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Kinetic studies with cytosol and mitochondrial phosphoenolpyruvate carboxykinases

1970; Portland Press; Volume: 120; Issue: 4 Linguagem: Inglês

10.1042/bj1200809

0306-3283

F J Ballard,

ATP Synthase and ATPases Research

1. Measurements of Michaelis constants for oxaloacetate in the reaction catalysed by liver phosphoenolpyruvate carboxykinase give values much lower than previously reported. With Mg2+ as bivalent cation, the Michaelis constant was approx. 2.5×10−5m 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 Mn2+ replaced Mg2+ in the reaction a lower Michaelis constant of 9×10−6m 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 Mn2+ was the added cation. With Mg2+ the inhibition by malate was competitive with the mitochondrial enzymes and non-competitive with the cytosol enzymes.