Effect of pH on CO recombination to cytochrome oxidase in intact mitochondria.
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.
Harmon
H J
HJ
Department of Physics, Oklahoma State University, Stillwater 74078.
Stringer
B K
BK
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
D002248:Carbon Monoxide; D003576:Electron Transport Complex IV