title: Kinetic studies with cytosol and mitochondrial phosphoenolpyruvate carboxykinases.
abstract: 1. Measurements of Michaelis constants for oxaloacetate in the reaction catalysed by liver phosphoenolpyruvate carboxykinase give values much lower than previously reported. With Mg(2+) as bivalent cation, the Michaelis constant was approx. 2.5x10(-5)m whether the enzyme used was the mitochondrial phosphoenolpyruvate carboxykinase purified from sheep liver or chicken liver or the cytosol enzyme purified from rat liver or sheep liver. 2. When Mn(2+) replaced Mg(2+) in the reaction a lower Michaelis constant of 9x10(-6)m was found, but only with the mitochondrial enzymes. 3. With all enzymes malate at high concentration was a competitive inhibitor with respect to oxaloacetate when Mn(2+) was the added cation. With Mg(2+) the inhibition by malate was competitive with the mitochondrial enzymes and non-competitive with the cytosol enzymes.
mesh_terms: D000818:Animals; D002262:Carboxy-Lyases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002645:Chickens; D002848:Chromatography, DEAE-Cellulose; D003593:Cytoplasm / Q000201:enzymology*; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000201:enzymology*; D008274:Magnesium / Q000378:metabolism; D008293:Malates / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D008930:Mitochondria, Liver / Q000201:enzymology*; D010071:Oxaloacetates / Q000378:metabolism; D051381:Rats; D012756:Sheep
chemical_list: D008293:Malates; D010071:Oxaloacetates; D008345:Manganese; D002262:Carboxy-Lyases; D008274:Magnesium