Applications of B3LYP Method for Enzyme Reactions: O_2 Reduction by Cytochrome c Oxidase and Ubiquinol Oxidation by Cytochrome bc_1 Complex

摘要

Mechanisms of dioxygen reduction by fully reduced cytochrome c oxidase and ubiquinol oxidation by cytochrome bc_1 complex were examined by B3LYP method with the broken-symmetry. In the dioxygen reduction, it was found that protons to form FeOOH and FeOOH_2 are provided through the K-channel, and at the same time an electron transfer occurs to FeOO from the reduced Cu(I) through the prophyrin ring. The mechanism is proposed for first H_2O formation. In the ubiquinol oxidation, it was found that the ubiquinol can be docked in both His181 of Rieske iron-sulfur protein and Glu272 of cytochrome b protein. Two protons and one electron transfer simultaneously from ubiquinol to Hisl81 and Glu272 to yield one-electron reduced [2Fe-2S] cluster from the oxidized state. The concerted proton and electron transfers were found in both enzymes.