A Study of the Mechanism of Electron Transfer in Cytochrome c

Abstract

Abstract Cytochrome c is swiftly and quantitatively reduced by chromous ion. In the course of the reduction chromium is bound to the protein. At pH 4.78 and 7.0 the ratio of chromium to cytochrome c is approximately 0.5 mole per mole. When phosphate is present during the reduction, the ratio increases to approximately unity, and 1 mole of phosphate is also bound. The chromium-ferrocytochrome c complex can be reoxidized with ferricyanide with little loss of chromium and can be reduced again with dithionite. However, if chromous ion is used to reduce ferricytochrome c-chromium, only partial reduction occurs. The cytochrome c-chromium-phosphate complex is active with cytochrome oxidase and with the cytochrome c reductase of a bovine heart submitochondrial preparation. In the latter system, however, rates are markedly lower. The cytochrome c-chromium-phosphate complex has been digested with pepsin, and a crude fraction has been isolated which still contains iron, chromium, and phosphate.