Binding Properties of 9K Protein to F1-ATPase: A Counterpart Ligand to the ATPase Inhibitor

• Published in: Journal of biochemistry (Tokyo) Vol. 102; no. 4; pp. 685 - 692
• Main Authors: HASHIMOTO, Tadao, YOSHIDA, Yukuo, TAGAWA, Kunio
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01.10.1987
• Subjects: Analytical, structural and metabolic biochemistry; Binding, Competitive; Biological and medical sciences; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; Hydrolases; Ligands; Proton-Translocating ATPases - antagonists & inhibitors; Proton-Translocating ATPases - metabolism; Yeasts - enzymology; F1-ATPase; Ligand binding; Yeast; Enzyme; Enzyme inhibitor; Regulatory subunit; Inactivation; Proteins; Mitochondria; Magnesium Ions; Molecular complex; ATP; Catalyst activity; Comparative study
• ISSN: 0021-924X; 1756-2651
• DOI: 10.1093/oxfordjournals.jbchem.a122106

A regulatory subunit of yeast mitochondrial ATP synthase, 9K protein, formed an equimolar complex with F1 ATPase in the presence of ATP and Mg2+, indicating that the binding of the protein to the enzyme took place in a similar manner to that of ATPase inhibitor. The ATP-hydrolyzing activity of F1 ATPase decreased 40% on binding of the 9K protein, and the remaining activity was resistant to external ATPase inhibitor. The apparent dissociation constant of the F1-ATPase-9K complex was determined by gel permeation chromatography to be 3.7 × 10−6M, which was in the same order of magnitude as that of enzyme-ATPase inhibitor complex (4.2 × 10−6 M). When added simultaneously the binding of the inhibitor and 9K protein to F1-ATPase were competitive and the sum of their bindings did not exceed 1 mol per mol of enzyme. However, the binding of each protein ligand to F1-ATPase took more than 1 min for completion, and when one of these two proteins was added 10 min after the other, it did not replace the other. These observations strongly suggest that membrane-bound F1-ATPase always binds to either the 9K protein or ATPase inhibitor in intact mitochondria and that the complexes with the two ligands are active and inactive counterparts, respectively.