Syntheses of S-Substituted L-Homocysteine Derivatives by Cystathionine γ-Lyase of Streptomyces phaeochromogenes

Cystathionine y-lyase from Streptomyces phaeochromogenes catalyzes not only the α,γ-elimination reaction of L-cystathionine, but also the y-replacement reaction of L-homoserine in the presence of thiol compounds. Substrates for the enzyme in the y-replacement reaction were examined. It was found that D-cysteine, L- and D-homocysteine, and 3- and 2-mercaptopropionate served as preferable substrates in the y-replacement reaction. D-Allocystathionine,*¹L- and mesohomolanthionine, S-carboxyethyl-L-homocysteine and S-methylcarboxymethyl-L-homocysteine were enzymatically synthesized from L-homoserine and the corresponding thiol compounds. The thus synthesized S-substituted L-homocysteine derivatives were isolated from large scale reaction mixtures and identified physicochemically.