Kinetics of interaction of adenosine diphosphate and adenosine triphosphate with adenosine triphosphatase of bovine heart submitochondrial particles

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Abstract
The short preincubation of submitochondrial particles with low concentrations of ADP in the presence of Mg2+ results in a complete loss of their ATPase and inosine triphosphatase activities. Other nucleoside diphosphates (IDP or GDP) do not affect the ATPase activity. The ADP-inhibited ATPase can be activated in a time-dependent manner by treatment of submitochondrial particles with the enzyme converting ADP into ATP (phosphoenolpyruvate plus pyruvate kinase). The activation is a 1st-order reaction with rate constant 0.2 min at 25.degree. C. The rate constant of activation is increased in the presence of ATP up to 2 min and this increase shows saturation kinetics with Km value equal to that for ATPase reaction itself (10-4 M at 25.degree. C at pH 8.0). These experimental results are consistent with the model where 2 alternative pathways of ADP dissociation from the inhibitory site of ATPase exist: one is spontaneous dissociation and the 2nd is ATP-dependent dissociation through the formation of the ternary complex between ADP, the enzyme and ATP. ADP-induced inactivation and ATP-dependent activation of ATPase activity of submitochondrial particles is accompanied by the same directed change of their ability to catalyze the ATP-dependent reverse electron transport from succinate to NAD+. The possible implication of the model suggested is discussed in terms of functional role of the inhibitory high-affinity binding site for ADP in the mitochondrial ATPase.