title: Cysteine and homocysteine synthesis in Saccharomycopsis lipolytica; identification and characterization of two cysteine synthases.
abstract: In Saccharomycopsis (Candida) lipolytica direct cysteine synthesis is mediated by two different, simultaneously acting cysteine synthases: a low molecular mass (74,000 daltons) monofunctional enzyme (Km for O-acetyl-l-serine 23.5 mm) and a high molecular mass (220,000 daltons) bifunctional cysteine-homocysteine synthase (Km for O-acetyl-l-serine 55.0 mm). The latter enzyme is also involved in direct homocysteine synthesis from O-acetyl-l-homoserine (Km 11.9 mm). Evidence is presented that a fraction of homocysteine can be synthesized from cysteine via cystathionine. Our previous results (Morzycka & Paszewski, FEBS Lett., 1979, 101, 97-100; Mol. Gen. Genet., 1979, 174, 33-38) together with the data presented here strongly suggest that both S., lipolytica synthases are under control of the same regulatory system, together with the other enzymes of sulphur metabolism: ATP-sulphurylase and aryl-sulphatase. gamma-Cystathionase, an enzyme involved in cysteine synthesis from homocysteine, is controlled exclusively by cysteine.
mesh_terms: D001203:Ascomycota / Q000201:enzymology*; D019757:Carbon-Oxygen Lyases; D003540:Cystathionine / Q000378:metabolism; D003542:Cystathionine gamma-Lyase / Q000378:metabolism; D003545:Cysteine / Q000096:biosynthesis*; D003547:Cysteine Synthase / Q000378:metabolism*; D006710:Homocysteine / Q000096:biosynthesis*; D008190:Lyases / Q000378:metabolism*; D009097:Multienzyme Complexes; D009154:Mutation; D011732:Pyridoxal Phosphate / Q000494:pharmacology; D029701:Saccharomyces cerevisiae Proteins; D012442:Saccharomycopsis / Q000201:enzymology* / Q000235:genetics; D013379:Substrate Specificity
chemical_list: D009097:Multienzyme Complexes; D029701:Saccharomyces cerevisiae Proteins; D006710:Homocysteine; D003540:Cystathionine; D011732:Pyridoxal Phosphate; D003547:Cysteine Synthase; C103381:MET17 protein, S cerevisiae; C018725:O-acetylhomoserine (thiol)-lyase; D008190:Lyases; D019757:Carbon-Oxygen Lyases; D003542:Cystathionine gamma-Lyase; D003545:Cysteine