Catalytic mechanism of cytochrome c oxidase

Abstract

The structures and kinetic properties of intermediates in the reaction of cytochrome c oxidase with oxygen initiated by CO photolysis were elucidated by resonance Raman scattering studies. These studies led to a postulated model for the reaction involving an initial intermediate with properties similar to oxyhemoglobin, a peroxo intermediate, a ferryl intermediate and a hydroxy intermediate. The influence of initiating the reaction by CO photolysis was tested by comparing the resonance Raman spectra of the reaction product at 10 ms with that generated by directly mixing oxygen with the enzyme in the absence of CO. Different final products were found for these two protocols. It is proposed that in the absence of CO two molecules of O₂ can bind simultaneously at the binuclear site. For single turnover conditions this prevents the reaction from going to completion. However, under physiological conditions where there is a continuous supply of electrons this second molecule of oxygen at the binuclear site places no restrictions on the catalytic mechanism. Instead, it assures an available supply of oxygen to the catalytic site. A model for the reaction under physiological conditions is postulated.