Analysis of the binding of P ‐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 μM. All binding characteristics analysed in this study were very similar to those of the E‐β‐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‐β‐methoxyacrylate inhibitors (MOA‐inhibitors (Brandt and von Jagow, Eur. J. Biochem. (1991) 195, 163‐170).