Time-resolved Raman detection of .nu.(Fe-O) in an early intermediate in the reduction of oxygen by cytochrome oxidase

Cytochrome oxidase contains four redox-active centers per functional unit: cytochromes a and a3 and the copper atoms, CuA and Cue. Cytochrome c, the physiological substrate of cytochrome oxidase, transfers electrons to the cyt a and CuA sites. These reducing equivalents are transferred to the binuclear cyt a3-CuB center, which binds O2 and reduces it to H20. Although the reaction between O2 and cytochrome oxidase occurs too quickly to be studied by conventional stopped-flow techniques, Gibson and Greenwood' showed that photolysis of the cytochrome a32+-CO complex of the enzyme in the presence of O2 could be used to circumvent this limitation. Babcock et adopted this approach and used time-resolved resonance Raman spectroscopy to study