The role of the ADP-ATP exchange enzyme in oxidative phosphorylation

Abstract

1. A nucleoside diphosphate kinase (EC 2.7.4.6) has been isolated from liver mitochondria that is rather specific for ATP as phosphate donor. It catalyses an ADP-ATP exchange reaction. 2. The isolated enzyme is inhibited by ADP in concentrations higher than 1 mM. The reaction is stimulated by both ferri- and ferrocytochrome c, but the inhibition by high ADP concentrations is not relieved. 3. The isolated enzyme is insensitive to 2,4-dinitrophenol and oligomycin. It appears to become sensitive to 2,4-dinitrophenol but not to oligomycin on addition of freshly prepared digitonin particles. The inhibition is due to the formation of ADP, catalysed by the adenosine triphosphatase in the digitonin particles. 4. The oligomycin-sensitive ADP-ATP exchange activity in the mitochondria is not affected by extraction of the nucleoside diphosphate kinase. 5. The isolated enzyme has no effect either on the P/O ratio or on the ATP-driven nicotinamide nucleotide transhydrogenase of submitochondrial particles. 6. A role of this enzyme in oxidative phosphorylation seems improbable.