The site and mechanism of dioxygen reduction in bovine heart cytochrome c oxidase.
The site and mechanism of dioxygen reduction in cytochrome c oxidase from bovine heart muscle have been investigated. The rate of cytochrome c2+ oxidation by O2 is shown to be affected by several factors: 1) pH, with optima at 5.65 and 6.0, 2) temperature between 0 and 29 degrees C, with E alpha = 13 kcal mol-1, 3) D2O exchange, with a reduction in rate of 50% or more at the pH optima, and 4) the addition of ethylene glycol or glycerol, which significantly lowers the rate. The extremely narrow (delta vCO approximately 4 cm-1) infrared stretch bands at approximately 1964 and approximately 1959 cm-1 for liganded CO are only slightly affected by factors 1-4 or by changes in the oxidation state of metals other than the heme alpha 3 iron. These results indicate a stable, unusually immobile O2 reduction site well-isolated from the external medium, a characteristic expected to be important for oxidase function. Precise stereochemical positioning of hydrogen donors adjacent to O2 liganded to heme alpha 3 iron can be expected in order to achieve the optimization of the time/distance relationships required for enzyme catalysis. These findings support a novel mechanism of O2 reduction via a hydroperoxide intermediate within a reaction pocket that experiences little change in conformation during the hydrogen and electron transfer steps.
Einarsdóttir
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Department of Biochemistry, Colorado State University, Fort Collins 80523.
Choc
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Weldon
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Caughey
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D000818:Animals; D002248:Carbon Monoxide / Q000378:metabolism; D002417:Cattle; D003576:Electron Transport Complex IV / Q000378:metabolism*; D019855:Ethylene Glycol; D005026:Ethylene Glycols / Q000494:pharmacology; D005990:Glycerol / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009206:Myocardium / Q000201:enzymology*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D012997:Solvents; D013055:Spectrophotometry, Infrared; D013696:Temperature; D013816:Thermodynamics
D005026:Ethylene Glycols; D012997:Solvents; D002248:Carbon Monoxide; D003576:Electron Transport Complex IV; D019855:Ethylene Glycol; D005990:Glycerol; D010100:Oxygen