title: Effect of calcium ions on electron transfer between hemes a and a(3) in cytochrome c oxidase.
abstract: Kinetics of the reduction of the hemes in cytochrome c oxidase in the presence of high concentration of ruthenium(III)hexaammine chloride was examined using a stopped-flow spectrophotometer. Upon mixing of the oxidized enzyme with dithionite and Ru(NH(3))(6)(3+), three well-resolved phases were observed: heme a reduction reaching completion within a few milliseconds is followed by two slow phases of heme a(3) reduction. The difference spectrum of heme a(3) reduction in the visible region is characterized by a maximum at ~612 nm, rather than at 603 nm as was believed earlier. It is shown that in the case of bovine heart cytochrome c oxidase containing a special cation-binding site in which reversible binding of calcium ion occurs, heme a(3) reduction is slowed down by low concentrations of Ca(2+). The effect is absent in the case of the bacterial cytochrome oxidase in which the cation-binding site contains a tightly bound Ca(2+) ion. The data corroborate the inhibition of the cytochrome oxidase enzymatic activity by Ca(2+) ions discovered earlier and indicate that the cation affects intramolecular electron transfer.
authors.affiliation: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119991 Moscow, Russia. vygodina@genebee.msu.ru
authors.forename: T V
authors.initials: TV
authors.lastname: Vygodina
authors.forename: A V
authors.initials: AV
authors.lastname: Dyuba
authors.forename: A A
authors.initials: AA
authors.lastname: Konstantinov
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D004579:Electron Transport / Q000187:drug effects; D003576:Electron Transport Complex IV / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006418:Heme / Q000031:analogs & derivatives* / Q000378:metabolism; D007477:Ions / Q000494:pharmacology; D008929:Mitochondria, Heart / Q000201:enzymology / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D007477:Ions; C027728:heme a; D006418:Heme; D003576:Electron Transport Complex IV; D002118:Calcium