Xarboxymethylcysteine from the Photolysis

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 identzed 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.