title: Dynamics of carbon monoxide recombination to fully reduced cytochrome c oxidase in plant mitochondria after low-temperature flash photolysis.
abstract: Rebinding of CO to reduced cytochrome c oxidase in plant mitochondria has been monitored optically at 590-630 nm after flash photolysis at low temperature from 160 to 200 K. (1) Under 100%-CO saturation, CO rebinding exhibits a four-step mechanism. The thermodynamic parameters of the first phase have been determined; its activation energy, Ea1, is 38.9 kJ.mol-1 and its enthalpy, delta H+/-1, and entropy, delta S+/-1, of activation are respectively 37.5 kJ.mol-1 and -75.8J.mol-1.K-1. (2) When the CO concentration is decreased to 0.2%, rebinding still occurs according to a four-step mechanism. The rate constant of the first phase is CO-concentration-independent. Under non-saturating conditions there is only one CO molecule per occupied site. The rebinding mechanism does not require additional CO molecules to be present in the haem pocket. (3) Dual-wavelength scanning experiments failed to detect optical forms correlated with the resolved phases. (4) Results are discussed with respect to previous work related to CO rebinding to mammalian cytochrome c oxidase and myoglobin.
mesh_terms: D001665:Binding Sites; D002248:Carbon Monoxide / Q000378:metabolism*; D003080:Cold Temperature; D003576:Electron Transport Complex IV / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology*; D008954:Models, Biological; D010084:Oxidation-Reduction; D010782:Photolysis; D010944:Plants / Q000201:enzymology* / Q000648:ultrastructure; D013053:Spectrophotometry; D013816:Thermodynamics
chemical_list: D002248:Carbon Monoxide; D003576:Electron Transport Complex IV