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

摘要: Steady-state electron flow through and delivery into isolated dimeric bc1 complex (ubiquinol–cytochrome c oxidoreductase) from Neurospora crassa beef heart mitochondria were studied in the presence of increasing concentrations antimycin A, funiculosin and/or myxothiazol. Parabolic or linear inhibition curves obtained, depending upon different quinols inhibitors that used. Linear occur when inhibitor directly affects rate-determining step. The most reasonable explanation for parabolic is given by a fast intradimeric exchange hydrophobic (rate 1 s−1). Using heart, shape curve with A if quinol – O2 oxidoreductase turns over at about 300 s−1, but hyperbolic rate 5 times less. titration may be result both an additional interdimeric redistribution ∼ 100 s−1) between enzymes incorporated continuous phospholipid membrane. This supported experiments chromatophores obtained Rhodobacter capsulatus. As recently described [Fernandez-Velasco, J. & Crofts, A. R. (1992) Biophys. 2, A153], cytochrome b becomes fully reoxidized within s after flash substoichiometric kinetic slow reoxidation can expressed terms constants 10 s−1 2 × 106 M−1 respectively. It seems rapid widespread phenomenon lipid membranes.