Kinetics of Electron Transfer between Cardiac Cytochrome c1 and c

The kinetics and equilibrium of the electron transfer between isolated cytochrome c1 and cytochrome c and artificial carriers have been studied. The oxidation of ferrocytochrome c1 by ferricyanide showed a rate constant of 3.6 x 104 m-1 s-1 in 50 mm phosphate buffer, pH 7.4, 23°. Under the same condition the rate constant for the reduction of ferricytochrome c1 by ascorbate was found to be 1.2 m-1 s-1. The second order rate constant of the reduction of ferricytochrome c1 by N,N,N',N', tetramethyl-p-phenylenediamine to ferrocytochrome c1 and Wurster's blue was 2 x 104 m-1 s-1 and that of the reverse reaction was 3.9 x 104 m-1 s-1. Wurster's blue could not be further oxidized by either ferricytochrome c1 or ferricytochrome c. The oxidation of ferrocytochrome c1 by ferricytochrome c to ferricytochrome c1 and ferrocytochrome c was not a very fast reaction as generally believed and showed a second order rate constant (k1) of 3.3 x 106 m-1 s-1 at 10° and the reverse reaction showed a rate constant (k-1) of 1.0 x 106 m-1 s-1. These values gave an equilibrium constant (K) of the reaction of 3.3, which was in good agreement with direct spectrophotometric measurements for K. K was independent of the ionic strength and temperature studied, but dependent upon pH. The rate constant, k1, was, however, a function of temperature and ionic strength as well as pH. The reaction rates toward ferricytochrome c were the same whether ferrocytochrome c1 was in the soluble form or structured in a particulate succinate cytochrome c reductase.