title: Interaction of Zn2+ with the bovine-heart mitochondrial bc1 complex.
abstract: A study is presented of the effect of Zn2+ on the enzymatic properties of the bovine-heart cytochrome-bc1 complex. Micromolar concentrations of Zn2+ reversibly inhibit the cytochrome-c reductase activity of either the cholate-solubilized or liposome-reconstituted complex. Kinetic analysis of the redox reactions of the cytochromes indicate that Zn2+ affects the activity of the complex at the quinol oxidation site. The following have been determined: (a) Zn2+ inhibits the pre-steady-state reduction of cytochrome c1 by duroquinol either in the absence or in the presence of antimycin, (b) it does not inhibit the reduction of b cytochromes in the absence of antimycin or in the presence of myxothiazol, (c) it inhibits cytochrome-b reduction in the presence of antimycin. Furthermore Zn2+ inhibits the antimycin-promoted oxidant-induced extrareduction of b cytochromes. Addition of Zn2+ to reduced bc1 complex causes a red shift in the absorption spectrum of cytochrome b566 and a substantial decrease in the signal intensity of the EPR spectrum of the Fe-S protein. This is interpreted as an interaction of Zn2+ with the 2Fe-2S-cluster region of the Fe-S protein, thus giving rise to inhibition of the reductase activity and of the antimycin-insensitive reduction route of b cytochromes. A Scatchard-plot of 65Zn2+ binding to the native isolated complex gave a straight line from which a value of three binding sites and a single dissociation constant of 3 x 10(-6) M can be calculated, which is practically equal to the concentration causing 50% inhibition of electron flow.
authors.affiliation: Institute of Medical Biochemistry and Chemistry, University of Bari, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Lorusso
authors.forename: T
authors.initials: T
authors.lastname: Cocco
authors.forename: A M
authors.initials: AM
authors.lastname: Sardanelli
authors.forename: M
authors.initials: M
authors.lastname: Minuto
authors.forename: F
authors.initials: F
authors.lastname: Bonomi
authors.forename: S
authors.initials: S
authors.lastname: Papa
mesh_terms: D000818:Animals; D000968:Antimycin A / Q000031:analogs & derivatives / Q000378:metabolism; D002413:Cations, Divalent; D002417:Cattle; D004578:Electron Spin Resonance Spectroscopy; D014450:Electron Transport Complex III / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005292:Ferricyanides / Q000737:chemistry; D006873:Hydroquinones / Q000378:metabolism; D007700:Kinetics; D008929:Mitochondria, Heart / Q000201:enzymology*; D009245:NADH Dehydrogenase / Q000378:metabolism; D010084:Oxidation-Reduction; D011522:Protons; D013057:Spectrum Analysis; D015032:Zinc / Q000378:metabolism*
chemical_list: D002413:Cations, Divalent; D005292:Ferricyanides; D006873:Hydroquinones; D011522:Protons; C032456:antimycin; C007931:hexacyanoferrate III; D000968:Antimycin A; D009245:NADH Dehydrogenase; D014450:Electron Transport Complex III; D015032:Zinc; C016421:duroquinol