CHARACTERIZATION OF THE BINDING OF FE(III) TO F(1)ATPASE FROM BOVINE HEART-MITOCHONDRIA

The binding of Fe(III) to F(1)ATPase purified from beef heart mitochon dria has been characterized by chemical analyses and EPR spectroscopy, F(1)ATPase binds 2 mol of Fe(III)/mol of protein selectively in the p resence of saturating concentrations of ATP, In the absence of nucleot ides or in the presence of either saturating ADP or limiting ATP conce ntrations, the enzyme binds 1 equivalent of Fe(III). F(1)ATPase pretre ated with 5'-p-fluorosulfonylbenzoyladenosine, that selectively modifi es the noncatalytic sites, binds only 1 mol of Fe(III)/mol of protein in the presence of either saturating ATP or ADP, Fe(III)-loaded F(1)AT Pase containing either 1 or 2 equivalents of Fe(III) show identical EP R signals at g = 4.3, The signals are not perturbed by the binding of nucleotides to the enzyme while they are altered by phosphate addition , These results indicate that F(1)ATPase contains two distinct Fe(III) -binding sites, which differ from nucleotide-binding sites, and that o ne of these sites is opened up for Fe(III) uptake by conformational ch anges induced by binding of ATP to the loose non-catalytic site.