COOPERATION AND COMPETITION BETWEEN ADENYLATE KINASE, NUCLEOSIDE DIPHOSPHOKINASE, ELECTRON-TRANSPORT, AND ATP SYNTHASE IN PLANT-MITOCHONDRIA STUDIED BY P-31-NUCLEAR MAGNETIC-RESONANCE

Nucleotide metabolism in potato (Solanum tuberosum) mitochondria was s tudied using P-31-nuclear magnetic resonance spectroscopy and the O-2 electrode. Immediately following the addition of ADP, ATP synthesis ex ceeded the rate of oxidative phosphorylation, fueled by succinate oxid ation, due to mitochondrial adenylate kinase (AK) activity two to four times the maximum activity of ATP synthase. Only when the AK reaction approached equilibrium was oxidative phosphorylation the primary mech anism for net ATP synthesis. A pool of sequestered ATP in mitochondria enabled AK and ATP synthase to convert AMP to ATP in the presence of exogenous inorganic phosphate. During this conversion, AK activity can indirectly influence rates of oxidation of both succinate and NADH vi a changes in mitochondrial ATP. Mitochondrial nucleoside diphosphokina se, in cooperation with ATP synthase, was found to facilitate phosphor ylation of nucleoside diphosphates other than ADP at rates similar to the maximum rate of oxidative phosphorylation. These results demonstra te that plant mitochondria contain all of the machinery necessary to r apidly regenerate nucleoside triphosphates from AMP and nucleoside dip hosphates made during cellular biosynthesis and that AK activity can a ffect both the amount of ADP available to ATP synthase and the level o f ATP regulating electron transport.