S-aminopropylcysteine and S-aminoethylhomocysteine are oxidized by snake venom L-amino acid oxidase in the presence of catalase with formation of the respective ketoderivatives. Only the ketoderivative of S-aminopropylcysteine cyclizes to give a seven membered ring (ketimine) absorbing at 296 nm. In the absence of catalase both ketoderivatives are oxidatively decarboxylated.
