Abstract
Beef heart mitochondrial ATPase (F1) exhibited a single binding site for Pi. The interaction with Pi was reversible, partially dependent on the presence of divalent metal ions, and characterized by a dissociation constant at pH 7.5 of 80 micronM. A variety of substances known to influence oxidative phosphorylation or the activity of the soluble ATPase (F1) also influenced Pi binding by the enzyme. Thus aurovertin, an inhibitor of oxidative phosphorylation, which was bound tightly by F1 and inhibited ATPase activity, enhanced Pi binding via a 4-fold increase in the affinity of the enzyme for Pi (KD = 20 micronM) but did not alter binding stoichiometry. Anions such as SO4(2-), SO3(2-), chromate, and 2,4-dinitrophenolate, which stimulated ATPase activity of F1, also enhanced Pi binding. Inhibitors of ATPase activity such as nickel/bathophenanthroline and the protein ATPase inhibitor of Pullman and Monroy (Pullman, M. E., and Monroy, G. C. (1963) J. Biol. Chem. 238, 3762-3769) inhibited Pi binding. The adenine nucleotides ADP, ATP, and the ATP analog adenylyl imidodiphosphate as well as the Pi analog arsenate, also inhibited Pi binding. The observations suggest that the Pi binding site was located in or near an adenine nucleotide binding site on the molecule.
Highlights
The purpose of this paper is to describe specific, reversible interactions of F, with P, and to show that the enzyme exhibits a single binding site for this ligand
Two independent methods of analysis revealed that incubation of F, with 32Pi resulted in binding of Pi by the enzyme
Pi binding was slightly underestimated by the latter procedure
Summary
[‘4ClEDTA, and a*P1, enzyme grade, were purchased from ICN Corp., Isotope and Nuclear Division. :rzPL was used without further purification. [‘4ClEDTA, and a*P1, enzyme grade, were purchased from ICN Corp., Isotope and Nuclear Division. Filtration membranes (XM-50) for the pressure dialysis cell were obtained from Amicon. G-50 fine was purchased from Pharmacia, Piscataway, N. J. ATP and ADP were obtained from Sigma. All other chemicals were of reagent grade quality. Solutions of cobalt and manganese were prepared fresh from the dry salt for each experiment.
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