Dopamine 3-hydroxylase copper

Copper is one of the twenty-seven elements known to be essential to humans (69—72) (see Mineral nutrients). The daily recommended requirement for humans is 2.5—5.0 mg (73). Copper is probably second only to iron as an oxidation catalyst and oxygen carrier in humans (74). It is present in many proteins, such as hemocyanin [9013-32-3] galactose oxidase [9028-79-9] ceruloplasmin [9031 -37-2] dopamine -hydroxylase, monoamine oxidase [9001-66-5] superoxide dismutase [9054-89-17, and phenolase (75,76). Copper aids in photosynthesis and other oxidative processes in plants. 

Dopamine hydroxylase belongs to the copper-dependent monooxygenases and is important in the control of the neurotransmitter concentrations of dopamine and norepinephrine [59]. 

Dopamine -hydroxylase is a copper-containing enzyme involved in the synthesis of the catecholamines noradrenaline and adrenaline from tyrosine in the adrenal medulla and central nervous system (see Figure 13.4). The active enzyme contains Cu+, which is oxidized to Cu + during the hydroxylation of the substrate. Reduction back to Cu+ specifically requires ascorbate, which is oxidized to monodehydroascorbate. 

Ascorbic acid has specific and well-defined roles in two classes of enzymes the copper-containing hydroxylases (such as dopamine -hydroxylase and peptidyl glycine hydroxylase) and the 2-oxoglutarate-Unked iron-containing hydroxylases, of which the best studied are the proUne and lysine hydroxylases involved in maturation of connective tissue (and other) proteins. 

The clinical symptoms of classical Menkes disease can be traced back to developmentaUy important copper enzymes such as lysyl oxidase, tyrosinase (see Copper Hemocyanin/Tyrosinase Models), cytochrome c oxidase (see Cytochrome Oxidase), dopamine -hydroxylase, superoxide dismutase, and amine oxidase (see Superoxide Dismutase). Lysyl oxidase is needed for the cross-linking of connective tissue a deficiency in this enzyme causes weakened connective tissue and connective tissue disorder such as arterial ruptures as observed in these patients. Low levels of cytochrome c oxidase cause temperature instability and the absence of tyrosinase explains the hair depigmentation observed in affected individuals. ... 

A number of copper requiring enzymes are located at the cell surface or are exported into the extracellular milieu. Examples of such secretory Cu-enzymes include copper requiring ferroxidases that fimction in iron transport (e g. ceruloplasmin, CP), enzymes for neurotransmission (peptidyl amidating enzyme and dopamine hydroxylase), an extracellular superoxide dismutase (SOD) that fimctions in antioxidant defense and enzymes for formation of connective tissue (lysyl oxidase), and pigments (tyrosinase) (reviewed in ). En route to their designated location, each of these enzymes passes through a specialized compartment of the late Golgi where copper insertion takes place. 

Tyrosine monooxygenase uses biopterin as a cofactor. Biopterin is made in the body and is not a vitamin. Its structure resembles that of folic acid. Dopa decarboxylase is a vitamin B -requiring enzyme. Dopamine hydroxylase is a copper metalloenzyme. The active form of the enzyme contains copper in the reduced state (cuprous, Cu+). With each catalytic event, the copper is oxidized to the cupric state (Cu ). The enzyme uses ascorbic acid as a cofactor for converting the cupric copper back to cuprous copper. Thus, each catalytic event also results in the conversion of ascorbic acid to semidehydroascorbate. The semidehydroascorbate, perhaps by disproportionation, is converted to ascorbate and dehydroascorbate. The catalytic cycle of dopamine hydroxylase is shown in Figure 9,86. Dopamine hydroxylase, as well as the stored catecholamines, are located in special vesicles... 

Dopamine- -hydroxylase is another copper enzyme that plays a major function in the biosynthesis of norepinephrine (40). A protective catalyst, superoxide dismutase, has been described to catalyze the dismu-tation of the superoxide anion free radical (41). Other enzymes known to contain copper are the laccases, the phenol oxidases, and the ascorbic acid oxidases (12). 

Two possible mechanisms for the neurotoxicity of carbon disulfide have been suggested. One mechanism involves the formation of dithiocarbamates. The inhibitory effect of carbon disulfide on the activity of the copper-requiring enzyme dopamine- -hydroxylase was attributed to the formation of dithiocarbamates, which can complex copper (McKenna and DiStefano 1977b). Interference with the formation of this metabolite may be a potential strategy, albeit untested, to reduce neurotoxicity from carbon disulfide poisoning. An alternative mechanism postulated to explain the neurotoxic effect of carbon disulfide is the formation of a dithiocarbamate derivative, a form of vitamin B6, of pyridoxamine, with carbon disulfide (Vasak and Kopecky 1967). Since transaminases and amine oxidases require the pyridoxamine phosphate form of vitamin B6 as a cofactor, it was further postulated that these enzymes would be inhibited in carbon... 

Fig. 24. Oxidized and reduced state of the dopamine /1-hydroxylase copper center. The reducing agent is ascorbate. From Pettingill et al. 1991 [31] with permission...

Copper is an essential trace metal which is a component of a wide range of intracellular metalloen/ymes. including cytochrome oxidase, superoxide dismutase. tyrosinase, dopamine hydroxylase and lysyl oxidase. Most of the copper in plasma is associated w-ith the specific copper-binding protein, caeruloplasmin. 

Dopamine -hydroxylase has been obtained in essentially pure form from bovine adrenal glands (4). It has a molecular weight of approximately 290,000. Although the protein is colorless, metal analysis showed that it is a copper protein containing between 0.65 and 1.0 /xgram of copper per mg. of protein (4-7 moles of copper/mole protein). Part of the copper is present as Cu and part as Cu. Although the amount of Cu varies from one enzyme preparation to another, the amount of Cu is relatively constant and is equal to about two moles per mole of enzyme. 

Copper is an essential trace element for humans and other animals. Copper ions are included in the active centres of many enzymes, especially cytochrome c oxidase, superoxide dismutase, various aminoxidases (such as lysyl oxidase), hydroxylases (e.g. dopamine -hydroxylase and tyrosinase), galactose oxidase or different phenoloxidases, such as laccase and other oxidoreductases. The so-called blue copper proteins, for example plastocyanin, azurin and plantacyanin, occur in many prokaryotic organisms and plants. These proteins, by a change to the bound copper valency, provide electron transfer in various redox processes. 

The final stage in the biosynthesis of NA involves a second mixed function oxidase, dopamine- -hydroxylase. This enzyme has been extensively purified from the bovine adrenal medulla, and is a copper-containing protein of molecular weight 290,000. Ascorbic acid acts as the cofactor (XHj). Enzyme activity is stimulated by catalytic amounts of fumaric acid and by certain other dicarboxylic acids. The enzyme has a broad substrate specificity, and will catalyse the /7-hydroxylation of a large number of phenylethylamine derivatives, including a number of sympathomimetic amines (Table 8). 

In addition to its antioxidant role, ascorbic acid functions to keep various metallic ions in catalytic centers in their reduced forms. For example, some oxygenases require iron or copper in their Fe + or Cu+ states of oxidation. If these protein-bound ions are accidentally left in a more oxidized state they may need to be reduced by ascorbate ions. While this is a protectant role, there are some enzymes for which ascorbate has become a cosubstrate. An example is dopamine -hydroxylase, which converts dopamine to the neurotransmitter noradrenaline. The enzyme contains copper which cycles between Cu+ and Cu +, as it incorporates one atom of oxygen from O2 into its substrate. Ascorbate supplies the electrons for reduction of the second atom of the O2 to H2O. A recent report describes another distinct function for ascorbate ion. It apparently acts as a basic catalytic group for proton abstraction from a water molecule during the action of a glycosyltransferase enzyme, becoming part of the active site of that enzyme. 

Dodecametallic complexes, 1,167 Dodecamolybdometalates, 3,1045 Dodecatantalates, 3,1029 Dolerophane, 6,855 Donor numbers, 2,74 Dopamine (3-hydroxylase, 6, 711 copper, 6,654... 

Dopamine /3-hydroxylase (D/3H) is a copper-containing glycoprotein that hydroxylates dopamine at the benzylic position to norepinephrine.84 During the attempted crystallization of the bis(hydroxide)-bridged dicopper(II) dimer, a side product was subsequently isolated (complex (63)), revealing intramolecular hydroxylation at a formally benzylic position of the tris(imidazo-lyl)phosphine ligand.85 The copper(II) center has an axially compressed TBP structure. 

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). 

Dopastin is an experimental antihypertensive agent which has been noted to potently inhibit copper-dependent dopamine p hydroxylase [100]. The pharmacological... 

Copper is a component of many enzymes including amine oxidase, lysyl oxidase, ferroxidase, cytochrome oxidase, dopamine P-hydroxylase, superoxide dismutase and tyrosinase. This latter enzyme is present in melanocytes and is important in formation of melanin controlling the colour of skin, hair and eyes. Deficiency of tyrosinase in skin leads to albinism. Cu " ion plays an important role in collagen formation. 

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). 

Transition metal hydroperoxo species are well established as important intermediates in the oxidation of hydrocarbons (8,70,71). As they relate to the active oxygenating reagent in cytochrome P-450 monooxygenase, (porphyrin)M-OOR complexes have come under recent scmtiny because of their importance in the process of (poiphyrin)M=0 formation via 0-0 cleavage processes (72-74). In copper biochemistry, a hydroperoxo copper species has been hypothesized as an important intermediate in the catalytic reaction of the copper monooxygenase, dopamine P-hydroxylase (75,76). A Cu-OOH moiety has also been proposed to be involved in the disproportionation of superoxide mediated by the copper-zinc superoxide dismutase (77-78). Thus, model Cun-OOR complexes may be of... 

This enzyme [EC 1.14.17.1], also known as dopamine j8-hydroxylase, is a copper-dependent system catalyzing the reaction of 3,4-dihydroxyphenethylamine with ascorbate and dioxygen to produce noradrenaline, dehydroascorbate, and water. The enzyme is stimulated by fu-marate. 

These systems are also described as normal copper proteins due to their conventional ESR features. In the oxidized state, their color is light blue (almost undetectable) due to weak d-d transitions of the single Cu ion. The coordination sphere around Cu, which has either square planar or distorted tetrahedral geometry, contains four ligands with N and/or 0 donor atoms [ 12, 22]. Representative examples of proteins with this active site structure (see Fig. 1) and their respective catalytic function include galactose oxidase (1) (oxidation of primary alcohols) [23,24], phenylalanine hydroxylase (hydroxy-lation of aromatic substrates) [25,26], dopamine- 6-hydroxylase (C-Hbond activation of benzylic substrates) [27] and CuZn superoxide dismutase (disproportionation of 02 superoxide anion) [28,29]. 

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