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)

Nuclear extracts from the uteri of estradiol-implanted rats contain a tyrosinase-like enzyme that has three activities: monophenolase or cresolase, diphenolase or catecholase, and estrogen binding. When [3H]estradiol was used as a substrate, 3H2O was released from the A ring in the presence of copper and ascorbic acid. The optimal concentrations of these cofactors for the cresolase activity were established. The cresolase activity was lost on attempts at further purification. Estradiol binding was observed in conjunction with the enzymatic activity and was dependent on the presence of ascorbic acid and copper. The most potent inhibitors of 3H2O release from [3H]estradiol were those with a dihydroxyphenol moiety. The reaction was also sensitive to sulfhydryl reagents. These features of the enzyme are distinctive from other oxidases capable of attacking the aromatic ring of estrogens.
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PMID:Tyrosinase-like activity and estradiol binding in rat uterine nuclear extracts. 148 87

Nuclear and cytosolic fractions of rat uteri and tissues from the central nervous system contain proteins that are recognized by a polyclonal tyrosinase antibody. This antibody eliminates the cresolase activity of uterine nuclear extract when estradiol is used as substrate. Thus, it appears that tyrosinase-like proteins might be present in tissues not generally considered to chain such an enzyme.
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PMID:Tyrosinase-like polypeptides in the uterus and in the central nervous system of rats. 151 62

1. The liver pigment cells of R. esculenta L. constitute a peculiar pigment cell system of histiocytic nature and contain a tyrosinase-like activity localized in the protein component of melanosomes. 2. The effects of addition and/or removal of Cu on the DOPA-oxidase activity of the system were studied. 3. It was concluded that: (a) this tyrosinase behaves as a Cu-enzyme; (b) Cu could be involved in the regulation of the enzyme activity; and (c) mixtures of apoenzyme and active enzyme coexist in the melanosomes.
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PMID:Effects of copper on the tyrosinase of liver pigment cells from Rana esculenta L. 211 47

Three albino mutants of the fowl were tested for tyrosinase activity. Two of these mutants (c and ca) are alleles at the autosomal C locus, while the third mutant (sal) is sex-linked. Both the standard type, E, and sal are tyrosinase positive whereas the two C mutants are tyrosinase negative. Anti-chicken tyrosinase mouse serum was produced and all four genotypes were found to have cross-reacting material to this antiserum. Tyrosinase from the standard type was isolated and its location on denaturing two-dimensional gels determined. A co-migrating series of spots was found within the protein pattern of both the standard type and the tyrosinase positive albino, sal. The same pattern of spots was also observed for c and ca with no apparent change in either the pI or the molecular weight. Transmembrane blots also showed spots that reacted with anti-tyrosinase serum in all four genotypes and that migrated to the same location as that of standard tyrosinase. It is proposed that both c and ca are CRM+ mutants which produce tyrosinase-like molecules that are inactive due to a change that is electrophoretically and antigenically "silent".
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PMID:C pigment locus mutants of the fowl produce enzymatically inactive tyrosinase-like molecules. 393 85

A tyrosinase-like activity was found in human substantia nigra by polyacrylamide gel electrophoresis of fractions prepared from homogenates of the substantia nigra. The enzyme activity was detected by staining the gels with L-3,4-dihydroxyphenylalanine, dopamine and 5,6-dihydroxyindole as substrates for tyrosinase (EC 1.14.18.1). A case of parkinsonism does not show the L-3,4-dihydroxyphenylalanine and dopamine oxidase activities.
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PMID:Tyrosinase-like activity in normal human substantia nigra. 644 36

We have previously described tyrosinase-like proteins of rat uterine nuclear extracts with type II estrogen binding characteristics. In this paper we have been able to affinity label these polypeptides with radio-iodinated estradiol. The major label at approximately 33-38 kDa comigrates with a approximately 36 kDa tyrosinase immunoreactive band assessed by autoradiograms and Western blots following electrophoresis. A minor label was also detected at approximately 45 kDa. The label is attenuated by excess quercetin hence these proteins are believed to represent putative type II estrogen binding sites that bind this bioflavonoid. These estrogen binding proteins are distinct from the estrogen receptor as judged by immunoblotting. The affinity crosslinking will be a useful approach in the purification of tyrosinase like proteins.
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PMID:Estrogen affinity crosslinking to tyrosinase-like immunoreactive proteins of rat uterine nuclear extracts. 803 12

Dipteran arylphorin receptors, insect hexamerins, cheliceratan and crustacean hemocyanins, and crustacean and insect tyrosinases display significant sequence similarities. We have undertaken a systematic comparison of primary and secondary structures of these proteins. On the basis of multiple sequence alignments the phylogeny of these proteins was investigated. Hexamerin subunits, hemocyanin subunits, and tyrosinases share extensive similarities throughout the entire amino acid sequence. Our studies suggest the origin of arthropod hemocyanins from ancient tyrosinase-like proteins. Insect hexamerins likely evolved from hemocyanins of ancient crustaceans, supporting the proposed sister-group position of these subphyla. Arylphorin receptors, responsible for incorporation of hexamerins into the larval fat body of diptera, are related to hexamerins, hemocyanins, and tyrosinase. The receptor sequences display extensive similarities to the first and third domains of hemocyanins and hexamerins. In the middle region only limited amino acid conservation was observed. Elements important for hexamer formation are deleted in the receptors. Phylogenetic analysis indicated that dipteran arylphorin receptors diverged from ancient hexamerins, probably early in insect evolution.
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PMID:Common origin of arthropod tyrosinase, arthropod hemocyanin, insect hexamerin, and dipteran arylphorin receptor. 866 23

Dopamine acts, under appropriate conditions, as a selective neurotoxin. This toxicity is attributed to the autoxidation of the neurotransmitter into a reactive quinone that covalently modifies cellular macromolecules (i.e. proteins and nucleic acids). The oxidation of the catecholamine to a quinone is greatly accelerated by the enzyme tyrosinase. There is controversy, however, as to whether or not tyrosinase is expressed in human brain. In the present study, RT-PCR was utilized to demonstrate the presence of tyrosinase mRNA in post-mortem human brain tissues. Using gene-specific amplification primers, specific tyrosinase amplicons were detected following analysis of RNA from substantia nigra of four individuals. Analysis of cerebellar RNA from the same individuals produced no amplification products. Control reactions performed in the absence of reverse transcriptase failed to generate PCR products for any tissue tested. Three amplicons were subjected to direct DNA sequencing and all proved to be identical with tyrosinase sequences, thus obviating the possibility of amplification of a related gene. It is clear, therefore, that the tyrosinase gene is expressed in the human substantia nigra, lending support to previous studies describing tyrosinase-like activity and immunoreactive protein in the brain. This enzyme could be central to dopamine neurotoxicity as well as contribute to the neurodegeneration associated with Parkinson's disease.
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PMID:Tyrosinase mRNA is expressed in human substantia nigra. 910 85

Hemocyanin and tyrosinase are dinuclear copper proteins capable of reversibly binding dioxygen. Despite the great similarity of structure and properties of their active site, the two proteins perform different biological functions (oxygen transport/storage versus monooxygenase and oxidase activity). In this paper, we show that Octopus vulgaris hemocyanin exhibits a tyrosinase-like activity; namely, it is capable of utilizing dioxygen for the oxidation of o-diphenol to quinone. The reaction is specific for this isomer of diphenol, the meta and para isomers being unreactive, and is strongly controlled by steric factors. Dioxygen represents a cosubstrate of the reaction, and it is involved in the catalytic turnover by binding to the dinuclear copper site of the protein to form, under steady-state conditions, oxy-Hc, which is the active species. The generation of semiquinone radicals, detected by EPR and by their reaction with N,N,N',N'-tetramethyl-1,4-phenylenediamine, strongly supports a reaction mechanism in which such radicals represent the reaction products of one-electron oxidation of the substrate, quinone being generated by dismutation of semiquinones. Met-Hc is regenerated by the substrate to the deoxy form. To close the catalytic cycle, the proposed reaction mechanism also involves the participation of two transient protein forms with the total oxidation state of the active site (V and IV) intermediate between that of oxy-Hcy, [CuIIO22-CuII]VI, and deoxy-Hc, [CuICuI]II. A mathematical model has been elaborated to describe the reaction kinetics. The differences in reaction mechanisms between hemocyanin and tyrosinase are discussed in terms of accessibility to exogenous molecules of their active sites.
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PMID:The enzymatic properties of Octopus vulgaris hemocyanin: o-diphenol oxidase activity. 976 Feb 42

Marinomonas mediterranea is a recently isolated melanogenic marine bacterium containing laccase and tyrosinase activities. These activities are due to the expression of two polyphenol oxidases (PPOs), a blue multicopper laccase and an SDS-activated tyrosinase. The gene encoding the first one, herein denominated M. mediterranea PpoA, has been isolated by transposon mutagenesis, cloned and expressed in Escherichia coli. Its predicted amino acid sequence shows the existence of a signal peptide and four copper-binding sites characteristic of the blue multicopper proteins, including all fungal laccases. In addition, two additional putative copper-binding sites near its N-terminus are also present. Recombinant expression in E. coli of this protein clearly demonstrates its multipotent capability, showing both laccase-like and tyrosinase-like activities. This is the first prokaryotic laccase sequenced and the first PPO showing such multipotent catalytic activity. The expression of several truncated products indicates that the four copper-binding sites typical of blue multicopper proteins are essential for the laccase activity of this enzyme. However, the last two of these sites are not necessary for tyrosine hydroxylase activity as this activity is retained in a truncated product containing the first two sites as well as the extra histidine-rich clusters close to the N-terminus of the protein.
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PMID:Molecular cloning and functional characterization of a unique multipotent polyphenol oxidase from Marinomonas mediterranea. 1134 96


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