Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.10.3.1 (tyrosinase)
9,065 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

4-Methyl catechol and catechol, at concentrations ranging from 0.03 to 9 mM and 0.066 to 20 mM, respectively, have a synergistic effect on the rate of DL-DOPA oxidation by mushroom tyrosinase to material absorbing at 475 nm. The synergism results from the ability of 4-methyl catechol-o-quinone (4-methyl-o-benzoquinone) and of catechol-o-quinone (o-benzoquinone) to oxidize DL-DOPA non-enzymatically to dopaquinone, with the later being immediately converted to dopachrome (lambda max = 475 nm).
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PMID:Synergism exerted by 4-methyl catechol, catechol, and their respective quinones on the rate of DL-DOPA oxidation by mushroom tyrosinase. 163 Oct 21

Dihydroxybenzoic acids (DBA), such as 3,4-DBA, 3,5-DBA, and 2,4-DBA--at all concentrations tested--inhibited the rate of DL-DOPA oxidation to dopachrome (lambda max = 475 nm) by mushroom tyro0sinase. 2,3-DBA and 2,5-DBA at relatively low concentration had a synergistic effect on the reaction, whereas at relatively high concentrations they inhibited the rate of DL-DOPA oxidation. The synergistic effect of 0.6-13.3 mM 2,3-DBA on the rate of DL-DOPA oxidation to dopachrome (lambda max = 475 nm) was found to be due to the ability of 2,3-DBA-o-quinone (formed by the oxidation of 2,3-DBA by mushroom tyrosinase or by sodium periodate) to oxidize DL-DOPA to dopachrome (via dopaquinone) non-enzymatically. A similar explanation is likely to be valid for the synergism exerted by 2,5-DBA on the rate of DL-DOPA oxidation by mushroom tyrosinase.
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PMID:Effect of different isomers of dihydroxybenzoic acids (DBA) on the rate of DL-dopa oxidation by mushroom tyrosinase. 163 Oct 23

Two pigmentation related genes have recently been cloned which map to the brown (b) and albino (c) loci of mice; these loci influence the quality and quantity, respectively, of melanin produced by melanocytes. Both these gene products are biochemically similar and have extensive amino acid sequence similarity to each other and to lower forms of tyrosinase (EC 1.14.18.1), a copper binding enzyme responsible for melanin production. In order to characterize the catalytic activities of these molecules, we have synthesized peptides and prepared antibodies to them which specifically recognize the gene products in question. By use of immune affinity purification protocols, we have isolated the proteins encoded by the brown and albino loci and have determined that both have the catalytic functions ascribed to tyrosinase, i.e. hydroxylation of tyrosine to 3,4-dihydroxyphenylalanine (DOPA) and the oxidation of DOPA to DOPAquinone. These are the critical reactions to melanogenesis since melanin pigment can be spontaneously produced from those products. The specific activity of the albino locus encoded product is considerably higher than that of the protein encoded by the brown locus, although the latter protein is present in higher quantity in melanocytes than is the protein encoded by the albino locus. These results are surprising since it was anticipated that tyrosinase was the product of single gene locus, and suggest that regulation of melanogenesis in mammals is controlled at the enzymatic level by several different gene products.
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PMID:Tyrosinases from two different loci are expressed by normal and by transformed melanocytes. 189 30

The early enzyme-mediated reaction sequence in the biosynthesis of melanin from L-tyrosine involves an initial hydroxylation (monophenol oxidase activity, MPO) of the aromatic amino acid precursor to form L-dopa (3,4-dihydroxyphenylalanine), and the ensuing oxidation (diphenol oxidase activity, DPO) of the resultant diphenol to form dopaquinone. By means of high pressure liquid chromatography with electrochemical detection (HPLC-ED) both phenol oxidase activities were observed in the blood (hemolymph) of two species of insect, third-stage larvae of Drosophila melanogaster and adult Locusta migratoria, and in an adult fresh-water crayfish, Austropotamobius pallipes. These results establish that in each species MPO and DPO can be detected readily without the use of exogenous activators.
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PMID:Hemolymph phenol oxidases in Drosophila melanogaster, Locusta migratoria, and Austropotamobius pallipes. 195 49

Phosphonic acid and phosphinic acid analogues of tyrosine and 3,4-dihydroxyphenylalanine (dopa) were found to influence tyrosinase activity, thus being potential regulators of melanization in mammalian cells. The analogues were tested for their cytostatic activity in vitro, by means of total cell protein determination, on mouse B16 melanoma and, for comparison, on human KB carcinoma cell lines. Four compounds out of 22 revealed promising cytostatic activity for both cell lines, being nearly equipotent with dopa. Those compounds which most effectively suppressed the growth of both tumour cell lines were the same as those which had a significant influence on tyrosinase activity regardless of whether they acted as inhibitors or substrates.
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PMID:Phosphonic and phosphinic acid analogues of tyrosine and 3,4-dihydroxyphenylalanine (dopa) as potential antimelanotic agents. 212 80

The catechol oxidase-catalysed and autoxidative transformation of 3,4-dihydroxyphenylalanine (DOPA) to eumelanin have been studied by oxygen consumption, energy transfer, absorption and fluorescence spectroscopy. Formation of transient dopachrome (lambda max = 480 nm) and dopalutin (lambda ex = 423 nm, lambda em = 491 nm) have been found in the enzymatic and autoxidative reaction. In the enzymatic reaction, neither a photon emission with quantum yield phi greater than 10(-13) nor energy transfer to triplet and singlet energy acceptors (sensitizers such as anthracene derivatives, xanthene dyes and chlorophyll-a) in water and micellar solutions have been found. The autoxidative reaction is chemiluminescent (phi = 10(-9)), the emission occurring in the 400-600 nm range. The excitation energy is not transferred to sensitizers. The effect of various enzymes and traps of active oxygen species as well as the spectral distribution of chemiluminescence indicate that there is no emission from oxygen dimoles. Carbonates and active species of oxygen are shown to participate in the chemiexcitation reaction.
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PMID:Studies on chemiluminescence in the enzymatic and autoxidative transformation of 3,4-dihydroxyphenylalanine into eumelanins. 250 33

Several diseases are included in the category of hypomelanosis. Their clinical course as well as the pathogenesis are diverse and in many cases poorly understood. The aim of the present study is to use the nude mice model to determine whether the primary defect in various pigmentary skin disorders is inherent to the tissue itself or is secondary to systemic factors. Split-thickness skin grafts obtained from patients with vitiligo, acquired hypomelanosis guttata, and tyrosinase-negative albinism were grafted onto nude mice. Histologic examination and dopa staining were performed prior to and following the engraftment. The dopa staining was performed on the epidermal sheet following separation from the dermis. The depigmented area of the vitiligo became completely pigmented 6 to 10 weeks after skin transplantation. The dopa reaction that was negative prior to skin engraftment became completely positive after the transplantation. The number of melanocytes (expressed per square millimeter of skin surface) 8 weeks after transplantation was 197 +/- 73 mm2. Dopa reaction in acquired hypomelanosis guttata showed reduction of the number of melanocytes in the depigmented macula as compared with the surrounding area (55.25 +/- 18.00 mm2 vs 220 +/- 28.28 mm2. Twenty days after skin transplantation, repigmentation of the area was observed. The number of melanocytes increased significantly (388.75 +/- 213 mm2). The grafted skin obtained from patients with tyrosinase-negative albinism showed persistence of the depigmentation after skin transplantation. Dopa reaction was negative prior to and 8 weeks after transplantation. The results of the present study suggest that systemic factors may play a role in the pathogenesis of vitiligo and acquired hypomelanosis guttata.
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PMID:Vitiligo and idiopathic guttate hypomelanosis. Repigmentation of skin following engraftment onto nude mice. 236 61

L-dopa is a key metabolite in the process of melanogenesis. However, it is difficult to use in biological experiments because it is subject to auto-oxidation and relatively insoluble at neutral pH. Dopa phosphates contain phosphate ester linkages at positions 3 and/or 4 of the phenylalanine ring of L-dopa, rendering them highly soluble and stable to auto-oxidation when compared to L-dopa. Dopa phosphates are readily taken up by melanoma cells in culture and converted to L-dopa and inorganic phosphate by cellular phosphatases, making them useful for studying L-dopa effects in vivo. Here we investigated the effects of dopa phosphates on receptors for MSH in cultured melanoma cells. We found that dopa phosphates caused a 3-fold stimulation of MSH binding capacity by the cells which probably occurred through an increase in the number of receptors for MSH with no apparent change in affinity of the receptors. The increased binding capacity for MSH was followed by increased cellular tyrosinase activity and melanogenesis. Thus dopa phosphates and/or L-dopa can act as regulators of the MSH receptor system. The observations suggest a novel mechanism for regulation of hormonal responsiveness: hormonal signal amplification by a metabolite in the target pathway.
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PMID:Phosphorylated isomers of L-dopa stimulate MSH binding capacity and responsiveness to MSH in cultured melanoma cells. 288 96

The toxicity and selectivity of 3,4-dihydroxybenzylamine (DHBA), an experimental antimelanoma agent that cannot enter the melanin pathway, broadly paralleled that of L-dopa in a panel of human melanoma cell lines sensitive or resistant to the latter drug. A human retinoblastoma cell line was found to be sensitive to both compounds. The toxicity and selectivity of both catechols were associated with inhibition of DNA synthesis; DHBA was more potent yet allowed a much greater degree of recovery compared with an equitoxic level of dopa. Dopa and DHBA had similar, dose-dependent effects on the cell cycle, arresting cells in S phase at low doses and in G1 at high doses. Replication of the DNA virus adenovirus was found to be inhibited by both agents. There was no difference between sensitive and resistant cell lines in the manganese or copper/zinc forms of superoxide dismutase, or in iron content and iron-binding capacity. Catechol toxicity was inhibited by the hydrogen peroxide scavenging agents pyruvate and methaemoglobin. Sensitivity to catechols did not correlate with melanin or tyrosinase content, rate of incorporation of tyrosine or dopa, intracellular levels of phenylalanine or tyrosine, or binding of a new monoclonal antibody directed against a melanosomal protein. These results indicate that DHBA and dopa exhibit selective toxicity for neural crest tumor cells independently of the melanisation pathway and of the superoxide scavenging system.
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PMID:Melanin synthesis and the action of L-dopa and 3,4-dihydroxybenzylamine in human melanoma cells. 290 84

The cytotoxicity of catechols has been ascribed to covalent binding of the omicron-quinone oxidation products to proteins through sulfhydryl groups. The nature of the covalent binding was studied with dopaquinone formed on tyrosinase oxidation of 3,4-dihydroxyphenylalanine (DOPA). After acid hydrolysis of the reaction products, cysteinyldopas liberated (protein-bound cysteinyldopas) were determined by HPLC with electrochemical detection. When 0.1 mM DOPA was oxidized in the presence of 0.2 mM bovine serum albumin, alcohol dehydrogenase or isocitrate dehydrogenase, protein-bound cysteinyldopas were formed in yields of 5.4, 44, or 33%, respectively. The covalent binding was almost completely inhibited by 1 mM cysteine or 1 mM ascorbic acid, but 10 mM lysine had no effect. These results unambiguously demonstrate that dopaquinone can bind with proteins mostly through sulfhydryl groups.
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PMID:Tyrosinase-catalyzed binding of 3,4-dihydroxyphenylalanine with proteins through the sulfhydryl group. 293 36


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