FACILITATED INTRAMOLECULAR ELECTRON-TRANSFER IN CYTOCHROME BO-TYPE UBIQUINOL OXIDASE INITIATED UPON REACTION OF THE FULLY REDUCED ENZYME WITH DIOXYGEN

Flow-flash and double-flash studies of the reaction of fully reduced b e-type quinol oxidase with oxygen have revealed that a single turnover of the enzyme proceeds much faster than mammalian cytochrome c oxidas e. Facilitated intramolecular electron transfer in the be-type oxidase with k > 5 x 10(4) s(-1) at pH 7.4 and 20 degrees C is responsible fo r this fast turnover. The kinetics of this reaction indicates that the oxygen reduction does not require electron exchange between quinol ox idase 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 pro vided by the metal centers. A single turnover of the quinol oxidase yi elds a novel spectral species with a Soret maximum at 415 nm correspon ding to a 'pulsed' state of mammalian cytochrome c oxidase.