Reductions by ferrocytochrome c peroxidase 4. Kinetics of yeast cytochrome c reduction at high buffer phosphate concentration

Phosphate mediated adsorption and electron transfer of cytochrome c. A time-resolved SERR spectroelectrochemical study

The study of proteins immobilized on biomimetic or biocompatible electrodes represents an active field of research as it pursues both fundamental and technological interests. In this context, adsorption and redox properties of cytochrome c (Cyt) on different electrode surfaces have been extensively reported, although in some cases with contradictory results. Here we report a SERR spectroelectrochemical study of the adsorption and electron transfer behaviour of the basic protein Cyt on electrodes coated with amino-terminated monolayers. The obtained results show that inorganic phosphate (Pi) and ATP anions are able to mediate high affinity binding of the protein with preservation of the native structure and rendering an average orientation that guarantees efficient pathways for direct electron transfer. These findings aid the design of Cyt-based bioelectronic devices and understanding the modulation by Pi and ATP of physiological functions of Cyt.

Yeast cytochrome c peroxidase: mechanistic studies via protein engineering

Cytochrome c peroxidase (CcP) is a yeast mitochondrial enzyme that catalyzes the reduction of hydrogen peroxide to water by ferrocytochrome c. It was the first heme enzyme to have its crystallographic structure determined and, as a consequence, has played a pivotal role in developing ideas about structural control of heme protein reactivity. Genetic engineering of the active site of CcP, along with structural, spectroscopic, and kinetic characterization of the mutant proteins has provided considerable insight into the mechanism of hydrogen peroxide activation, oxygen-oxygen bond cleavage, and formation of the higher-oxidation state intermediates in heme enzymes. The catalytic mechanism involves complex formation between cytochrome c and CcP. The cytochrome c/CcP system has been very useful in elucidating the complexities of long-range electron transfer in biological systems, including protein-protein recognition, complex formation, and intracomplex electron transfer processes.

Cytochrome c binding to Apaf-1: the effects of dATP and ionic strength

In the apoptosis pathway in mammals, cytochrome c and dATP are critical cofactors in the activation of caspase 9 by Apaf-1. Until now, the detailed sequence of events in which these cofactors interact has been unclear. Here, we show through fluorescence polarization experiments that cytochrome c can bind to Apaf-1 in the absence of dATP; when dATP is added to the cytochrome c.Apaf-1 complex, further assembly occurs to produce the apoptosome. These findings, along with the discovery that the exposed heme edge of cytochrome c is involved in the cytochrome c.Apaf-1 interaction, are confirmed through enhanced chemiluminescence visualization of native PAGE gels and through acrylamide fluorescence quenching experiments. We also report here that the cytochrome c.Apaf-1 interaction depends highly on ionic strength, indicating that there is a strong electrostatic interaction between the two proteins.

Reductions by ferrocytochrome c peroxidase: 5. Kinetics of ferricyanide reduction

The kinetics of reduction of ferricyanide by yeast ferrocytochrome c peroxidase (CPPII) were investigated as a function of ionic strength in phosphate buffers at pH 7.0 and 25 ± 1 °C. The observed bimolecular rate constant (k12) is 8.4 × 104 M−1s−1in 0.1 M phosphate. The dependence of the reaction rate on ionic strength indicates a change of −9 on the protein at pH 7.0, which is in good agreement with the total charge of −11 estimated for CCPIIfrom its amino acid content. Substituting k12at infinite ionic strength [Formula: see text] into the Marcus cross relation yields an electron self-exchange rate constant [Formula: see text] for the FeIII/FeIIcouple of CCP of 7.2 × 10−5 M−1s−1. This value is over four orders of magnitude higher than that calculated for the FeIV/FeIIIcouple of CCP from literature data for cross-reactions with ferrocyanide at pH 7.0. Possible reasons for the large difference in the two CCP [Formula: see text] values are discussed. Literature data also allowed [Formula: see text] values for various other heme proteins to be determined from their cross-reactions with ferricyanide. The calculated rate constants vary by eight orders of magnitude, and the variation of [Formula: see text] with protein structure suggests that the redox reactivity of ferrous heme proteins towards ferricyanide is dependent on the spin state and coordination of iron, as well as on the accessibility of the heme. Keywords: cytochrome c peroxidase, ferricyanide, Marcus cross relation, electron self-exchange.