STUDIES ON NUCLEOTIDE SPECIFICITY OF MITOCHONDRIAL INNER MEMBRANE PARTICLES

Submitochondrial particles obtained by treatment with digitonin and by sonication were compared in order to examine the specificity of the phosphate acceptor in oxidative phosphorylation. The digitonin particles behave like intact mitochondria. They have an absolute specificity for ADP in oxidative phosphorylation and for ATP in the Pi-ATP exchange reaction. These reactions, and the 2,4-dinitrophenol-stimulated ATPase, are sensitive to atractyloside. The inhibition of oxidative phosphorylation by atractyloside is competitively reversed by ADP. The finding of Löw, Vallin, and Alm that sonic particles are not absolutely specific for ADP as phosphate acceptor and are insensitive to atractyloside has been confirmed. The atractyloside sensitivity and nucleotide specificity of digitonin particles is not altered by sonication and the properties of sonic particles are not affected by treatment with digitonin. The broad phosphate acceptor specificity of sonic particles is markedly altered by the concentration of divalent cation present in the assay medium. It is concluded that it is unnecessary to invoke the existence of a nucleotide translocase enzyme to account for the differences in phosphate acceptor specificity between the two preparations. The reasons for this conclusion are discussed. © 1969.