Single electron reduction of ‘slow’ and ‘fast’ cytochrome-coxidase

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Abstract
Evidence is presented that single electron reduction is sufficient for rapid electron transfer ( k >20 s −1 at pH 8.0 in 0.43 M potassium EDTA) between haem a /Cu A and the binuclear centre in ‘fast’ oxidase, whereas in ‘slow’ oxidase intramolecular electron transfer is slow even when both Cu A and haem a are reduced ( k ⋍2 s −1 ). However, while a single electron can equilibrate rapidly between Cu A , haem a and Cu B in ‘fast’ oxidase, it seems that equilibration with haem a 3 is relatively slow ( k ⋍2 s −1 ). Electron transfer between cytochrome c and Cu A /haem a is similar for both types of enzyme ( k =2.4×10 5 M −1 ·s −1 ).