[en] The reduction of acetylated, fully succinylated and dicarboxymethyl horse cytochromes c by the radicals CH₃CHOH, CO₂, O₂, and e^-/sub aq/, and the oxidation of the reduced cytochrome c derivatives by Fe(CN)₆^3- were studied using the pulse radiolysis technique. Many of the reactions were also examined as a function of ionic strength. By obtaining rate constants for the reactions of differently charged small molecules redox agents with the differently charged cytochrome c derivatives at both zero ionic strength and infinite ionic strength, electrostatic and conformational contributions to the electron transfer mechanism were effectively partitioned from each other in some cases. In regard to cycochrome c electron transfer mechanism, the results, especially those for which conformational influences predominate, are supportive of the electron being transferred in the heme edge region