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)

Agaritine (N2-[L-(+)-glutamyl]-4-(hydroxymethylphenyl)hydrazine), the principal hydrazine found in the edible mushroom Agaricus bisporus, as well as the N'-acetyl derivative of 4-(hydroxymethyl)phenylhydrazine and 4-(hydroxymethyl)benzene diazonium ion, as the tetraborate salt, considered as the putative proximate and ultimate carcinogens of agaritine, were all synthesised chemically. The mutagenicity of these compounds and of 4-hydrazinobenzoic acid, a precursor of agaritine biosynthesis in mushroom, was investigated in the Ames test, using Salmonella typhimurium strain TA104, in the absence and in the presence of either mushroom tyrosinase or rat hepatic cytosol as activation systems. In the absence of an activation system the diazonium ion was clearly the most mutagenic of the four compounds studied. When tyrosinase was used as activation system, the mutagenicity of N'-acetyl-4-(hydroxymethyl)phenylhydrazine was enhanced; glutathione and superoxide dismutase markedly suppressed the mutagenic response. When the mutagenicity of the four compounds was evaluated in the presence of rat hepatic cytosol, an increase was seen only in the case of N'-acetyl-4-(hydroxymethyl)phenylhydrazine; this was shown to be due to deacetylation releasing the more mutagenic free hydrazine. Collectively, the above data are compatible with an activation of agaritine that involves an initial loss of the gamma-glutamyl group followed by microsomal oxidation of the free hydrazine to generate the diazonium ion. Also of interest is the observation that mushroom tyrosinase can convert N'-acetyl-4-(hydroxymethyl)phenylhydrazine to mutagenic product(s); whether these products contribute to the mutagenicity of mushroom extracts remains to be established.
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PMID:Bioactivation of mushroom hydrazines to mutagenic products by mammalian and fungal enzymes. 940 39

The inactivation of the catecholase activity of mushroom tyrosinase was investigated under nonaqueous conditions. The enzyme was immobilized on glass beads, and assays were conducted in chloroform, toluene, amyl acetate, isopropyl ether, and butanol. The reaction components were pre-equilibrated for 2 weeks with a saturated salt solution at a water activity of 0.90. The initial reaction velocity varied between 1.3 x 10(3) mol product/((mol enzyme)(min)) in toluene and 8.7 x 10(3) mol product/((mol enzyme)(min)) in amyl acetate. The turnover number varied between 8.1 x 10(3) mol product/mol enzyme in toluene and 7.2 x 10(4) mol product/mol enzyme in amyl acetate. In each solvent, the tyrosinase reaction inactivation parameters were represented by a probabilistic model. Changes in the probability of inactivation were followed throughout the course of the reaction using a second model which relates the reaction velocity to the amount of product formed. These models reveal that the inactivation rate of tyrosinase decreases as the reaction progresses, and that the inactivation kinetics are independent of the quinone concentration in toluene, chloroform, butanol, and amyl acetate. Significant effects of quinone concentration were, however, observed in isopropyl ether. The likelihood of inactivation of the enzyme was found to be greatest toward the beginning of the reaction. In the latter phase of the reaction, inactivation probability was less and tended to remain constant until the completion of the reaction.
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PMID:Tyrosinase inactivation in organic solvents. 1048 31

1. This study made use of a nitric oxide-sensitive electrode to examine possible means of generating nitric oxide from nitroxyl anion (NO(-)) released upon the decomposition of Angeli's salt. 2. Our results show that copper ions (from CuSO(4)) catalyze the rapid and efficient oxidation of nitroxyl to nitric oxide. Indeed, the concentrations of copper required to do so (0.1 - 100 microM) are roughly 100-times lower than those required to generate equivalent amounts of nitric oxide from S-nitroso-N-acetyl-D,L-penicillamine (SNAP). 3. Experiments with ascorbate (1 mM), which reduces Cu(2+) ions to Cu(+), and with the Cu(2+) chelators, EDTA and cuprizone, and the Cu(+) chelator, neocuproine, each at 1 mM, suggest that the oxidation is catalyzed by copper ions in both valency states. 4. Some compounds containing other transition metals, i.e. methaemoglobin, ferricytochrome c and Mn(III)TMPyP, were much less efficient than CuSO(4) in catalyzing the formation of nitric oxide from nitroxyl, while FeSO(4), FeCl(3), MnCl(2), and ZnSO(4) were inactive. 5. Of the copper containing enzymes examined, Cu-Zn superoxide dismutase and ceruloplasmin were weak generators of nitric oxide from nitroxyl, even at concentrations (2500 and 30 u ml(-1), respectively) vastly greater than are present endogenously. Two others, ascorbate oxidase (10 u ml(-1)) and tyrosinase (250 u ml(-1)) were inactive. 6. Our findings suggest that a copper-containing enzyme may be responsible for the rapid oxidation of nitroxyl to nitric oxide by cells, but the identity of such an enzyme remains elusive.
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PMID:Oxidation of nitroxyl anion to nitric oxide by copper ions. 1099 31

1. Our previous finding that copper ions oxidize nitroxyl anion released from Angeli's salt to nitric oxide prompted us to examine if copper-containing enzymes shared this property. 2. The copper-containing enzyme, tyrosinase, which catalyses the hydroxylation of monophenols to diphenols and the subsequent oxidation of these to the respective unstable quinone, failed to generate nitric oxide from Angeli's salt by itself, but did so in the presence of tyrosine. 3. L-DOPA, the initial product of the reaction of tyrosinase with tyrosine, was not the active species, since it failed to generate nitric oxide from Angeli's salt. Nevertheless, L-DOPA and two other substrates, namely, catechol and tyramine did produce nitric oxide from Angeli's salt in the presence of tyrosinase, suggesting involvement of the respective unstable quinones. In support, we found that 1,4-benzoquinone produced a powerful nitric oxide signal from Angeli's salt. 4. Coenzyme Q(o), an analogue of ubiquinone, failed to generate nitric oxide from Angeli's salt by itself, but produced a powerful signal in the presence of its mitochondrial complex III cofactor, ferricytochrome c. 5. Experiments conducted on rat aortic rings with the mitochondrial complex III inhibitor, myxothiazol, to determine if this pathway was responsible for the vascular conversion of nitroxyl to nitric oxide were equivocal: relaxation to Angeli's salt was inhibited but so too was that to unrelated relaxants. 6. Thus, certain quinones oxidize nitroxyl to nitric oxide. Further work is required to determine if endogenous quinones contribute to the relaxant actions of nitroxyl donors such as Angeli's salt.
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PMID:Formation of nitric oxide from nitroxyl anion: role of quinones and ferricytochrome c. 1115 74

A series of N-substituted N-nitrosohydroxylamines including six new compounds were synthesized and examined for inhibition of mushroom tyrosinase. Corresponding hydroxylamines were reacted with n-butyl nitrite to give substituted nitrosohydroxylamines as their ammonium salt. The N-substituted hydroxylamines were prepared from the primary amines via the oxaziridine, or from the carbonyl compounds via the oxime. Most of the nitrosohydroxylamines tested inhibited mushroom tyrosinase. Among them, N-cyclopentyl-N-nitrosohydroxylamine exhibited the most potent activity (IC(50)=0.6 microM), as powerful as that of tropolone, one of the most powerful inhibitors. As removal of nitroso or hydroxyl moiety, the enzyme inhibitory activity was completely diminished. Both N-nitroso group and N-hydroxy group were suggested to be essential for the activity, probably by interacting with the copper ion at the active site of the enzyme. Lineweaver-Burk plotting showed that cupferron was a competitive inhibitor but that N-cyclopentyl-N-nitrosohydroxylamine was not.
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PMID:Synthesis of N-substituted N-nitrosohydroxylamines as inhibitors of mushroom tyrosinase. 1137 81

Bisphenol A was oxidized to monoquinone and bisquinone derivatives by Fremy's salt, a radical oxidant, though salcomine and alkali did not catalyze the oxidation by molecular oxygen. Bisphenol A, bisphenol B, and 3,4'-(1-methylethylidene)bisphenol were converted to their monoquinone derivatives in the presence of tyrosinase at 25 degrees C at pH 6.5, but not to the bisquinone derivatives under these conditions.
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PMID:Oxidation of bisphenol A and related compounds. 1147 53

A heat-labile protein has been identified in fruit bodies of the edible mushroom, Agaricus bisporus, which protects Raji cells (a human lymphoma cell line) against H2O2-induced oxidative damage to cellular DNA. This protein has been purified following salt fractionation, combined with ion-exchange, hydrophobic interaction and adsorption chromatography. Based on catalytic and electrophoretic properties, and inhibition studies using tropolone, the protein was identified as tyrosinase. The genoprotective effect of A. bisporus tyrosinase, determined using the single-cell gel electrophoresis met") assay, has been shown to be dependent upon the enzymic hydroxylation of tyrosine to L-DOPA and subsequent conversion of this metabolite to dopaquinone. The possible role of dopaquinone, and other L-DOPA oxidation products, in enhancing the cellular antioxidant defence mechanisms is discussed.
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PMID:Role of tyrosinase in the genoprotective effect of the edible mushroom, Agaricus bisporus. 1199 Dec 48

To understand conversion of bisphenol A and its related compounds under some chemical and biological environments, oxidation of these compounds was performed. Bisphenol A was oxidized to monoquinone and bisquinone derivatives by Fremy's salt, a radical oxidant; but salcomine and alkali did not catalyze the oxidation by molecular oxygen. Bisphenol A, bisphenol B, and 3,4'-(1-methylethylidene)bisphenol were converted to their monoquinone derivatives in the presence of oxygen and polyphenol oxidase from mushroom at 25 degrees C at pH 6.5. Among crude enzyme solutions of fruits and vegetables, potato, mushroom, eggplant, edible burdock, and yacon showed remarkable oxidative activity on bisphenol A. The highest activity was observed in potato, and the main product obtained by the enzymatic oxygenation was the monoquinone derivative of bisphenol A, accompanied by a small amount of the bisquinone derivative. The oxidation reactions found here will be useful for developing techniques for elimination of phenolic endocrine disrupters from the environment.
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PMID:Oxygenation of bisphenol A to quinones by polyphenol oxidase in vegetables. 1210 73

1. Ovarian tissue from Bombyx mori L. larvae about to pupate was cultured in Trager's (1935) salt solution and 10 per cent hemolymph, with indifferent results. Improvement of cultures was sought by modifying the culture medium. 2. To reduce the activity of the tyrosinase, hemolymph for culture medium was heated for 5 minutes at 60 degrees C., and the coagulated protein removed. 3. A physiological solution was formulated containing cations and amino acids as they occur normally in silkworm hemolymph. In both hanging-drop and small tube cultures use of this medium brought about increased cell number, improved cell appearance, more rapid mitoses, and longer life of cultures. 4. To the solution formulated from analyses, tryptophan, cystine, cysteine, malate, fumarate, succinate, and alpha-ketoglutarate were added after testing individually, resulting in improved growth in cultures. 5. Use of a silkworm egg extract prepared 4 to 5 days after acid treatment produced an increase in cell number. 6. In small roller tube cultures, when the new medium was changed twice a week, the cells spread over the walls of the tube in 4 or 5 days (Figs. 8 and 9), rapid mitoses were observed after 2 weeks, and transparent active cells were present at 3 weeks. Subculturing was not attempted.
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PMID:Culture in vitro of tissue from the silkworm, Bombyx mori L. 1334 39

Sponges (phylum Porifera), known to be the richest producers among the metazoans of bioactive secondary metabolites, are assumed to live in a symbiotic relationship with microorganisms, especially bacteria. Until now, the molecular basis of the mutual symbiosis, the exchange of metabolites for the benefit of the other partner, has not been understood. We show with the demosponge Suberites domuncula as a model that the sponge expresses under optimal aeration conditions the enzyme tyrosinase, which synthesizes diphenols from monophenolic compounds. The cDNA isolated was used as a probe to determine the steady-state level of gene expression. The gene expression level parallels the level of specific activity in sponge tissue, indicating that without aeration the tyrosinase level drops drastically; this effect is reversible. The SB2 bacterium isolated from the sponge surface grew well in M9 minimal salt medium supplemented with the dihydroxylated aromatic compound protocatechuate; this carbon source supported growth more than did glucose. From the SB2 bacterium the protocatechuate gene cluster was cloned and sequenced. This cluster comprises all genes coding for enzymes involved in the conversion of protocatechuate to acetyl coenzyme A. Expression is strongly induced if the bacteria are cultivated on M9-protocatechuate medium; the genes pcaQ (encoding the putative transcriptional activator of the pca operon) and pcaDC were used for quantitative PCR analyses. We conclude that metabolites, in this case diphenols, which might be produced by the sponge S. domuncula are utilized by the sponge surface-associated bacterium for energy generation. This rationale will help to further uncover the symbiotic pathways between sponges and their associated "nonculturable" microorganisms; our approach is flanked by the establishment of an EST (expressed sequence tags) database in our laboratory.
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PMID:Oxygen-controlled bacterial growth in the sponge Suberites domuncula: toward a molecular understanding of the symbiotic relationships between sponge and bacteria. 1506 29


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