Oxidation catecholamine

The formation of aminochromes by the oxidation of catecholamines is usually a very rapid process. However, recent work has suggested that some of the highly reactive intermediate species, which are formed during the initial stages of the catecholamine oxidations and which have been largely overlooked in the past, may be of considerable physiological importance. 

The interaction of unspecified catecholamine oxidation products with certain sulfhydryl compounds, including cysteine, glutathione, and coenzyme A, has been studied by Roston.85- 88 It appeared that... 

The aminochromes are intermediates in the formation of the dark pigments known as the melanins, i.e. the final products of catecholamine oxidation. However, aminochromes can be converted into melanins both by oxidative and non-oxidative processes (see Section V, A). 

Figure 14 Experiments with a carbon fiber electrode at a single adrenal chromaffin cell exposed to 50 pM histamine for 5 s (indicated by the long bar). A 3 s exposure to a solution containing 100 nM Ca + and 50 pM epinephrine was used to postcalibrate the microsensor (shown by the short bar). In panel A, release from a single cell was evoked by histamine exposure and resulted in the amperometric spikes due to catecholamine oxidation (lower panel). At the same time, Ca release was detected. In panel B, neither catecholamine nor Ca - release was detected from a single cell after histamine exposure. I is the fluorescence intensity. Data were obtained using a 5pm carbon fiber electrode held at 0.65 V vs. SSCE. (Reproduced from Anal. Client, with permission [45].)...

Ceruloplasmin, another copper containing protein with some enzymic activity, is also a good catalyst for catecholamine oxidation and this particular reaction has received a considerable amount of attention during the last decade. When adrenaline or noradrenaline was added to ceruloplasmin, in... 

It is of interest to note that catecholamine oxidation products have been shown to inhibit an in vitro amino acid polymerisation system from rat brain [383] and to inhibit polypeptide synthesis in E. coli [384]. 

Identification, isolation, and removal of (polyhydroxy)benzenes from the environment have received increased attention throughout the 1980s and 1990s. The biochemical activity of the benzenepolyols is at least in part based on thek oxidation—reduction potential. Many biochemical studies of these compounds have been made, eg, of enzymic glycoside formation, enzymic hydroxylation and oxidation, biological interactions with biochemically important compounds such as the catecholamines, and humic acid formation. The range of biochemical function of these compounds and thek derivatives is not yet fully understood. 

Two important pathways for catecholamine metaboHsm are 0-methylation by COMT, which is cytoplasmicaHy localized, and oxidative deamination by the mitochondrial localized enzyme MAO. There are large amounts of MAO in tissues such as the fiver and the heart which are responsible for the removal of most of the circulating monoamine, including some taken in from the diet. Tyramine is found in high concentrations in certain foods such as cheese, and in wine. Normally, this tyramine is deaminated in the fiver. However, if MAO is inhibited, the tyramine may then be converted into octopamine [104-14-37] which may indirecdy cause release of NE from nerve terminals to cause hypertensive crisis. Thus MAO, which is relatively nonspecific, plays an important role in the detoxification of pharmacologically active amines ingested from the diet. 

Hynes MD, Berkowitz BA Catecholamine mechanisms in the stimulation of mouse locomotor activity hy nitrous oxide and morphine. Eur J Pharmacol 90 109-114, 1983... 

Dopamine (5-hydroxylase is a copper-containing enzyme involved in the synthesis of the catecholamines norepinephrine and epinephrine from tyrosine in the adrenal medulla and central nervous system. During hy-droxylation, the Cu+ is oxidized to Cu " reduction back... 

During ischaemia, the activity of cellular antioxidant systems may be reduced (Ferrari et al. 1985 GaUnanes etal. 1992). In addition, a number of cellular pathways that produce free radicals are primed during ischaemia such as the xanthine/xanthine oxidase system (McCord, 1987), catecholamine auto-oxidation (Jackson et al., 1986) and the arachadonic acid pathway (Halliwell and Gutteridge, 1989). Thus, during early reperfusion there is a burst of free radical production (see Fig. 4.1) that may overwhelm the antioxidant systems of the cells. 

Graham, D.G. Oxidative pathways for catecholamines in the genesis of neuromelanin and cytotoxic quinones. Mol Pharmacol 14 633-643. 1978. Hotchkiss, A.J., and Gibb, J.W. Long-term effects of multiple doses of methamphetamine on tryptophan hydroxylase and tyrosine hydroxylase activity in rat brain. J Pharmacol Exp Ther 214 257-262, 1980. 

Multiple electrodes have been used to obtain selectivity in electrochemical detection. An early example involved the separation of catecholamines from human plasma using a Vydac (The Separation Group Hesperia, CA) SCX cation exchange column eluted with phosphate-EDTA.61 A sensor array using metal oxide-modified surfaces was used with flow injection to analyze multicomponent mixtures of amino acids and sugars.62 An example of the selectivity provided by a multi-electrode system is shown in Figure 2.63... 

Electrochemical biosensors based on detection of hydrogen peroxide at platinized electrodes were found to be more versatile allowing a decrease in detection limit down to 1 i,mol L 1 [109]. However, all biological liquids contain a variety of electrochemically easily oxidizable reductants, e.g. ascorbate, urate, bilirubin, catecholamines, etc., which are oxidized at similar potentials and dramatically affect biosensor selectivity producing parasitic anodic current [110]. 

The most commonplace substrates in energy-transfer analytical CL methods are aryl oxalates such as to(2,4,6-trichlorophenyl) oxalate (TCPO) and z s(2,4-dinitrophenyl) oxalate (DNPO), which are oxidized with hydrogen peroxide [7, 8], In this process, which is known as the peroxyoxalate-CL (PO-CL) reaction, the fluorophore analyte is a native or derivatized fluorescent organic substance such as a polynuclear aromatic hydrocarbon, dansylamino acid, carboxylic acid, phenothiazine, or catecholamines, for example. The mechanism of the reaction between aryl oxalates and hydrogen peroxide is believed to generate dioxetane-l,2-dione, which may itself decompose to yield an excited-state species. Its interaction with a suitable fluorophore results in energy transfer to the fluorophore, and the subsequent emission can be exploited to develop analytical CL-based determinations. 

Sensitive electrochemical techniques have also been developed to directly measure the release of oxidizable neurotransmitters such as catecholamines (CAs) and serotonin (5-hydroxytryptamine, 5-HT). Current flows in the circuit when the potential of the electrode is positive enough to withdraw electrons from, i.e. oxidize, the released neurotransmitter. The technique is very sensitive and readily detects the release of individual quanta of neuro transmitter resulting from the fusion of single secretory vesicles to the plasmalemma (Fig. 10-2). 

Copper is part of several essential enzymes including tyrosinase (melanin production), dopamine beta-hydroxylase (catecholamine production), copper-zinc superoxide dismutase (free radical detoxification), and cytochrome oxidase and ceruloplasmin (iron conversion) (Aaseth and Norseth 1986). All terrestrial animals contain copper as a constituent of cytochrome c oxidase, monophenol oxidase, plasma monoamine oxidase, and copper protein complexes (Schroeder et al. 1966). Excess copper causes a variety of toxic effects, including altered permeability of cellular membranes. The primary target for free cupric ions in the cellular membranes are thiol groups that reduce cupric (Cu+2) to cuprous (Cu+1) upon simultaneous oxidation to disulfides in the membrane. Cuprous ions are reoxidized to Cu+2 in the presence of molecular oxygen molecular oxygen is thereby converted to the toxic superoxide radical O2, which induces lipoperoxidation (Aaseth and Norseth 1986). 

An ECD measures the current generated by electroactive analytes in the HPLC eluent between electrodes in the flow cell. It offers sensitive detection (pg levels) of catecholamines, neurotransmitters, sugars, glycoproteins, and compounds containing phenolic, hydroxyl, amino, diazo, or nitro functional groups. The detector can be the amperometric, pulsed-amperometric, or coulometric type, with the electrodes made from vitreous or glassy carbon, silver, gold, or platinum, operated in the oxidative or reductive mode. Manufacturers include BSA, ESA, and Shimadzu. 

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