Pyruvate carboxylase from Penicillium camemberti 5. Regulation of the enzyme activity by the ratio of ATP and ADP

Abstract

1. 1. Pyruvate carboxylase from Penicillium camemberti was studied on a partially purified preparation using kinetic methods. 2. 2. The equilibrium concentrations of all ions in the dissociation equilibrium between magnesium, ATP, and ADP were calculated. The enzyme activity was determined as a function of the actual concentrations of substiates and inhibitors. 3. 3. The apparent Michaelis constant for MgATP 2− was 0·24 m M at pH 8·0 and under a defined concentration of all other ions. Magnesium did not influence the K m value of MgATPsu2− but diminished the V max. MgADP − is a competitive inhibitor against MgATP 2− ( K i = 0.17 m M). 4. 4. The dependence of the pyruvate carboxylase activity on the energy charge of the adenylate pool, as calculated from the values of K i for MgADP − and K m for MgATP 2−, coincides with the experimentally derived results.