Syntheses of s-substituted l-homocysteine derivatives by cystathionine γ-lyase of streptomyces phaeochromogenes

Cystathionine γ-lyase from Streptomyces phaeochromogenes catalyzes not only the a, y-elimination reaction of L-cystathionine, but also the γ-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, ^land D-homocysteine, and 3-and 2-mercaptopropionate served as preferable substrates in the y-replacement reaction, d-Allocystathionine, ^*1 L-and meso-homolanthionine, 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.