Direct Measurement of the Reduction Potential of Catalytically Active Cytochrome c Peroxidase Compound I: Voltammetric Detection of a Reversible, Cooperative Two-Electron Transfer Reaction

摘要

Yeast cytochrome c peroxidase (CcP) catalyzes the reduction of hydrogen peroxide to water by cytochrome c(II) in a cycle of processes that have attracted intense and varied interest directed toward developing an understanding of biological electron transfer. As depicted in Scheme 1, the mechanism involves two-electron-oxidation of the Fe(HI) "resting" form of the enzyme to a form known, as CcP compound I (or "ES"), which contains oxyferryl heme (Fe~(IV)=O) and a radical located on the indole ring ofTrp-191. The resting form is regenerated by two sequential one-electron reactions via a form known as CcP compound II, Compound n can exist in at least two forms, [Fe(IV): Trp~0] and [Fe(III): Trp~+] depending upon pH, ionic strength, and the presence of ligands that favor Fe(III). However, only [Fe(lV): Trp~0] has been isolated and characterized in detail.