Sulphur metabolism in Paracoccus denitrificans. Purification, properties and regulation of serine transacetylase, O-acetylserine sulphydrylase and beta-cystathionase.
1. Serine transacetylase, O-acetylserine sulphydrylase and beta-cystathionase were purified from Paracoccus denitrificans strain 8944. 2. Serin transacetylase was purified 150-fold. The enzyme has a pH optimum between 7.5 and 8.0, is specific for L-serine and is inhibited by sulphydryl-group reagents. The apparent Km values for serine and acetyl-CoA are 4.0 - 10(-4) and 1.0 - 10(-4) M, respectively. Serine transacetylase is strongly inhibited by cysteine. 3. O-Acetylserine sulphydrylase was purified 450-fold. The enzymes has a sharp pH optimum at pH 7.5. In addition to catalysing the synthesis of cysteine, O-acetylserine sulphydrylase catalyses the synthesis of selenocysteine from O-acetylserine and selenide. The Km values for sulphide and O-acetylserine are 2.7 - 10(-3) and 1.25 - 10(-3) M, respectively. The enzyme was stimulated by pyridoxal phosphate and was inhibited by cystathionine, homocysteine and methionine. 4. beta-Cystathionase was purified approx. 50-fold. beta-Cystathionase has a pH optimum between pH 9.0 and 9.5, is sensitive to sulphydryl-group reagents, required pyridoxal phosphate for maximum activity and has an apparent Km for cystathionine of 4.2 - 10 (-3) M. beta-Cystathionase also catalyses the release of keto acid from lanthionine, djenkolic acid and cystine. Cysteine, O-acetylserine, homocysteine and glutathione strongly inhibit beta-cystathionase activity and homocysteine and methionine represses enzyme activity. 5. O-Acetylserine lyase was identified in crude extracts of Paracoccus denitrificans. The enzyme is specific  for O-acetyl-L-serine, requires pyridoxal phosphate and is inhibied by KCN and hydroxylamine. The enzyme has a high Km value for O-acetylserine (50--100 mM).
D000105:Acetyl Coenzyme A; D000123:Acetyltransferases / Q000302:isolation & purification / Q000378:metabolism*; D003542:Cystathionine gamma-Lyase / Q000302:isolation & purification / Q000378:metabolism*; D003545:Cysteine / Q000031:analogs & derivatives / Q000096:biosynthesis; D003547:Cysteine Synthase / Q000302:isolation & purification / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008190:Lyases / Q000378:metabolism*; D010231:Paracoccus denitrificans / Q000201:enzymology*; D012643:Selenium; D012694:Serine; D013439:Sulfhydryl Reagents / Q000494:pharmacology
D013439:Sulfhydryl Reagents; D012694:Serine; D000105:Acetyl Coenzyme A; D000123:Acetyltransferases; D003547:Cysteine Synthase; D008190:Lyases; D003542:Cystathionine gamma-Lyase; D012643:Selenium; D003545:Cysteine