Nicotinamide adenine dinucleotide radicals

Photodissociation of dimer coupled to current measurement of electrochemical oxidation of the pyridinyl radical to the pyridinium ion has been described in Section 3.1.3. Oxidation of the l-methyl-3-carbamidopyridinyl and NAD (nicotinamide adenine dinucleotide radical) after dissociation of the dimers has been reported the agents being either oxygen or OH radical. Reasonable mechanisms for the latter are either electron transfer or radical combination, followed by dissociation to Py+ and OH. 

The basicity of pyridinyl radicals is of interest since some pyridinyl radicals react with one another in an acid catalyzed reaction (sect. 4.4). The absorption spectra of radicals generated from the pyridinium ion by pulse radiolysis in aqueous solution at different pH values allow the evaluation of the basicity of the radicals 97,98) I jjg Qf protonated form of l-methyl-3-carbamidopyridinyI radical, (CONHj) ), is 1.43 the protonated radical has alsorption maxima at 3(X) nm and 440 nm, at somewhat longer wavelengths than those for the unprotonated radical at 280 nm and 420 nm. The nicotinamide adenine dinucleotide radical (NAD ) has a pK, of 0 or less, with a shift in absorption maximum due to protonation being observed only in 1.5 M HCIO4. 

Kobayashi et al. (169) smdied the reduction of the parental enzyme, XDH, by several different free radicals produced by PR Salicylate anion radicals (SL ), nicotinamide adenine dinucleotide radicals (NAD ), and 1-methylnicotinamide radicals (1-MNA ). These free radicals are potential substrates that interact with... 

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. 

Boron also appears to be involved in redox metabolism in cell membranes. Boron deficiency was shown to inhibit membrane H -ATPase isolated from plant roots, and H -ATPase-associated proton secretion is decreased in boron-deficient cell cultures [71]. Other studies show an effect of boron on membrane electron transport reactions and the stimulation of plasma reduced nicotinamide adenine dinucleotide (NADH) oxidase upon addition of boron to cell cultures [72, 73]. NADH oxidase in plasma membrane is believed to play a role in the reduction of ascorbate free radical to ascorbate [74]. One theory proposes that, by stimulating NADH oxidase to keep ascorbate reduced at the cell wall-membrane interface, the presence of boron is important in... 

Triazine (e.g., atrazine, simazine) and substituted urea (e.g., diuron, monuron) herbicides bind to the plastoquinone (PQ)-binding site on the D1 protein in the PS II reaction center of the photosynthetic electron transport chain. This blocks the transfer of electrons from the electron donor, QA, to the mobile electron carrier, QB. The resultant inhibition of electron transport has two major consequences (i) a shortage of reduced nicotinamide adenine dinucleotide phosphate (NADP+), which is required for C02 fixation and (ii) the formation of oxygen radicals (H202, OH, etc.), which cause photooxidation of important molecules in the chloroplast (e.g., chlorophylls, unsaturated lipids, etc.). The latter is the major herbicidal consequence of the inhibition of photosynthetic electron transport. 

Many 1-alkyl-l-hydropyridinyl radicals are not persistent in aqueous medium. The bimolecular decay reaction has been investigated for 66 and 70 and a mechanism consistent with products and kinetics advanced.239 The reactions of 70, its 3-carboxamide isomer, and the pyridinyl radical derived from nicotinamide adenine dinucleotide (NAD) with cytochrome c have been investigated by pulse radiolysis and rates established.240... 

As shown in Figure 13.3, oxidation of ascorbic acid, for example, by the reduction of superoxide to hydrogen peroxide or Fe + to Fe +, and similar reduction of other transition metal ions, proceeds by a one-electron process, forming the monodehydroascorbate radical. The radical rapidly disproportionates into ascorbate and dehydroascorbate. Most tissues also have both nicotinamide adenine dinucleotide phosphate (NADPH) and glutathione-dependent monodehydroascorbate reductases, which reduce the radical back to ascorbate. Ascorbate is thus an effective quencher of singlet oxygen and other radicals. 

A pulse of 2-10 Mev electrons from a linear accelerator, passed through aqueous solutions of pyridinium ions leads rapidly to substantial concentrations of pyridinyl radicals , including those derived from the coenzyme, nicotinamide adenine dinucleotide . The pyridinyl radicals disproportionate, are protonated or dimerize. The reducing agent is a solvated electron or the COj" radical anion (Eq. 4) . 

FIGURE 29-1. Schematic of the interaction of oxygen radicals and the antioxidant system. GSH = glutathione G6PD = glucose-6-phosphate dehydrogenase NADP = nicotinamide-adenine dinucleotide phosphate NADPH = reduced NADP. 

B15. Bielski, B. H. J., and Chan, P. C., Kinetic study by pulse radiolysis of the lactate dehydrogenase catalyzed chain oxidation of nicotinamide adenine dinucleotide by H02 and 0 radical. J. Biol. Chem. 250, 318-321 (1975). 

NADP (nicotinamide adenine dinucleotide phosphate), storing the reducing power in the form of NADPH. The chlorophyll ion can regain an electron from a hydroxyl ion (OH ), which is also formed during the self-ionization of water, and the resulting hydroxyl radical (OH-, which has no charge) combines with others to form oxygen and water. 

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