title: Modeling the detailed kinetics of mitochondrial cytochrome c oxidase: Catalytic mechanism and nitric oxide inhibition.
abstract: Cytochrome c oxidase (CcO) catalyzes the exothermic reduction of O2to H2O by using electrons from cytochrome c, and hence plays a crucial role in ATP production. Although details on the enzyme structure and redox centers involved in O2reduction have been known, there still remains a considerable ambiguity on its mechanism of action, e.g., the number of sequential electrons donated to O2in each catalytic step, the sites of protonation and proton pumping, and nitric oxide (NO) inhibition mechanism. In this work, we developed a thermodynamically constrained mechanistic mathematical model for the catalytic action of CcO based on available kinetic data. The model considers a minimal number of redox centers on CcO and couples electron transfer and proton pumping driven by proton motive force (PMF), and accounts for the inhibitory effects of NO on the reaction kinetics. The model is able to fit well all the available kinetic data under diverse experimental conditions with a physiologically realistic unique parameter set. The model predictions show that: 1) the apparent Kmof O2varies considerably and increases from fully reduced to fully oxidized cytochrome c depending on pH and the energy state of mitochondria, and 2) the intermediate enzyme states depend on pH and cytochrome c redox fraction and play a central role in coupling mitochondrial respiration to PMF. The developed CcO model can easily be integrated into existing mitochondrial bioenergetics models to understand the role of the enzyme in controlling oxidative phosphorylation in normal and disease conditions.
authors.affiliation: Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin.
authors.forename: Venkat R
authors.initials: VR
authors.lastname: Pannala
authors.affiliation: Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin.
authors.forename: Amadou K S
authors.initials: AK
authors.lastname: Camara
authors.affiliation: Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin; rdash@mcw.edu.|Department of Biomedical Engineering, Medical College of Wisconsin, Milwaukee, Wisconsin; and.
authors.forename: Ranjan K
authors.initials: RK
authors.lastname: Dash
mesh_terms: D002384:Catalysis; D019069:Cell Respiration / Q000502:physiology; D004579:Electron Transport / Q000502:physiology; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008928:Mitochondria / Q000378:metabolism*; D008954:Models, Biological; D009569:Nitric Oxide / Q000378:metabolism*; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation; D010100:Oxygen / Q000378:metabolism; D011522:Protons; D013816:Thermodynamics
chemical_list: D011522:Protons; D009569:Nitric Oxide; D003576:Electron Transport Complex IV; D010100:Oxygen
keywords: half-saturation constant; kinetic modeling; oxygen reduction; proton pumping