Dopa, dopamine

Adrenaline, Noradrenaline, Dopamine, Dopa as Triacetyl Derivatives [6]... 

The effect of non-participating ligands on the copper catalyzed autoxidation of cysteine was studied in the presence of glycylglycine-phosphate and catecholamines, (2-R-)H2C, (epinephrine, R = CH(OH)-CH2-NHCH3 norepinephrine, R = CH(OH)-CH2-NH2 dopamine, R = CH2-CH2-NH2 dopa, R = CH2-CH(COOH)-NH2) by Hanaki and co-workers (68,69). Typically, these reactions followed Michaelis-Menten kinetics and the autoxidation rate displayed a bell-shaped curve as a function of pH. The catecholamines had no kinetic effects under anaerobic conditions, but catalyzed the autoxidation of cysteine in the following order of efficiency epinephrine = norepinephrine > dopamine > dopa. The concentration and pH dependencies of the reaction rate were interpreted by assuming that the redox active species is the [L Cun(RS-)] ternary complex which is formed in a very fast reaction between CunL and cysteine. Thus, the autoxidation occurs at maximum rate when the conditions are optimal for the formation of this species. At relatively low pH, the ternary complex does not form in sufficient concentration. 

Figure 1-1 shows an example of the detection limits that can be reached with EC detection. The chromatogram shows the separation and detection of the catecholamines noradrenaline (nor), adrenaline (adr), dihydroxybenzylamine (dhba), and dopamine (dopa), using a glassy carbon electrode at a working potential of +0.6 V. The minimum detectable quantity is less than 3 Pg-... 

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... 

DA = dopamine DOPA = dihydroxyphenylalanine MHPG = 3-methoxy-4-hydroxyphenylglycol. 

Steps in the formation of classical neurotransmitters. AADC, amino acid decarboxylase AChE, acetylcholinesterase CAT, choline acetyltransferase COMT, catechol-O-methyltransfeiase DBH, dopamine P-hydroxylase DA, dopamine DOPA, dibydroxyphenylalanine GABA-T, GABA transaminase GAD, glutamic acid decarboxylase HD, histidine decarboxylase 5-HTP, 5-hydroxytrytophan MAO, monoamine oxidase PNMT, phenylethanolamine N-methyltransferase TH, tyrosine hydroxylase TPH, tryptophan hydroxylase. 

Specific decarboxylases are known for a majority of the amino acids, and several are prime targets for inactivation by virtue of their substantial medicinal importance. These include aromatic-amino-acid decarboxylase, which is responsible for the production of dopamine (DOPA) orithine decarboxylase, which supplies the p amine putrescine and glutamate decarboxylase, which converts glutamate to the inhibitory neurotransmitter y-aminobutyric acid (GABA). The accepted mechanism of these enzymes involves decarboxylation of the amino acid to yield a resonance-stabilized carbanion at the a-carbon of the substrate. The intermediate is then protonated with retention of configuration to yield product (Walsh, 1979, p. 800). 

L-dopa is a chemical intermediate produced in the synthesis of dopamine (see Figure below). It is formed from the actions of tyrosine hydroxylase on tyrosine, and is subsequently converted into dopamine by aromatic-L-amino acid decarboxylase (LAAD, or dopa decarboxylase). This molecule is taken up into the dopaminergic nerve terminal and converted to dopamine, which is then released into the synaptic cleft. Unlike dopamine, dopa is in nonionized form at physiologic pH and thus will cross into the central nervous system (CNS). 

No cross-reactivity has been seen with other nitro aromatics, such as nitro-phenylalanine, nitrotryptophan, or nitroguanine, nor with physiological tyrosine analogs such as phosphostyrosine, chlorotyrosine, dopamine, DOPA, dopamine, or tyramine (Ye et al., 1995). 

Dopamine Dopa Norepinefrine, epinefrine Mediators of sympathetic nerves... 

Fig. 17.2 Structures of the monoamine neurotransmitters and trace monoamines tested as the corresponding hydrochlorides 2-phenylethylamine (PEA), tyramine (Tyrm), dopamine (Dopa), serotonm (Sert), y-aminobutyric acid (GABA), histamine (Hist) and norepinephrine (Nore)...

Stassen et al. [1026] described an interesting application for a supported CP membrane constructed by electrodepositing a 1 to 6 ixm thick film of poly(3-hexyl-thiophene) onto a thin (20 nm) Au layer deposited in turn on a Millipore Durapore membrane (average pore size 0.1 /im), i.e. the final configuration was CP/Au/-Durapore. They then mounted this membrane in a test cell and measured the permeability of the neurotransmitter dopamine (Dopa) through it as a function of potential applied to the membrane. They however found a poor variation of the permeation rate, only of the order of 40%. Response time for observable permeation was also poor, being of the order of hours. 

A, adrenaline COMT, catechol-O-methyl transferase CSF, cerebrospinal fluid DA, 3,4-dihydroxyphenylethylamine (dopamine) Dopa, 3,4-dihydroxyphenylalanine 5HIAA, 5-hydroxyindoleacetic acid 5HT, 5-hydroxytryptamine (serotonin) 5HTP, 5-hydroxytryptophan HVA, 3-methoxy-4-hydroxyphenylacetic acid (homovanillic acid) MAO, monoamine oxidase MAOI, monoamine oxidase inhibitor MHPG,... 

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