Reduction of Coprinus macrorhizus peroxidase by dithionite

Abstract The reduction of Coprinus macrorhizus peroxidase (CMP) by dithionite (Fe(III) → Fe(II)) was studied. CMP reacts with the radical SO 2 − derived from the dithionite ion via saturation kinetics: k abs = a [S 2 O 4 2− ] 1/2 (1 + b [S 2 O 4 2− where a = (1.32 ± 0.06) × 10 3 M −1/2 s −1 and b = 9.16 ± 0.75 −1/2 . It is proposed that SO 2 binds initially to the protein in a non-redox step with an equilibrium constant K 2 = (2.5 ± 0.1 ) × 10 5 M −1 , followed by intramolecular electron transfer, with k = 144 ± 6 s −1 .