Hepatic cystathionase: Immunochemical and electrophoretic studies of the human and rat forms

Abstract The cystathionases ( l -homoserine hydro-lyase (deaminating), EC 4.2.1.15) of human and rat liver have been purified by starch block and polyacrylamide disc gel electrophoresis. In both cases, purification failed to separate the homolanthionine synthase activity from the cystathionase and homoserine dehydratase activities. Although the enzymes of human and rat liver demonstrate the same activities, they differ in electrophoretic mobility, the human liver cystathionase being a more acidic protein. Injection of the purified preparations, together with the polyacrylamide from their respective disc gel runs, into rabbits has provided monospecific antisera to the two cystathionases. Agar double diffusion analysis demonstrates that the human and rat enzymes share some antigenic determinants. Studies of antibody inhibition provide evidence that in the human liver the three activities of cystathionase, homoserine dehydratase and homolanthionine synthase are on the same protein molecule and at the same active site. This is also the case with rat liver, but rat liver cysteine desulfurase activity, although on the same protein molecule as the other three activities, appears to be at a distinct site more distant from the antigenic site.