Applications of B3LYP Method for Enzyme Reactions: O2 Reduction by Cytochrome c Oxidase and Ubiquinol Oxidation by Cytochrome bc1 Complex

摘要

Mechanisms of dioxygen reduction by fully reduced cytochrome c oxidase and ubiquinol oxidation by cytochrome bc1 complex were examined by B3LYP method with the broken-symmetry. In the dioxygen reduction, it was found that protons to form FeOOH and FeOOH2 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 H2O 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 His181 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.