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Non-linear inhibition curves for tight-binding inhibitors of dimeric ubiquinol-cytochrome c oxidoreductases. Evidence for rapid inhibitor mobility.

Bechmann, G; Weiss, H; Rich, PR; (1992) Non-linear inhibition curves for tight-binding inhibitors of dimeric ubiquinol-cytochrome c oxidoreductases. Evidence for rapid inhibitor mobility. Eur J Biochem , 208 (2) pp. 315-325. 10.1111/j.1432-1033.1992.tb17189.x.

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Abstract

Steady-state electron flow through and electron delivery into isolated dimeric bc1 complex (ubiquinol--cytochrome c oxidoreductase) from Neurospora crassa and beef heart mitochondria were studied in the presence of increasing concentrations of antimycin A, funiculosin and/or myxothiazol. Parabolic or linear inhibition curves were obtained, depending upon the different quinols and inhibitors that were used. Linear curves occur when the inhibitor directly affects the rate-determining step. The most reasonable explanation for the parabolic curves is given by a fast intradimeric exchange of the hydrophobic inhibitors antimycin A, funiculosin (rate less than 500 s-1) and of myxothiazol (rate greater than 1 s-1). Using mitochondria from beef heart, the shape of the inhibition curve with antimycin A is parabolic if the quinol--O2 oxidoreductase turns over at about 300 s-1, but hyperbolic if the rate is 5 times less. The hyperbolic titration curve may be the result of both intradimeric and an additional interdimeric redistribution (rate approximately 100 s-1) of inhibitors between enzymes incorporated in a continuous phospholipid membrane. This explanation is supported by experiments with chromatophores obtained from Rhodobacter capsulatus. As recently described [Fernandez-Velasco, J. & Crofts, A. R. (1992) Biophys. J. 2, A153], cytochrome b becomes fully reoxidized within 1 s after a flash at substoichiometric concentrations of antimycin A. This kinetic of the slow reoxidation can be expressed in terms of the intradimeric and interdimeric redistribution with rate constants of about 10 s-1 and 2 x 10(6) M-1 s-1, respectively. It seems that rapid inhibitor redistribution may be a widespread phenomenon for hydrophobic inhibitors of enzymes incorporated in lipid membranes.

Type: Article
Title: Non-linear inhibition curves for tight-binding inhibitors of dimeric ubiquinol-cytochrome c oxidoreductases. Evidence for rapid inhibitor mobility.
Location: England
DOI: 10.1111/j.1432-1033.1992.tb17189.x
Keywords: Animals, Anthraquinones, Antimycin A, Cattle, Cytochrome b Group, Cytochromes c1, Electron Transport, Electron Transport Complex III, Hydroquinones, Kinetics, Macromolecular Substances, Methacrylates, Mitochondria, Heart, Neurospora crassa, Oxidation-Reduction, Substrate Specificity, Thiazoles
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences > Structural and Molecular Biology
URI: http://discovery.ucl.ac.uk/id/eprint/10026611
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