Cytochrome c oxidized

RL Cutler, AM Davies, S Creighton, A Warshel, GR Moore, M Smith, AG Mauk. Role of arginine-38 in regulation of the cytochrome c oxidation-reduction equilibrium. Biochemistry 28 3188-3197, 1989. 

FIGURE 21.9 Typical visible absorption spectra of cytochromes, (a) Cytochrome c, reduced spectrum (b) cytochrome c, oxidized spectrum (c) the difference spectrum (a) minus (b) (d) beef heart mitochondrial particles room temperature difference (reduced minus oxidized) spectrum (e) beef heart submitochondrial particles same as (d) but at 77 K. a- and /3- bauds are labeled, and in (d) and (e) the bauds for cytochromes a, h and c are indicated. 

Skulachev [117] proposed that the released cytochrome c oxidizes superoxide and, by this, exhibits an antioxidant function. This proposal was supported by recent experimental findings by Atlante et al. [118], who suggested that cytochrome c released from mitochondria by oxygen species protected mitochondria through a feedback-like process oxidizing superoxide. The most important physiological inhibitor of apoptosis is multifunctional protein Bcl-2,... 

To obtain reduced cytochrome c, oxidative form of cytochrome c is reduced by ascorbic acid described as follows. 

The non-congruence of the values for interaction of the mutants with cytochrome c oxidase with the K , values calculated from the steady-state kinetic analysis included in this study suggests that the rate of cytochrome c oxidation by the oxidase is not limited by the rate of product dissociation. 

Figure 19. Relative reactivities of oxoferryl Mbs toward small substrate and cytochrome c oxidations.

Diederich et al.11921 reported the divergent synthesis of dendrimers possessing porphyrin cores with the aim of modeling redox potentials of electroactive chromophores via environmental polarity modification. The dendrimers thus can be considered as electron-transfer protein mimics for such proteins as cytochrome c oxidation potentials for cytochrome c in aqueous solution are known to be 300-400 mV more positive than those reported for similarly ligated heme mimics lacking hydrophobic peptide encapsulation J193a ... 

The pH dependence of cytochrome c oxidation-reduction reactions and the studies of modified cytochrome c thus demonstrate that the coordination environment of the iron and the conformation of the protein are relatively labile and strongly influence the reactivity of the metallo-protein toward oxidation and reduction. The effects seen may originate chiefly from alterations in the thermodynamic barriers to electron transfer, but the conformation changes are expected to affect the intrinsic barriers also. One such conformation change is the opening of the heme crevice referred to above. The anation and Cr(II) reduction studies provide an estimate of 60 sec 1 for this process in Hh(III) at 25°C (59). To date, no evidence has been found for a rapid heme-crevice opening step in ferrocytochrome c. 

Figure 2. Electron transfer kinetics of cytochrome c oxidation in Chromatium vinosum [4] and Rhodopseudomonas viridis [16] display temperature independence at low temperature, a herald of tunneling. The early Chromatium data were analyzed as a single phase, while the Rp. viridis data were analyzed into three phases, dominated by very fast (VF) and fast (F) phases at high temperatures, and dominated by slow (S) phase at low temperatures.

Cytochrome C 6-Bromo-2-naphthyl sulfate Cytochrome C (oxidized) 1.8 0.2 203... 

Fig. 24. Current models for the coordination geometries of the iron and copper centers in reduced cytochrome oxidases. Oxygen reduction occurs at the cytochrome fl3 /CuB " cluster cytochrome a and Cu are involved with cytochrome c oxidation. (From Babcock. )...

Figure 8. Spectra of cyctochrome c measured in a cell with an optically transparent electrode. Curve 1—cytochrome c reduced at < 0.3 V curve 2— cytochrome c oxidized at Er > 1.2 V curve 3—the initial solution of cytochrome c.

Figure 10. Plot of log [cytochrome c (reduced)/cytochrome c(oxidized)Jversus log [cytochrome c oxidase (reduced)/cytochrome c oxidase (oxidized)] for reductive indirect coulometric titration of cytochrome c-cyto-chrome c oxidase mixture. Data points taken from Figure 9 and solid line is computer calculation for the cytochrome c formal potential of 250 mV, the cytochrome c oxidase heme a formal potential of 210 mV, and the cytochrome c oxidase heme formal potential of 350 mV. Adapted from reference (60) with permission.

One other type of chemically modified electrode has been used in the study of cytochrome c, as described by Lewis and Wrighton. In this work platinum, gold, and p-type silicon substrates were modified with a polymeric overlayer which contained bipyridinium-type one-electron redox centers. These immobilized mediators transfer electrons between the electrode surface and diffusing ferricytochrome c at the potential of the mediators which is ca. 0.59 V more negative than the formal potential of cytochrome c. Oxidation of ferrocytochrome c is precluded because of the difference in the formal potentials of cytochrome c and the immobilized mediator. This same group has recently immobilized 2,3,4,5-tetramethyl-l-(dichlorosilylmethyl)-[2]-ferrocenophane on platinum. The juxtaposition of the formal potentials... 

The single cell green alga Chlorella produces a nitrate reductase that has been investigated by Kay et al The natural reductant is NADPH and in the presence of NR and NADPH the reduced NR enzyme is able to donate electrons to cytochrome c as evident from the appearance of a catalytic cytochrome c oxidation wave. Reduced MV and diquat were effective artificial electron donors to NR and in the presence of nitrate a catalytic reduction current was observed. 

Phenomenology of Cytochrome c Oxidation to Reduce Oxygen with... 

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