Filling the Catalytic Site of Cytochrome c Oxidase with Electrons

• Published in: The Journal of biological chemistry 2006-07, Vol.281 (29), p.20003-20010
• Main Authors: Jancura, Daniel, Antalik, Marian, Berka, Vladimir, Palmer, Graham, Fabian, Marian
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M602066200

In the reductive phase of its catalytic cycle, cytochrome c oxidase receives electrons from external electron donors. Two electrons have to be transferred into the catalytic center, composed of heme a3 and CuB, before reaction with oxygen takes place. In addition, this phase of catalysis appears to be involved in proton translocation. Here, we report for the first time the kinetics of electron transfer to both heme a3 and CuB during the transition from the oxidized to the fully reduced state. The state of reduction of both heme a3 and CuB was monitored by a combination of EPR spectroscopy, the rapid freeze procedure, and the stoppedflow method. The kinetics of cytochrome c oxidase reduction by hexaamineruthenium under anaerobic conditions revealed that the rate-limiting step is the initial electron transfer to the catalytic site that proceeds with apparently identical rates to both heme a3 and CuB. After CuB is reduced, electron transfer to oxidized heme a3 is enhanced relative to the rate of entry of the first electron.