MG2+-INDUCED ADP-DEPENDENT INHIBITION OF THE ATPASE ACTIVITY OF BEEF-HEART MITOCHONDRIAL COUPLING FACTOR-F1

Incubation of F1 in the presence of Mg2+ results in a pronounced lag in its ATPase activity measured with the ATP-regenerating system. A decrease of the initial rate of ATPase induced by Mg2+ is also observed when free nucleotides were separated from the enzyme by Sephadex gel filtration. No inhibition is observed when F1 treated to remove tightly bound nucleotides was preincubated in the presence of Mg2+. Mg2+-induced inhibition of ATPase activity of nucleotide-depleted F1 can be restored by an addition of low concentrations of ADP. In all cases the inhibited ATPase can be activated by the ADP-removing system /phosphoenol pyruvate + pyruvate kinase/. It is concluded that i/ Mg2+-induced inhibition of the ATPase activity of F1 is due to the formation of an inactive F1. ADP complex; and ii/ unusual inhibition of oligomycin-sensitive ATPase by ADP /Fitin et al., Biochem. Biophys. Res. Communs. 1979, 86, 434/ is directed to F1 component of the complete mitochondrial ATPase system. © 1979.