contains derives from (R)-5-oxo-1,4-tetrahydrothiazine-3-carboxylic acid dehydrated residue S-carboxymethyl-L-cysteine cyclized N-terminal S-carboxymethyl-L-cysteine -18.010564804077148438 -18.020000457763671875 144.011932373046875 144.1699981689453125 artifact A protein modification that effectively cyclizes an S-carboxymethyl-L-cysteine residue to (R)-5-oxo-1,4-tetrahydrothiazine-3-carboxylic acid with the loss of water. 5-oxothiomorpholine-3-carboxylic acid C 5 H 6 N 1 O 2 S 1 PSI-MOD Otc H -2 O -1 MOD:01061 N-term MOD:01872 Pyro-carbamidomethyl S-carbamoylmethylcysteine cyclization (N-terminus) Contrary to the impression given in Unimod entry 26, the cyclization of N-terminal S-carboxymethyl-L-cysteine is not reported in PubMed:1263538. The cyclization would be expected to proceed under strongly acidic conditions [JSG]. (R)-5-oxoperhydro-1,4-thiazine-3-carboxylic acid