Role Of The Mitochondrial Adenylate Kinase And Bivalent Cations In The Regulation Of Adenine Nucleotide Metabolism

Abstract

Introduction The purpose of this study is to characterize further, the manner in which the mitochondrial enzyme, adenylate kinase and the mitochondrial bivalent cation transport interact functionally with the oxidative phosphorylation machinery of the cell in the regulation of adenine nucleotide metabolism. The work has been carried out in two parts. PART ONE Various parameters of the mitochondrial adenylate kinase have been investigated, with an aim of understanding further how its interaction with intra - and extramitochondrial adenine nucleotides together with the process of oxidative phosphorylation may participate in regulating the metabolic interplay between the cytosol and the mitochondria, with special emphasis on adenine nucleotide metabolism. Most of the work has been carried out with intact rat liver mitochondria, which allowed a study of the functional relationship between the adenylate kinase (located in the mitochondrial outer compartment) and the oxidative phosphorylation machinery of the mitochondria on one hand, and that between adenylate kinase and the extramitochondrial environment. The results show that both the direction and velocity of the adenylate kinase reaction are influenced by the relative concentrations of the adenine nucleotides in its environment. This in turn has a strong influence on the rate of oxidative phosphorylation. With a high concentration of ATP and AMP in the extramitochondrial environment the forward reaction of the adenylate kinase is strongly stimulated. On the other hand, with a high concentration of ADP, the reverse reaction is strongly stimulated. In the presence of a respiratory substrate and inorganic phosphate, AMP and ADP stimulate both the adenylate kinase reaction and oxidative phosphorylation while ATP has no effect on either of the reactions. With AMP, oxidative phosphorylation is stimulated, with a respiratory control ratio similar to that for ADP. This effect is due to the presence of small amounts of ATP in the mitochondrial outer compartment which react with AMP forming ADP under the catalysis of the adenylate kinase, with the ADP so formed initiating oxidative phosphorylation. A comparison of the amount of ATP formed, with AHP as the substrate