Mitochondrial ATP synthase. Interaction of a synthetic 50-amino acid, β-subunit peptide with ATP

A 50-amino acid peptide predicted by chemical modification studies of F₁ and by comparison with adenylate kinase to comprise part of an ATP-binding domain within the β-subunit of mitochondrial ATP synthase has been synthesized and purified. In the numbering system used for bovine heart β, the peptide consists of amino acid residues from aspartate 141 at the N-terminal end of threonine 190 at the carboxyl end. In Tris-Cl buffer, pH 7.4, the peptide undergoes a dramatic reaction with ATP resulting in precipitate formation. Analysis of the precipitate shows it to contain both peptide and ATP. Similar to the ATPase activity of F₁ and the binding of nucleotide to the enzyme, the capacity of ATP to induce precipitation of the peptide is decreased markedly by lowering pH. Interaction of the peptide with the fluorescent ATP analog, TNP-ATP (2'(3')-O-(2,4-6-trinitrophenyl)-adenosine 5'-triphosphate), can be demonstrated in solution at low concentrations. A 7-fold enhancement in fluorescence is observed when 2.5 μM TNP-ATP interacts with 2.5 μM peptide. Divalent cation is neither required for ATP-induced precipitation of the peptide nor for demonstrating interaction between TNP-ATP and peptide, just as Mg²⁺ is not required for nucleotide binding to F₁. These results indicate that the β-subunit peptide studied here comprises at least part of a nucleotide-binding domain within the mitochondrial ATP synthase complex.