Dopamine-quinone

An example of such a catalytic EC process is the oxidation of dopamine in the presence of ascorbic acid (4). The dopamine quinone formed in the redox step is reduced back to dopamine by the ascorbate ion. The peak ratio for such a catalytic reaction is always unity. 

LaVoie, M.J., Hastings, T.G. Dopamine quinone formation and protein modification associated with the striatal neurotoxicity of methamphetamine evidence against a role for extracellular dopamine. J. Neurosci. 19 1484, 1999. 

Neurodegeneration, microglial activation BV-2 microglial cells Lipopolysaccharide, HIV protein TAT, dopamine quinone Gene ontology analysis of common pathway response [28]... 

Sidwell and Rechnitz (1985) placed a slice of banana pulp tissue on the gas-permeable membrane of a Clark-type oxygen electrode. The banana tissue contains polyphenol oxidase which catalyzes the oxidation of dopamine to dopamine quinone and further to melanin at the expense of oxygen. Wang and Lin (1988) integrated this biocatalytic phase in the electrode body of a membrane-free carbon paste electrode and measured the formation of dopamine quinone at a potential of -0.2 V. This arrangement permitted selective determination of dopamine in the presence of ascorbic acid with a response time of only 12 s. It seems likely that this improved performance of a tissue-containing sensor could be extended to other analytes. 

Fenoldopam (76) is an antihypertensive renal vasodilator apparently operating through the dopamine system. It is conceptually similar to trepipam. Fenoldopam is superior to dopamine itself because of its oral activity and selectivity for dopamine D-1 receptors (D-2 receptors are as.sociated with emesis). It is synthesized by reduction of 3,4-dimethoxyphenylacetonitrile (70) to dimethoxyphenethylamine (71). Attack of diis last on 4-methoxystyrene oxide (72) leads to the product of attack on the epoxide on the less hindered side (73). Ring closure with strong acid leads to substituted benzazepine 74. O-Dealkylation is accomplished with boron tribromide and the catechol moiety is oxidized to the ortho-quinone 75. Treatment with 9NHC1 results in conjugate (1,6) chloride addition and the formation of fenoldopam (76) [20,21]. 

The oxidation of N ADH has been mediated with chemically modified electrodes whose surface contains synthetic electron transfer mediators. The reduced form of the mediator is detected as it is recycled electrochemically. Systems based on quinones 173-175) dopamine chloranil 3-P-napthoyl-Nile Blue phenazine metho-sulphatemeldola blue and similar phenoxazineshave been described. Conducting salt electrodes consisting of the radical salt of 7,7,8,8-trtra-cyanoquinodimethane and the N-methylphenazium ion have been reported to show catalytic effects The main drawback to this approach is the limited stability... 

Graham, D.G. Tiffany, S.M. Bell, W.R., Jr. and Gutknecht, W.F. Autooxidation versus covalent binding of quinones as the mechanism of toxicity of dopamine, 6-hydroxydopamine and related compounds toward C1300 neuroblastoma cells in vitro. Mol Pharmacol 14 644-653, 1978. 

Drosophila Ddc is expressed primarily in the CNS and the hypoderm, the epithelial layer of the fly that secretes the cuticle. In the CNS, Ddc is expressed in a small subset of neurons that produce either dopamine or serotonin (Budnik and White, 1988 Valles and White, 1988). In the hypoderm, Ddc expression leads to synthesis of dopamine, which is further metabolized into quinones that have a vital function in the cross-linking, hardening, and pigmentation of the fly cuticle (Wright, 1987). The developmental profile of DDC activity in these two tissues is quite different (Hirsh, 1986). DDC is first detected during late embryo-... 

Studies of the oxidation products of catecholamines (i.e., seretonin, dopamine, dopa, adrenaline, and noradrenaline) have indicated that protein oxidation by quinones may lead to apoptosis. Oxidation results in formation of orrto-quinones, which contribute to cytotoxicity and have been suggested... 

Tyrosinase is a monooxygenase which catalyzes the incorporation of one oxygen atom from dioxygen into phenols and further oxidizes the catechols formed to o-quinones (oxidase action). A comparison of spectral (EPR, electronic absorption, CD, and resonance Raman) properties of oxy-tyrosinase and its derivatives with those of oxy-Hc establishes a close similarity of the active site structures in these proteins (26-29). Thus, it seems likely that there is a close relationship between the binding of dioxygen and the ability to "activate" it for reaction and incoiporation into organic substrates. Other important copper monooxygenases which are however of lesser relevance to the model studies discussed below include dopamine p-hydroxylase (16,30) and a recently described copper-dependent phenylalanine hydroxylase (31). 

Hydroquinones. - 3,4-Dihydroxyphenylacetic acid, a metabolite of the neurotransmitter dopamine, has been shown to undergo oxidation by "NO to a semiquinone, which was observed by EPR upon spin stabilisation with Mg2+ ions.119 Formation of the radical may be a crucial event in the development of Parkinson s disease (section 18.3). 4-Hydroxyestradiol, which has been implicated in breast cancer, is oxidised to a semiquinone by HRP. Mutagenicity is believed to result from addition of the quinone metabolite to DNA.120... 

The half-wave potential for the electrochemical oxidation of NADH to NAD is ca. -bO.6 V vj. SCE at pH 7. The formal potential for the NADH/NAD couple, however, is only —0.56 V. The overpotential therefore is about 1.2 V. As NAD acts as coenzyme in many enzyme-catalyzed oxidations of practical importance, it would be of interest to regenerate NAD electrochemically. For this purpose it is necessary to find a mediator system which is able to lower the overpotential. Mediator systems accepting two electrons or a hydride atom are most effective. Therefore, dopaquinone electro-generated from dopamine 2" and quinone diimines derived from diaminobenzenes applied successfully. 

This selectively neurotoxic compound damages the sympathetic nerve endings. Because of its structural similarity to dopamine, it is actively taken up into the synaptic system. Once taken up, it oxidizes to a reactive quinone, which may bind to protein and produce reactive free radicals and superoxide. These events destroy the nerve terminals and nerve cells also in some cases. 

Oxidation with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) of the thiourea 51, derived from dopamine, gave the 1,3-benzothiazepine 53 in quantitative yield via a facile J-based nucleophilic intramolecular addition to the intermediate o-quinone 52 (Equation 9) <2005OBC2387>. 

Electrochemical oxidation of some catecholamines such as dopamine, L-dopa, and methyldopa has been studied using cyclic voltammetry. The catecholamines undergo intramolecular cyclization to form the corresponding o-quinone derivatives. The significant differences in the electrochemical behaviour of the catecholamines have been attributed to the effects of the side-chain carboxyl group.253 Electron-transfer reactions of 2,-deoxyguanosine-5,-monophosphate (dGMP) in phosphate buffers by cyclic... 

Catechol oxidation catalyzed by peroxidases can be used not only for the synthesis of sulfur-substituted catechols but also for the preparation of synthetic compounds related to pheomelanins, which contain benzothiazine units. In fact, the quinone undergoes an extremely easy nucleophilic addition by thiols. For example, treating the neurotransmitter dopamine with cysteine, in the presence of HRP/H2O2, gives rise to 2-S- and 5-5-cysteinyl-catecholamine and a smaller amount of the 2-S,5-S,-di-cysteinyl-catecholamme conjugate [48, 49] (Fig. 6.3e). 

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