The Reduction of Ferricytochrome c Studied by Pulse Radiolysis

Abstract The formation of ferrocytochrome c upon pulse radiolysis of aqueous solutions of ferricytochrome c has been studied by following spectral shifts at 550 nm and 700 nm. The reaction between ferricytochrome c and hydrated electrons was studied by following the decay of hydrated electrons as well as the ferrocytochrome c formation. The two processes proceed with the same rate which indicate diffusion‐controlled processes with a second order rate constant of 1.1 × 1011 M−1 sec−1. The reaction between ferricytochrome c and H atoms was studied in a system containing H atoms only and found to be a second order reaction with a rate constant of 1.5 × 1010 M−1 sec−1. The formation of ferrocytochrome c by reaction between ferricytochrome c and OH radicals proceed by a first step with a second order rate constant of 1.4 × 1010 M−1 sec−1 during which OH radicals react with the protein part of ferricytochrome c forming an organic radical. Some of these radicals then undergo intramolecular reduction with a rate constant of 3.1 × 103 sec−1.