Ferrocyanide-peroxidase activity of cytochrome c oxidase

Abstract

Redox interaction of mitochondrial cytochrome c oxidase (COX) with ferrocyanide/ferricyanide couple is greatly accelerated by polycations, such as poly-l-lysine [Musatov et al. (1991) Biological Membranes 8, 229-234]. This has allowed us to study ferrocyanide oxidation by COX at very high redox potentials of the ferrocyanide/ferricyanide couple either following spectrophotometrically ferricyanide accumulation or measuring proton uptake associated with water formation in the reaction. At low [ferrocyanide]/[ferricyanide] ratios (Eh values around 500 mV) and ambient oxygen concentration, the ferrocyanide-oxidase activity of COX becomes negligibly small as compared to the reaction rate observed with pure ferrocyanide. Oxidation of ferrocyanide under these conditions, is greatly stimulated by H2O2 or ethylhydroperoxide indicating peroxidatic reaction involved. The ferrocyanide-peroxidase activity of COX is strictly polylysine-dependent and is inhibited by heme a3 ligands such as KCN and NaN3. Apparently the reaction involves normal electron pathway, i.e. electron donation through CuA and oxidation via heme a3. The peroxidase reaction shows a pH-dependence similar to that of the cytochrome c oxidase activity of COX. When COX is preequilibrated with excess H2O2, addition of ferrocyanide shifts the initial steady-state concentrations of the Ferryl-Oxo and Peroxy compounds towards approximately 2:1 ratio of the two intermediates. It is suggested that in the peroxidase cycleferrocyanide donates electrons to both P and F intermediates with a comparable efficiency. Isolation of a partial redox activity of COX opens a possibility to study separately proton translocation coupled to the peroxidase half-reaction of the COX reaction cycle. Copyright 1998

Mechanism in the reaction of cytochrome c oxidase with organic hydroperoxides: an ESR spin-trapping investigation

“…It has been demonstrated that CcO can undergo a ' peroxidaselike ' reaction at its haem a $ -Cu B binuclear centre, a reaction that has a high K m for H # O # with participation by compound P and compound F intermediates [15,16]. We have employed the ESR spin-trapping technique to investigate the oxidative damage induced in CcO by H # O # [17].…”

An Electron Spin Resonance Spin-trapping Investigation of the Free Radicals Formed by the Reaction of Mitochondrial Cytochromec Oxidase with H2O2

“…The enzyme functions to reduce dioxygen to H 2 O at the active center of heme a 3 -Cu B and couples proton pumping across the mitochondrial inner membrane to provide the driving energy for ATP synthesis (19). It has been reported that a peroxidase-like reaction can occur at the heme a 3 -Cu B center of CcO with a very high K m for H 2 O 2 (20,21). The addition of excess H 2 O 2 can oxidize CcO to yield a peroxy intermediate (or "compound P"), and a one-electron reduction of compound P with either ferrocyanide or cytochrome c yields the ferryl-oxo species (or "compound F").…”

Direct Interaction of Mitochondrial Cytochrome c Oxidase with Thyroid Hormones: Evidence for Two Binding Sites

“…It was shown [32] that the presence of H2O2 enables CcO to operate within a truncated peroxidase cycle bypassing the eu-oxidase phase of the reaction. The reaction of CcO with excess hydrogen peroxide results in the sequential formation of oxoferryl intermediates which are similar in structure to the intermediates FI-607 and FII-580 registered in the oxygen reduction cycle by the rapid kinetic techniques (see reviews [1,2,7,33]).…”

“…As demonstrated in [32], aerobic registration of the peroxidase activity of CcO requires highpotential (Е0  +400 mV) electron donors. Oxidation of such compounds is possible due to the participation of oxoferryl intermediates FI-607 and FII-580 as final acceptors since their one-electron redox transitions are characterized by Е0' around 1 V [35,36].…”