Cytochrome oxidation-reduction

The abihty of iron to exist in two stable oxidation states, ie, the ferrous, Fe ", and ferric, Fe ", states in aqueous solutions, is important to the role of iron as a biocatalyst (79) (see Iron compounds). Although the cytochromes of the electron-transport chain contain porphyrins like hemoglobin and myoglobin, the iron ions therein are involved in oxidation—reduction reactions (78). Catalase is a tetramer containing four atoms of iron peroxidase is a monomer having one atom of iron. The iron in these enzymes also undergoes oxidation and reduction (80). 

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. 

Chlorophyll, plastoquinone, and cytochrome are complicated molecules, but each has an extended pattern of single bonds alternating with double bonds. Molecules that contain such networks are particularly good at absorbing light and at undergoing reversible oxidation-reduction reactions. These properties are at the heart of photosynthesis. 

Correlations between Lucigenin-Amplified CL and SOD-Inhibited Cytochrome c Reduction or Epinephrine Oxidation... 

Vermilion, J.L. and Coon, M.J. (1978) Purified liver microsomal NADPH-cytochrome P-450 reductase. Spectral characterization of oxidation-reduction states. Journal of Biological Chemistry, 253 (8), 2694-2704. 

Flavoprotein dehydrogenases usually accept electrons from reduced pyridine nucleotides and donate them to a suitable electron acceptor. The oxidation-reduction midpoint potential of the FAD of the oxidase has been determined by ESR spectroscopy and shown to be -280 mV. The NADP+/ NADPH redox potential is -320 mV and that of the cytochrome b is -245 mV hence, the flavin is thermodynamically capable of accepting electrons from NADPH and transferring them to cytochrome b. As two electrons are transferred from NADPH, although O2 reduction requires only one electron, the scheme of electron transfer shown in Figure 5.8 has been proposed by Cross and Jones (1991). 

Cross, A. R., Harper, A. M., Segal, A. W. (1981). Oxidation-reduction properties of the cytochrome b found in the plasma-membrane fraction of human neutrophils. Biochem. J. 194, 599-606. 

The first electrochemical studies of Mb were reported for the horse heart protein in 1942 (94) and subsequently for sperm whale Mb (e.g., 95) through use of potentiometric titrations employing a mediator to achieve efficient equilibriation of the protein with the electrode (96). More recently, spectroelectrochemical measurements have also been employed (97, 98). The alternative methods of direct electrochemistry (99-102) that are used widely for other heme proteins (e.g., cytochrome c, cytochrome bs) have not been as readily applied to the study of myoglobin because coupling the oxidation-reduction eqiulibrium of this protein to a modified working electrode surface has been more difficult to achieve. As a result, most published electrochemical studies of wild-type and variant myoglobins have involved measurements at eqiulibrium rather than dynamic techniques. 

The oxidation/reduction of redox cofactors in biological systems is often coupled to proton binding/release either at the cofactor itself or at local amino acid residues, which provides the basic mechanochem-ical part of a proton pump such as that foimd in cytochrome c oxidase (95). Despite a thermodynamic cycle that provides that coupling of protonation of amino acids to the reduction process will result in a 60 mV/pH decrease unit in the reduction potential per proton boimd between the pAa values in the Fe(III) and Fe(II) states, the essential pumping of protons in the respiratory complexes has yet to be localized within their three-dimensional structures. 

Porphyrin rings containing iron are also a feature of the cytochromes. Several cytochromes are responsible for the latter part of the electron transport chain of oxidative phosphorylation that provides the principal source of ATP for an aerobic cell (see Section 15.1.2). Their function involves alternate oxidation-reduction of the iron between Fe + (reduced form) and Fe + (oxidized form). The individual cytochromes vary structurally, and their classification (a, b, c, etc.) is related to their absorption maxima in the visible spectrum. They contain a haem system that is covalently bound to protein through thiol groups. 

Metal ions in the form of organometallic complexes such as the iron atom in heme can undergo one-electron transfers in oxidation-reduction reactions catalyzed by oxidoreductases with associated cytochromes. 

An elemental analysis of cytochrome c, an enzyme involved in oxidation reduction process, gave 0.43% Fe and 1.48% S. The minimum molecular weight of enzyme and The Minimum Number of Iron Atoms per Molecule of Sulphur Atom. 

Phase I metabolic reactions involve oxidation, reduction, or hydrolysis of the parent molecule, resulting in the formation of a more polar compound. Phase 1 reactions are mediated by the cytochrome P450 (GYP) family of enzymes. While metabolism used to be thought of as the body s detoxification process, phase I metabolites may be equally or even more pharmacologically active than the parent compound. Drug metabolism in general, and CYP-based mechanisms in particular, are discussed in detail in Chapter 5. 

The first stage 1 reaction i.e. oxidation-reduction are generated by a common hydroxy-lating enzyme system (cytochrome P450 system CYP), which is located in... 

The fact that the cytochrome P-450 was induced even in the presence of NH3, which is the end product of assimilatory N-oxide reductions, suggested that it might funciton in dissimilatory N-oxide reductions. Anaerobic growth experiments with induced cells showed that reduction of nitrate to nitrite was energy yielding in F. oxysporum but reduction of nitrite to N2O was probably not (Shoun and Tanimoto, 1991). 

The liver is the principal site of drug metabolism. Hepatic drug metabolism is usually classified into two distinct phases. Phase I reactions are oxidation, reduction or hydrolysis. One of the most important systems that catalyse oxidation are the haem-containing cytochrome P-450 enzymes. 

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