title: Effects of Zn2+ on the activity and binding of the mitochondrial ATPase inhibitor protein, IF1.
abstract: Zn2+ caused a noninhibitory binding of IF1 to mitochondrial membranes in both rabbit heart SMP and intact rabbit heart mitochondria. This Zn(2+)-induced IF1 binding required the presence of at least trace amounts of MgATP and was essentially independent of pH between 6.2 and 8.2. Addition of Zn2+ after the formation of fully inhibited IF1-ATPase complexes very slowly reversed IF1-mediated ATPase inhibition without causing significant IF1 release from the membranes. When Zn2+ was added during the state 4 energization of ischemic mitochondria in which IF1 was already functionally bound, it slowed somewhat energy-driven ATPase activation. This slowing was probably due to the fairly large depressing effect Zn2+ had upon membrane potential development, but Zn2+ did not decrease the degree of ATPase activation eventually reached at 20 min of state 4 incubation. Zn2+ also preempted normal IF1 release from the membranes, causing what little inhibitor that was released to rebind to the enzyme in noninhibitory IF1-ATPase complexes. The data suggest that IF1 can interact with the ATPase in two ways of through two kinds of sites: (a) a noninhibitory interaction involving a non-inhibitory IF1 conformation and/or an IF1 docking site on the enzyme and (b) an inhibitory interaction involving an inhibitory IF1 conformation and/or a distinct ATPase activity regulatory site. Zn2+ appears to have the dual effect of stabilizing the noninhibitory IF1-ATPase interaction and possibly a noninhibitory IF1 conformation while concomitantly preventing the formation of an inhibitory IF1-ATPase interaction and possibly an inhibitory IF1 conformation, regardless of pH. While the data do not rule out direct effects of Zn2+ on either free IF1 or the free enzyme, they suggest that Zn2+ cannot interact readily with either the inhibitor or the enzyme once functional IF1-ATPase complexes are formed.
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, Ohio 45267-0575.
authors.forename: W
authors.initials: W
authors.lastname: Rouslin
authors.forename: C W
authors.initials: CW
authors.lastname: Broge
authors.forename: B V
authors.initials: BV
authors.lastname: Chernyak
mesh_terms: D000818:Animals; D001665:Binding Sites; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008929:Mitochondria, Heart / Q000187:drug effects* / Q000378:metabolism; D017202:Myocardial Ischemia / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D011487:Protein Conformation; D011506:Proteins / Q000378:metabolism* / Q000494:pharmacology; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors*; D011817:Rabbits; D015032:Zinc / Q000494:pharmacology*; D000097795:ATPase Inhibitory Protein
chemical_list: D011506:Proteins; D006180:Proton-Translocating ATPases; D015032:Zinc; D000097795:ATPase Inhibitory Protein