title: Complex interactions of carbon monoxide with reduced cytochrome cbb3 oxidase from Pseudomonas stutzeri.
abstract: Cytochrome cbb(3) oxidase, from Pseudomonas stutzeri, contains a total of five hemes, two of which, a b-type heme in the active site and a hexacoordinate c-type heme, can bind CO in the reduced state. By comparing the cbb(3) oxidase complex and the isolated CcoP subunit, which contains the ligand binding bishistidine-coordinated c-type heme, we have deconvoluted the contribution made by each center to CO binding. A combination of rapid mixing and flash photolysis experiments, coupled with computer simulations, reveals the kinetics of the reaction of c-type heme with CO to be complex as a result of the need to displace an endogenous axial ligand, a property shared with nonsymbiotic plant hemoglobins and some heme-based gas sensing domains. The recombination of CO with heme b(3), unlike all other heme-copper oxidases, including mitochondrial cytochrome c oxidase, is independent of ligand concentration. This observation suggests a very differently organized dinuclear center in which CO exchange between Cu(B) and heme b(3) is significantly enhanced, perhaps reflecting an important determinant of substrate affinity.
mesh_terms: D001665:Binding Sites; D002248:Carbon Monoxide / Q000737:chemistry* / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006418:Heme / Q000031:analogs & derivatives* / Q000737:chemistry; D007700:Kinetics; D008024:Ligands; D010084:Oxidation-Reduction; D010782:Photolysis; D021122:Protein Subunits; D011549:Pseudomonas / Q000201:enzymology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013053:Spectrophotometry / Q000379:methods
chemical_list: D008024:Ligands; D021122:Protein Subunits; D011994:Recombinant Proteins; C031690:heme C; D006418:Heme; D002248:Carbon Monoxide; C414443:cbb3 oxidase; D003576:Electron Transport Complex IV