Collect. Czech. Chem. Commun. 1991, 56, 1552-1559

Kinetics and mechanism of the cytochrome c – sulfite reaction

Joaquin F. Perez-Benito and Conchita Arias

Departamento de Quimica Fisica, Facultad de Quimica, Universidad de Barcelona, 08028 Barcelona, Spain


The reaction between the oxidized form of horse-heart cytochrome c and sodium sulfite in aqueous solution has been studied in the pH range 6.5 – 8.2. The reaction is first order in both oxidant and reductant, is accelerated by an increase in pH and is slowed down by addition of potassium chloride. An increase in pH results in an increase in the apparent activation energy (66-77kJ . mol-1). A mechanism in which both HSO3- and SO32- act as reducing agents is proposed, the activation energies corresponding to the cyt c-HSO3- and cyt c-SO32- reactions being 63 ± 4 and 79 ± 2 kJ mol-1, respectively.