S-Carboxymethylcysteine from the Photolysis of Diazoacyl Trypsin and Chymotrypsin

Photolysis of ethyl diazomalonyl trypsin and of ethyl diazomalonyl chymotrypsin, followed by hydrolysis, yields several products. One of the major products has now been identified as S-carboxymethylcysteine. Since neither trypsin nor chymotrypsin contains an —SH bond, the reaction must involve cleavage of a disulfide bond by the carbene generated on photolysis. The products so far identified from these and similar photochemical experiments illustrate the way in which a carbene, generated at the active site of an enzyme, scans the nearby amino acid residues.