Facilitated intramolecular electron transfer in cytochrome bo‐type ubiquinol oxidase initiated upon reaction of the fully reduced enzyme with dioxygen

Abstract

Flow-flash and double-flash studies of the reaction of fully reduced bo-type quinol oxidase with oxygen have revealed that a single turnover of the enzyme proceeds much faster than mammalian cytochrome c oxidase. Facilitated intramolecular electron transfer in the bo-type oxidase with k ⪢ 5 × 10⁴ s⁻¹ at pH 7.4 and 20°C is responsible for this fast turnover. The kinetics of this reaction indicates that the oxygen reduction does not require electron exchange between quinol oxidase molecules, each having three metal centers. Thus, a bound quinol in the fully reduced enzyme is suggested to be an electron source for complete reduction of dioxygen into water supplementing electrons provided by the metal centers. A single turnover of the quinol oxidase yields a novel spectral species with a Soret maximum at 415 nm corresponding to a ‘pulsed’ state of mammalian cytochrome c oxidase.