title: Single-electron photoreduction of the P(M) intermediate of cytochrome c oxidase.
abstract: The P(M)-->F transition of the catalytic cycle of cytochrome c oxidase from bovine heart was investigated using single-electron photoreduction and monitoring the subsequent events using spectroscopic and electometric techniques. The P(M) state of the oxidase was generated by exposing the oxidized enzyme to CO plus O2. Photoreduction results in rapid electron transfer from heme a to oxoferryl heme a3 with a time constant of about 0.3 ms, as indicated by transients at 605 nm and 580 nm. This rate is approximately 5-fold more rapid than the rate of electron transfer from heme a to heme a3 in the F-->O transition, but is significantly slower than formation of the F state from the P(R) intermediate in the reaction of the fully reduced enzyme with O2 to form state F (70-90 micros). The approximately 0.3 ms P(M)-->F transition is coincident with a rapid photonic phase of transmembrane voltage generation, but a significant part of the voltage associated with the P(M)-->F transition is generated much later, with a time constant of 1.3 ms. In addition, the P(M)-->F transition of the R. sphaeroides oxidase was also measured and also was shown to have two phases of electrogenic proton transfer, with tau values of 0.18 and 0.85 ms.
authors.affiliation: A N Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119 992, Russia.
authors.forename: Sergey A
authors.initials: SA
authors.lastname: Siletsky
authors.forename: Dan
authors.initials: D
authors.lastname: Han
authors.forename: Sue
authors.initials: S
authors.lastname: Brand
authors.forename: Joel E
authors.initials: JE
authors.lastname: Morgan
authors.forename: Marian
authors.initials: M
authors.lastname: Fabian
authors.forename: Lois
authors.initials: L
authors.lastname: Geren
authors.forename: Francis
authors.initials: F
authors.lastname: Millett
authors.forename: Bill
authors.initials: B
authors.lastname: Durham
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Konstantinov
authors.forename: Robert B
authors.initials: RB
authors.lastname: Gennis
mesh_terms: D000818:Animals; D001665:Binding Sites; D002248:Carbon Monoxide / Q000378:metabolism; D002417:Cattle; D003300:Copper / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000378:metabolism*; D004583:Electrons; D006418:Heme / Q000378:metabolism; D007700:Kinetics; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010777:Photochemistry; D011522:Protons; D012242:Rhodobacter sphaeroides / Q000201:enzymology*
chemical_list: D011522:Protons; D006418:Heme; D003300:Copper; D002248:Carbon Monoxide; D003576:Electron Transport Complex IV; D010100:Oxygen