title: Calcium ions inhibit reduction of heme a in bovine cytochrome c oxidase.
abstract: The effect of Ca(2+) on the rate of heme a reduction by dithionite and hexaammineruthenium (RuAm) was studied in the cyanide-complexed bovine cytochrome oxidase (CcO). The rate of heme a reduction is proportional to RuAm concentration below 300 μM with kv of 0.53×10(6) M(-1) s(-1). Ca(2+) inhibits the rate of heme a reduction by dithionite by ∼25%. As the reaction speeds up with increased concentrations of RuAm, the inhibition by Ca(2+) disappears. The inhibition of heme a reduction may contribute to recently described partial inhibition of CcO by Ca(2+) in the enzymatic assays. The inhibitory effect of Ca(2+) on heme a reduction indicates that ET through heme a may be coupled to proton movement in the exit part of the proton channel H.
authors.affiliation: A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119 992, Russia.
authors.forename: Artem V
authors.initials: AV
authors.lastname: Dyuba
authors.affiliation: A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119 992, Russia.
authors.forename: Tatiana
authors.initials: T
authors.lastname: Vygodina
authors.affiliation: A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119 992, Russia.
authors.forename: Natalia
authors.initials: N
authors.lastname: Azarkina
authors.affiliation: A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119 992, Russia. Electronic address: konst1949@gmail.com.
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Konstantinov
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002417:Cattle; D004227:Dithionite / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004579:Electron Transport / Q000187:drug effects; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006418:Heme / Q000031:analogs & derivatives* / Q000378:metabolism; D007700:Kinetics; D017975:Ruthenium Compounds / Q000494:pharmacology
chemical_list: D017975:Ruthenium Compounds; D004227:Dithionite; C027728:heme a; C031584:hexammineruthenium; D006418:Heme; D003576:Electron Transport Complex IV; D002118:Calcium
keywords: Calcium; Cytochrome oxidase; Electron transfer; H proton channel; Respiratory chain