The site and mechanism of dioxygen reduction in bovine heart cytochrome c oxidase.
J Biol Chem
; 263(27): 13641-54, 1988 Sep 25.
Article
em En
| MEDLINE
| ID: mdl-2843526
ABSTRACT
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.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Oxigênio
/
Complexo IV da Cadeia de Transporte de Elétrons
/
Miocárdio
Limite:
Animals
Idioma:
En
Revista:
J Biol Chem
Ano de publicação:
1988
Tipo de documento:
Article