Insight into the active site of Streptomyces cystathionine γ-lyase based on the results of studies on its substrate specificity

The results of studies on the substrate specificities of elimination and replacement reactions allowed insight into the active and regulatory sites of Streptomyces phaeochromogenes cystathionine γ-lyase l-cystathionine cysteine-lyase (deaminating), EC 4.4.1.1). The enzyme has an active site and a regulatory site. The active site consists of two subsites; one recognizes the l-forms of animo acids (l-homoserine and l-moieties of cystathionine isomers) and the other shows affinity for thiol compounds with a carboxyl group. The regulatory site is specific for l-cysteine and has no affinity for ordinary thiol compounds, such as 3-mercaptopropionate and thioglycolate.