NADPH oxidases dinucleotide phosphate oxidase

Overproduction of superoxide ( Op has been implicated in the pathogenesis of various cardiovascular diseases. The main sources of human superoxide include the nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase) enzyme complex, cyclooxygenase, mitochondrial oxidases, xanthine oxidase, and nitric... 

Hexachloroethane is metabolized by the mixed function oxidase system by way of a two-step reduction reaction involving cytochrome P-450 and either reduced nicotinamide adenine dinucleotide phosphate (NADPH) or cytochrome b5 as an electron donor. The first step of the reduction reaction results in the formation of the pentachloroethyl free radical. In the second step, tetrachloroethene is formed as the primary metabolite. Two chloride ions are released. Pentachloroethane is a minor metabolic product that is generated from the pentachloroethyl free radical. 

The answers are 34-g, 33-a, 36-d. (Katzung, pp 53-56.) There are four major components to the mixed-function oxidase system (1) cytochrome P450, (2) NADPH, or reduced nicotinamide adenine dinucleotide phosphate, (3) NADPH-cytochrome P450 reductase, and (4) molecular oxygen. The figure that follows shows the catalytic cycle for the reactions dependent upon cytochrome P450. 

Enzymes responsible for metabolism are located at various subcellular sites, for example the cytosol, mitochondria and smooth endoplasmic reticulum. However, it is enzymes derived from endoplasmic reticulum, called mixed function oxidases or monooxygenases , which have been most intensely studied in the past two or three decades. These enzyme systems, which utilize a family of haemoprotein cytochromes, or P-450 as terminal oxidases, require molecular oxygen and reduced nicotinamide adenine dinucleotide phosphate (NADPH) for activity. The overall stoichiometry of the reactions catalyzed by these enzymes is normally represented by equation (1). 

Reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is an enzymatic complex considered the most important source of superoxide... 

The hepatic endoplasmic reticulum possesses oxidative enzymes called mixed-function oxidases or monooxygenase with a specific requirement for both molecular oxygen and a reduced concentration of nicotinamide adenine dinucleotide phosphate (NADPH). Essential in the mixed-function oxidase system is P-450 (Figure 1.12). The primary electron donor is NADPH, whereas the electron transfer involved P-450, a flavoprotein. The presence of a heat-stable fraction is necessary for the operation of the system. 

Conditions for cytosolic incubations depend on the aim of the assay e.g. to cover specific enzymatic activity present in the cytosol. For this purpose it is essential to fortify the incubation medium with the specific cofactor for the reaction-if needed (Ekins 1999). (J> -Nicotinamide adenine dinucleotide (NAD) is needed for alcohol and aldehyde dehydrogenases, flavin adenine dinucleotide (FAD) for polyamine oxidase, P-nicotinamide adenine dinucleotide phosphate (NADPH) for Dihydropyrimidine dehydrogenase. Phase II reactions depend on PAPS (sulfotransferases,... 

Fig. 15. pH dependence of NADPH oxidase, NADPH to 3-acetylpyridine adenine dinucleotide (AP-DPN) transhydrogenase, and NADH oxidase activities of submito-chondrial particles (ETP). Conditions oxidase activities were measured in the presence of 2 mM NADH or NADPH, 0.25 M sucrose, 100 mM sodium phosphate for pH values 6-0, and 100 mM sodium acetate for pH values 5.0 and 5.5. ETP concentration was 2.16 mg/ml for the NADPH oxidase, and 0.216 mg/ml for the NADH oxidase assays. The transhydrogenase reaction was measured by the Aminco-Chance spectrophotometer at 400 minus 450 nm. The extinction coefficient used for reduced 3-acetylpyridine adenine dinucleotide at 400 nm was 2300 liters mole" cm" . Media were the same as in the oxidase assays. Dotted lines indicate uncertainty about the pH 5 rates because of possible acidity damage to ETP. The ordinate refers to nanomoles of NADPH or NADH oxidized min" x mg" of ETP protein at 30°. From Hatefi and Hanstein (,S0). 

Fig. 17. Effect of trypsin on the NADH oxidase, NADPH oxidase and the NADPH-to-NAD transhydrogenase activities of submitochondnal particles. The particles suspended in 0.26 M sucrose and 100 mAf sodium phosphate, pH 7.0, were treated with 0.1 mg trypsin per mg particle protein and incubated at (a) 0° or (b) 30°. At the intervals shown samples were removed and assayed at pH 6.0 and 7.0 for the activities shown. Transhydrogenase activity was measured either directly by reduction of 3-acetylpyridine adenine dinucleotide at 376 nm in the presence of cyanide-treated particles or by the increase in the rate of NADPH oxidation by submitochondrial particles after the addition of NAD. (A) NADH —> O2, ( ) NADPH —> Oi, and (O) NADPH —> NAD. From Djavadi-Ohaniance and Hatefi...

Production of ROS, factors involved in the aging process (Finkel and Holbrook, 2000), is elevated in AD brain and may be an important cause of AD (Martins et al., 1986). Elevated levels of oxicUzed hpids (lipid peroxidation, maloncUaldehyde, 4-hydroxynonenal) (Markesbery and Carney, 1999), proteins (advanced glycation end product mocUfications, tyrosine nitration) (Good et al., 1996 Takeda et al., 1998), and nucleic acids (8-hydroxy-deoxyguanosine) have been documented in AD brains (Lyras et al., 1997). Mitochondria and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex... 

NADPH oxidase nicotinamide adenine dinucleotide phosphate oxidase, a primary producer of reactive oxygen species. 

In vitro metabolic studies with rodent and human liver microsomal prepara- tions have established that MPTP undergoes both oxidative N-demethylation and C-6 (allylic) oxidation in reactions that are -nicotinamide adenine dinucleotide phosphate (NADPH) dependent and therefore likely to be cytochrome P-450 catalyzed (Weissman et al. 1985 Ottoboni et al. 1990). Although the latter transformation can lead to the toxic pyridinium metabolite MPP, the cytochrome P450-catalyzed pathway is unlikely to contribute significantly to the neurotoxicity of MPTP. As mentioned above, liver aldehyde oxidase diverts the inter-mediate dihydropyridinium metabolite away from pyridinium ion formation by catalyzing the conversion of structure 40 to the nontoxic lactim structure 41. Further-more, even if formed in the periphery, the polar pyridinium metabolite would have limited access to the central nervous system (CNS). The low... 

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