NADH oxidase system

In H. salinarium (cutinibnim), NADH is oxidized through c-type cytochromes and an cytochrome a oxidase. 2-heptyl-4-hydroxyquinoline-yV-oxide (HOQNO) inhibits electron transport chain at the level of the NADH dehydrogenase. The salt dependence of the NADH oxidase system indicates that the salt dependence of the NADH oxidase system is a reflection of the sensitivity of the NAD dehydrogenase [95]. 

H2O2-generating system which may be an NADPH (NADH) oxidase system similar to that of leukocytes (Chapter 15). Thyroperoxidase is a glycosylated heme enzyme that is bound to the apical plasma membrane of the thyrocyte. Thyroperoxidase exists in two molecular forms (M.W. 105,000 and 110,000) and its catalytic domain faces the colloid space. In thyroid autoimmune disorders, one of the major microsomal antigenic components is thyroperoxidase. 

Table 5. Example for factor analysis as pre-processing step in multiple regression analysis. Factor loadings (after varimax rotation) for the inhibition of the NADH-oxidase system by 17 ring-substituted phenoxyaeetie aeids. Only the high (signifieant non-zero) loadings are reported (from [1])...

On the basis of inhibition studies with antimycin, it has been postulated that coenzyme Q occupies, in the electron transport chain, a position intermediate between the succinate dehydrogenase flavoprotein and cytochrome c in the succinoxidase system, and between cytochrome b and cytochrome c in the NADH oxidase system. 

Similar to the work described by Spohn et al. [34], a trienzyme sensor was developed recently for the determination of branched-chain amino acids (L-valine, L-leucine, and L-isoleucine). Leucine dehydrogenase, NADH oxidase, and peroxidase were coimmobilized covalently on tresylate-hydrophylic vinyl polymer beads and packed into a transparent PILL tube (20 cm X 1.0 id), which was used as flow cell. The sensor was free of interferences from protein and NH4+ and it was stable for 2 weeks. The sensor system was applied to the determination of branched-chain amino acids in plasma with recoveries ranging from 98 to 100% [36],... 

Putidaredoxin. Cushman et al. (36) isolated a low molecular iron-sulfur protein from camphor-grown Pseudomonas putida. This protein, putidaredoxin, is similar to the plant type ferredoxins with two irons attached to two acid-labile sulfur atoms (37). It has a molecular weight of 12,000 and shows absorption maxima at 327, 425 and 455 nm. Putidaredoxin functions as an electron transfer component of a methylene hydroxylase system involved in camphor hydroxylation by P. putida. This enzyme system consists of putidaredoxin, flavoprotein and cytochrome P.cQ (38). The electron transport from flavoprotein to cytochrome P.cq is Smilar to that of the mammalian mixed-function oxidase, but requires NADH as a primary electron donor as shown in Fig. 4. In this bacterial mixed-function oxidase system, reduced putidaredoxin donates an electron to substrate-bound cytochrome P. g, and the reduced cytochrome P. g binds to molecular oxygen. One oxygen atom is then used for substrate oxidation, and the other one is reduced to water (39, 40). 

Three are the large functional subunits of cytochrome oxidase, one is cytochrome b, and seven are subunits of the NADH dehydrogenase system (Complex I). 

Oxidation is by far the most important Phase I metabolic reaction. One of the main enzyme systems involved in the oxidation of xenobiotics appears to be the so called mixed function oxidases or monooxygenases, which are found mainly in the smooth endoplasmic reticulum of the liver but also occur, to a lesser extent, in other tissues. These enzymes tend to be nonspecific, catalysing the metabolism of a wide variety of compounds (Table 9.2). Two common mixed function oxidase systems are the cytochrome P-450 (CYP-450) and the flavin monoxygenase (FMO) systems (Appendix 12). The overall oxidations of these systems take place in a series of oxidative and reductive steps, each step being catalysed by a specific enzyme. Many of these steps require the presence of molecular oxygen and either NADH or NADPH as co-enzymes. 

At least three types of proton channel systems are recognized in animal cells. These include the Na+/H+ exchanger, the H+-ATPase, and the HCOj/Cl- exchanger. It is clear that a major part of proton release by some cells in response to transplasma membrane electron transport is by activation of the Na+/H+ exchanger. This is clear from the characteristics of the proton movement elicited and the magnitude of H+ release in relation to electron flow when electron transport is activated. Activation of electron transport can be elicited by addition of di-ferric transferrin to activate the transmembrane NADH oxidase activity or by electron flow to external ferricyanide from internal NADH. Addition of di-ferric transferrin to certain cells, especially pineal cells, elicits a remarkable proton release and internal alkaliniza-tion. The stoichiometry of H+ release to iron reduced is more than 100 to 1 (Sun et... 

The myeloperoxldase/hallde system found In fish has been shown to produce elevated levels of superoxide anions and hydrogen peroxide which In turn randomly peroxldlzes the olefin bonds of fish lipids (37-38). The NADH-dependent oxidase system, which was Isolated as a membrane fraction from fish skeletal muscle, requires ADP and Iron Ions to Initiate hydroperoxidation, but Its mechanism of activity Is still unclear (33-36). 

Even if pulse radiolysis has been used [13], most studies of the initial electron entry into cytochrome oxidase are based on the finding that at low ionic strength cytochrome c forms a strong electrostatic complex with the oxidase [14]. Cytochrome c itself cannot be photoactivated, but in the complex with the enzyme it can be reduced by photochemically generated radicals, such as that of 5-diazariboflavin [15]. Another approach has been to employ a photoinduced uroporphyrin/NADH reduction system [16]. 

Both groups of reactions are found in bacteria (14), all higher animals (i5), and plants (16) however, oxidative phosphorylation is responsible for 90 % of the oxygen consumed (i 7). Oxidative phosphorylation is driven by the respiratory electron-transport system that is embedded in the lipoprotein inner membrane of eukaryotic mitochondria and in the cell membrane of prokaryotes. It consists of four complexes (Scheme I). The first is composed of nicotinamide adenine dinucleotide (NADH) oxidase, flavin mononucleotide (FMN), and nonheme iron-sulfur proteins 18,19), and it transfers electrons from NADH to ubiquinone. The second is composed of succinate dehydrogenase (SDH), flavin adenine dinucleotide (FAD), and nonheme iron-sulfur proteins (20), and it transfers electrons from succinate to ubiquinone 21, 22). The third is composed of cytochromes b and c, and nonheme iron-sulfur proteins (23), and it transfers electrons from ubiquinone (UQ) to cytochrome c 24). The fourth complex consists of cytochrome c oxidase [ferrocytochrome c 0 oxidoreductase EC 1.9.3.1 25)] which transfers electrons from cytochrome c to O2 26, 27). 

For example, reactions of xanthine oxidase have been shown to occur by both one-and two-electron mechanisms with oxygen [157,158] and benzoquinone [159] as electron acceptors. Production of superoxide from one-electron donation to oxygen has been demonstrated by rapid-freeze ESR studies [160]. The immobilized free radical species that was detected was identified as Oj by comparison with spectra obtained in chemical systems. However, the fraction of one-electron transfer that occurs depends [157] on a number of factors, including oxygen concentration, pH, and the concentration of the electron donor. The situation with benzoquinone is similarly complex quantitative ESR studies [159] have shown that the extent of one-electron reduction depends upon the concentration of benzoquinone if xanthine is used as donor, but not if NADH is used. In addition, with NADH the reaction is very pH dependent. The apparent Michaelis constant for benzoquinone is much smaller with xanthine than with NADH. Because of the complexities of the xanthine oxidase system, it would appear that data from studies involving acceptors other than oxygen or benzoquinone must be analyzed carefully if reliable conclusions are to be drawn regarding the reaction mechanism. 

Umezawa et al., 1982), or with fluorescence markers (Ishimori et al., 1984). The latter system was shown to be most sensitive, the detection limit being 10-15 mol/L Double signal amplification can be obtained by inclusion of enzymes in the liposomes (Brahman et al., 1984). Thus, Haga et al. (1980) entrapped HRP in sensitized liposomes and used the liposomes to determine theophylline. The rate of HRP liberation was monitored by measuring the NADH oxidase activity of HRP with an oxygen electrode. The electrode response correlated with the theophylline concentration in the sample between 4 and 20 nmol/L... 

Another interesting application of the Hb02 method is the determination of ethanol concentration in the presence of NAD+, alcohol dehydrogenase and bacterial NADH-oxidase as an indicator system (Figure 11). Since the standard curve is expressed in terms of the rate of oxygen consumption, the interval of linearity as well as the slope depend on the... 

Following the oral administration of Hg " " to animals, exhalation of Hg" vapor was observed (Sugata and Clarkson 1979), perhaps via the cytochrome c, NADPH and NADH, or by the xanthine oxidase systems (Ogata etal. 1987). There is no evidence for the methylation of Hg to MeHg by mammalians, though microorganisms in the gut flora may be responsible for this (Rowland et al. 1977). Hg" " is unstable in biological systems, and disassociates to Hg and Hg (Clarkson 1993). 

The compounds capsaicin and resiniferatoxin (both vanil-loids) inhibit the NADH-electron transport system, activate c-Jun kinase (JNK) but not API, and induce apoptosis in transformed cells (Macho et al. 1998). Capsaicin, dihydrocapsaicin, and resiniferatoxin inhibit NADH oxidase and induce apoptosis (Vaillant et al. 1996 Wolvetang et al. 1996). 

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