Tightly bound nucleotides affect phosphate binding to mitochondrial F1-ATPase

The interaction of inorganic phosphate with native and nucleotide-depleted F1-ATPase was studied. F1-ATPase depleted of tightly bound nucleotides loses the ability to bind inorganic phosphate. The addition of ATP, ADP, GTP and GDP but not AMP, restores the phosphate binding. The nucleotides affecting the phosphate binding to F1-ATPase are located at the catalytic (exchangeable) site of the enzyme. The phosphate is thought to bind to the same catalytic site where the nucleotide is already bound. It is thought that ADP is the first substrate to bind to F1-ATPase in the ATP synthesis reaction.