic acid. Peptides in which this has occurred become more hydrophobic, and lose 17 Da from the N-terminal residue. cyclized residue modified L-cysteine residue