ANALYSIS OF THE BINDING OF PARA-CHLOROPHENYL-METHOXYBENZYL-KETOXIME (CPMB-OXIME) TO MITOCHONDRIAL CYTOCHROME-C REDUCTASE

Cytochrome c reductase is inhibited by p-chlorophenyl-methoxybenzyl-ketoxime (CPMB-oxime). CPMB-oxime induces a red-shift of the reduced spectrum of cytochrome b. The inhibitor blocks the oxidation of ubihydroquinone at the Q(P) center of this enzyme in a non-competitive way. The binding stoichiometry equals one inhibitor molecule per Q(p) center. The apparent K(d) in a red-shift assay was 6.9 +/- 0.6-mu-M. All binding characteristics analysed in this study were very similar to those of the E-beta-methoxyacrylate inhibitors, although the chemical structure is different from these inhibitors. This result is interpreted as a support for the inhibitory mechanism based on the model of a 'catalytic switch' proposed recently for the E-beta-methoxyacrylate inhibitors (MOA-inhibitors (Brandt and von Jagow, Eur. J. Biochem. (1991) 195, 163-170).