Do copper ions influence the reduction of ferricytochrome [formula omitted] by O −2?

Abstract

Recently, it was suggested that the measured rate of reduction of ferricyto chrome C by O − 2 below pH 8, was too high in the presence of high concentrations of formate (Koppenol, W.H., Van Buuren, K.J.H., Butler J. and Braams, R. (1976) Biochim. Biophys. Acta 449, 157–168). The high values were attributed to the presence of impurities of copper, which compete for O − 2. This assumption is consistent with either a decrease in the reduction yield of ferricytochrome C in the presence of copper, or with a very fast reaction of Cu(I) with ferricytochrome C. It was previously shown by us and by others that the reduction yield of ferricytochrome C by O − 2 is 100%. We measured the rate of reduction of ferricytochrome C by Cu(I), and found that this reaction is slow: k = (1.5±0.5) · 10 3 M −1) · s −1 . Therefore, our results rule out the possibility that below pH 8 copper impurities affect the measured rate constant of the reduction of ferricytochrome C by O − 2.