pThe paper reports a study of the reaction between phosphoenolpyruvate, ADP and Mgsup2+/sup catalysed by pig liver pyruvate kinase when activated by fructose diphosphate and Ksup+/sup. The experimental results are consistent with two non-sequential mechanisms in which the substrates and products of the reaction are phosphoenolpyruvate, ADP, Mgsup2+/sup, pyruvate and MgATP. Pyruvate release occurs before ADP binding. Two Mgsup2+/sup ions are involved, though the two Mgsup2+/sup-binding sites cannot be occupied simultaneously. An isomerized enzyme complex forms before release of MgATP. Values were determined for the Michaelis constants of the reaction. Apparent MgATP inhibition constants are also given./p
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