Cytochrome oxidase, reduction

Fe Cytochrome oxidase reduction of oxygen to water Cytochrome P-450 0-insertion from O2, and detoxification Cytochromes b and c electron transport in respiration and photosynthesis Cytochrome f photosynthetic electron transport Ferredoxin electron transport in photosynthesis and nitrogen fixation Iron-sulfur proteins electron transport in respiration and photosynthesis Nitrate and nitrite reductases reduction to ammonium... 

The oxygen transporting capacity of SNO-PEG-Hb was evaluated using a hemorrhagic shock model in rats by monitoring the redox state of cytochrome oxidase reduction of cerebral tissues, in which a near-infrared spectroscopy... 

FIGURE 21.20 A model for the mechanism of O9 reduction by cytochrome oxidase. 

Write a balanced equation for the reduction of molecular oxygen by reduced cytochrome e as carried out by complex IV (cytochrome oxidase) of the electron transport pathway. 

The mechanism of reduction of dioxygen by fully reduced cytochrome oxidase. Correlation of room and low temperature studies. G. M. Clore, Rev. Inorg. Chem., 1980,2, 343-360 (52). 

The cytochromes are iron-containing hemoproteins in which the iron atom oscillates between Fe + and Fe + during oxidation and reduction. Except for cytochrome oxidase (previously described), they are classified as dehydrogenases. In the respiratory chain, they are involved as carriers of electrons from flavoproteins on the one hand to cytochrome oxidase on the other (Figure 12-4). Several identifiable cytochromes occur in the respiratory chain, ie, cytochromes b, Cp c, a, and (cytochrome oxidase). Cytochromes are also found in other locations, eg, the endoplasmic reticulum (cytochromes P450 and h, and in plant cells, bacteria, and yeasts. 

The prevalence of the heme in O2 metabolism and the discovery in the 1960s that metallophthalocyanines adsorbed on graphite catalyze four-electron reduction of O2 have prompted intense interest in metaUoporphyrins as molecular electrocatalysts for the ORR. The technological motivation behind this work is the desire for a Pt-ffee cathodic catalyst for low temperature fuel cells. To date, three types of metaUoporphyrins have attracted most attention (i) simple porphyrins that are accessible within one or two steps and are typically available commercially (ii) cofacial porphyrins in which two porphyrin macrocycles are confined in an approximately stacked (face-to-face) geometry and (iii) biomimetic catalysts, which are highly elaborate porphyrins designed to reproduce the stereoelectronic properties of the 02-reducing site of cytochrome oxidase. 

Boulatov R. 2004. Understanding the reaction that powers this world Biomimetic studies of respiratory O2 reduction by cytochrome oxidase. Pure Appl Chem 76 303. 

Boulatov R, Collman JP, Shiryaeva IM, Sunderland CJ. 2002. Functional analogs of the O2 reduction site of cytochrome oxidase Mechanistic aspects and possible effects of Cug. J Am Chem Soc 124 11923... 

Collman JP, Boulatov R. 2002. Electtocatal3dic O2 reduction by S3mthetic analogs of the heme/ Cu site of cytochrome oxidase incorporated in a Upid film. Angew Chem Int Ed 41 3487. 

P. Mitchell (Nobel Prize for Chemistry, 1978) explained these facts by his chemiosmotic theory. This theory is based on the ordering of successive oxidation processes into reaction sequences called loops. Each loop consists of two basic processes, one of which is oriented in the direction away from the matrix surface of the internal membrane into the intracristal space and connected with the transfer of electrons together with protons. The second process is oriented in the opposite direction and is connected with the transfer of electrons alone. Figure 6.27 depicts the first Mitchell loop, whose first step involves reduction of NAD+ (the oxidized form of nicotinamide adenosine dinucleotide) by the carbonaceous substrate, SH2. In this process, two electrons and two protons are transferred from the matrix space. The protons are accumulated in the intracristal space, while electrons are transferred in the opposite direction by the reduction of the oxidized form of the Fe-S protein. This reduces a further component of the electron transport chain on the matrix side of the membrane and the process is repeated. The final process is the reduction of molecular oxygen with the reduced form of cytochrome oxidase. It would appear that this reaction sequence includes not only loops but also a proton pump, i.e. an enzymatic system that can employ the energy of the redox step in the electron transfer chain for translocation of protons from the matrix space into the intracristal space. 

How does nature prevent the release of hydrogen peroxide during the cytochrome oxidase-mediated four-electron reduction of dioxygen It would appear that cytochrome oxidase behaves in the same manner as other heme proteins which utilize hydrogen peroxide, such as catalase and peroxidase (vide infra), in that once a ferric peroxide complex is formed the oxygen-oxygen bond is broken with the release of water and the formation of an oxo iron(IV) complex which is subsequently reduced to the ferrous aquo state (12). Indeed, this same sequence of events accounts for the means by which oxygen is activated by cytochromes P-450. 

Superoxide-dismuting activity of copper rutin complex was confirmed by comparison of the inhibitory effects of this complex and rutin on superoxide production by xanthine oxidase and microsomes (measured via cytochrome c reduction and by lucigenin-amplified CL, respectively) with their effects on microsomal lipid peroxidation [166]. An excellent correlation between the inhibitory effects of both compounds on superoxide production and the formation of TBAR products was found, but at the same time the effect of copper rutin complex was five to nine times higher due to its additional superoxide dismuting capacity. 

Values (p.mol I-1) for Inhibitory Effects of Metal-Rutin Complexes and Rutin on Cytochrome c Reduction by Xanthine Oxidase (I), Iron-Catalyzed Microsomal Lipid Peroxidation (II), and Lucigenin-Amplified Microsomal CL (III) [167]... 

Possible errors due to the competition of cytochrome c reduction with the reversible reduction of quinones by superoxide are frequently neglected. For example, it has been found that quinones (Q), benzoquinone (BQ), and menadione (MD) enhanced the SOD-inhibitable cytochrome c reduction by xanthine oxidase [6]. This seems to be a mystery because only menadione may enhance superoxide production by redox cycling ( °p)"]/ [MD] =-0.20 V against ,0[02 ]/[02] 0.16 V) via Reactions (3) and (4), whereas for... 

Proteins involved in the fundamental structure and function of neurons are decreased in schizophrenia. Several postmortem studies have identified consistent reductions in the expression of mitochondrial associated genes involved in oxidative metabolism, such as cytochrome oxidase and cytochrome C reductase [23], Reduced oxidative metabolism is consistent with evidence of increased brain lactate,... 

Intravenous injection, constant infusion of 0.15-0.20 mg CN/kg BW per min LD50 in about 20 min rapid progressive reduction in cerebrocortical cytochrome oxidase (cytochrome aa3) concomitant with increases up to 200% in cerebral blood flow 30... 

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