Formation and decay of cytochrome c peroxidase compound ES during aerobic redution with dithionite

Abstract

Stopped-flow and rapid scanning studies have clearly demonstrated that mixing of an oxygen-saturated solution of yeast cytochrome c peroxidase with sodium dithionite yields compound ES, indicating generation of H 2O 2. The formation of compound ES was most pronounced when [Na 2S 2O 4/[O 2] ≈ 1, and it reverted to the ferric form while standing. Even in the presence of an excess of dithionite ([Na 2S 2O 4]/[O 2] = 3.4) compound ES was formed immediately, but was soon replaced by the ferric form, followed by its final reduction to the ferrous state. The apparent first order rate constant for the decay of compound ES to the ferric form increased linearly with the square root of the dithionite concentration, thus involvement of SO − 2 in that process being suggested.