title: Effect of pH on CO recombination to cytochrome oxidase in intact mitochondria.
abstract: The rate of recombination of CO with fully reduced cytochrome oxidase in intact beef heart mitochondria was measured after flash photolysis at temperatures between 180 and 230K. At pH 7.4 a single Arrhenius slope corresponds to an apparent energy of activation (Ea) of 10.5 kcal/mol; the rate constants in 100% CO are twice those in the presence of 1% CO. At pH 5.5 with 100% CO, Ea's of 11.3 and 7.1 kcal/mol are observed above and below 210K, respectively, while Ea's of 7.4 and 11.1 kcal/mol are observed with 1% CO above and below 210K. At pH 9.0 Ea's of 9.2 (above 200K), 12.5 (190-200K), and 2.3 (below 190K) kcal/mol are observed with 1% CO; Ea's of 9.4, 13.4, and 2.4 kcal/mol are observed in the same temperature ranges with 100% CO present. The findings support a model with up to 4 energy barriers separating the heme region from the bulk medium with intermediate regions that can hold 1 or 2 CO, depending on pH.
authors.affiliation: Department of Physics, Oklahoma State University, Stillwater 74078.
authors.forename: H J
authors.initials: HJ
authors.lastname: Harmon
authors.forename: B K
authors.initials: BK
authors.lastname: Stringer
mesh_terms: D000818:Animals; D001692:Biological Transport; D002248:Carbon Monoxide / Q000378:metabolism*; D002417:Cattle; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008929:Mitochondria, Heart / Q000201:enzymology*; D010782:Photolysis; D013816:Thermodynamics
chemical_list: D002248:Carbon Monoxide; D003576:Electron Transport Complex IV