Kinetic Studies of the Interaction of Ferricytochrome c with Potassium Ferrocyanide by a Chemical Relaxation Technique.

Abstract

A chemical relaxation technique, the temperature jump method, is applied to the study of the kinetics of the interaction of ferricytochrome c with potassium ferrocyanide. The rate constants for both directions of the electron transfer were evaluated. The equilibrium constant derived from these rate constants agreed well with data obtained from spectrophotometric titration and measurement of potentials. The pH-dependence of the rate constant in the forward direction was determined. In general, this curve followed the protolytic titration curve (and E[degree]) but specific effects of considerable magnitude were found in the vicinity (within [plus or minus] 1/4 pH-unit) of pH 7.1, 9.0, (rate increase) and 4.8 (rate decline). The narrowness and symmetry of these extrema indicate that the origin is interaction between conjugate pairs of ionizing groups in the sidechains, possibly carboxyl groups and heme-bound and non-heme-bound imidazole groups.