Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.10.3.1 (tyrosinase)
 9,065 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two melanotic human melanoma cell lines, IRE 1 and IRE 2, and the lymphoma- and leukaemia-derived cell lines Raji and K 562, were exposed to different concentrations (from 5 X 10(-3) M to 10(-5) M) of phenols, both substrates (s) and non-substrates (ns) of tyrosinase, in the presence or absence of the oxygen-radical-scavenger enzymes superoxide dismutase, catalase and peroxidase. Monophenols were tyrosine (s), 4-hydroxyanisole (s) and butylated hydroxyanisole (ns); diphenols were L-3,4-dihydroxyphenylalanine (s), dopamine (3,4-dihydroxyphenethylamine) (s), terbutylcatechol (s), hydroquinone (s) and resorcinol (ns); triphenols were 6-hydroxydopa (3,4,6-trihydroxyphenylalanine) (s) and methyl gallate (s). Triphenols and o- and p-diphenols underwent complete oxidation in culture medium within 24 h of incubation and were significantly more toxic than monophenols and the m-diphenol resorcinol, which, under the same cultural conditions, were much more stable. No significant differences in percentage survival were found among the different cell lines for each drug tested. The major component of toxicity up to 24 h of di- and tri-phenols is due to toxic oxygen species acting outside the cells and not to cellular uptake of these phenols as such. In fact the addition of oxygen-radical-scavenger enzymes significantly (P less than 0.01) decreased the adverse effect of these drugs on all cell lines. The lower toxicity of monophenols and resorcinol as compared with that of di- and tri-phenols is due, in our opinion, to the fact that they are less oxidized under the conditions existing in the culture medium, and therefore do not produce sufficient levels of oxygen radicals. For these compounds, a primary intracellular action has to be taken into account to explain their cytotoxicity.
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PMID:Comparative cytotoxicity of phenols in vitro. 282 25

The visual field representation and functional architecture of cortical areas 17 and 18 in albino cats were studied. In the same animals the distributions of ipsilaterally and contralaterally projecting retinal ganglion cells were determined by injecting horseradish peroxidase into the dorsal lateral geniculate nucleus or optic tract. All cats were tyrosinase-negative albinos (cc), not deaf white cats (W). The proportion of ipsilaterally projecting ganglion cells in the temporal retina of the albino cat was found to be much smaller than in the normal cat or in the Siamese cat. In the albino cat less than 5% of ganglion cells in temporal retina project ipsilaterally. Recordings from areas 17 and 18 provided evidence of a substantial representation of the ipsilateral hemifield in albino visual cortex; cells representing the contralateral and ipsilateral hemifields were often segregated into alternating zones in area 17 and were always segregated in area 18. Cells recorded at the borders of zones representing the ipsilateral and contralateral hemifields often had abnormal properties. Some border cells had two receptive fields separated by as much as 60 degrees of azimuth; one field subserved the contralateral hemifield (contralateral nasal retina) and the other subserved the mirror-symmetric part of ipsilateral hemifield (contralateral temporal retina). Receptive fields of cells subserving the two hemifields did not differ in size. The preferred orientations, preferred velocities, and other characteristics of the two fields were approximately the same; preferred orientation changed gradually and systematically across the borders of zones representing the two hemifields. Our results indicate that afferents representing nasal and temporal regions of retina of the same eye can segregate and form "hemiretina" domains in albino visual cortex. These afferents can also converge upon individual cortical cells in a fashion reminiscent of convergence of afferents from the two eyes upon binocular cells in the normal cortex. The organization of albino visual cortex is therefore different from the organization of Siamese visual cortex. This may be because, in the albino cat but not the Siamese cat, nearly all cells in temporal retina project contralaterally; afferents representing contralateral temporal retina are not at a significant competitive disadvantage in the albino.
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PMID:Retinal projections and functional architecture of cortical areas 17 and 18 in the tyrosinase-negative albino cat. 298 49

Electron spin resonance spectroscopy has been used to demonstrate production of semiquinone free radicals from the oxidation of the catechol estrogens 2- and 4-hydroxyestradiol and 2,6- and 4,6-dihydroxyestradiol. Radicals were generated by horseradish peroxidase/H2O2 or tyrosinase/O2, or by autoxidation, and were detected as their complexes with spin-stabilizing metal ions (Zn2+ and/or Mg2+). Radical production occurs via one- or two-electron oxidation of catechol estrogens, depending on the type of activating system. Autoxidation of catechol estrogens produces superoxide and H2O2 at physiological pH values. The present results also indicate a difference in the reactivity of quinones derived from 2- and 4-hydroxyestradiol. The toxicological significance of these reactions is discussed.
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PMID:An electron spin resonance study of free radicals from catechol estrogens. 301 66

A sensitive, specific, competitive enzyme-linked immunosorbent assay (ELISA) was developed for quantitative analysis of tyrosinase. Binding sites of anti-tyrosinase antibodies were competed for by purified tyrosinase adsorbed onto microtiter plates and a known (standard) or unknown (sample) amount of tyrosinase in solution. Adsorbed antibodies were detected by goat anti-rabbit IgG F(ab')2 labeled with peroxidase. A sensitivity range of 2.1 to 14 ng (30-200 fmol)/well was obtained. SDS was found to be the most suitable detergent for solubilizing the enzyme. Tyrosinase was extracted from B16 mouse melanoma and assayed by the ELISA. The tyrosinase content per mg melanoma protein was 505 +/- 106 (S.D.) ng. This assay is not only useful for measuring the content of normal tyrosinase in crude extracts but also is possibly applicable to detecting the unprocessed tyrosinases.
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PMID:Quantitative analysis of mouse tyrosinase by enzyme-linked immunosorbent assay. 308 1

Tyrosinase usually catalyzes the conversion of monophenols to o-diphenols and oxidation of diphenols to the corresponding quinones. However, when 3,4-dihydroxymandelic acid was provided as the substrate, it catalyzed an unusual oxidative decarboxylation reaction generating 3,4-dihydroxybenzaldehyde as the sole product. The identity of the product was confirmed by high-performance liquid chromatography (HPLC) as well as ultraviolet and infrared spectral studies. None of the following enzymes tested catalyzed the new reaction: galactose oxidase, ceruloplasmin, superoxide dismutase, ascorbate oxidase, dopamine beta-hydroxylase, and peroxidase. Phenol oxidase inhibitors such as phenylthiourea, potassium cyanide, and sodium azide inhibited the reaction drastically, suggesting the participation of the active site copper of the enzyme in the catalysis. Mimosine, a well-known competitive inhibitor of tyrosinase, competitively inhibited the new reaction also. 4-Hydroxymandelic acid and 3-methoxy-4-hydroxymandelic acid neither served as substrates nor inhibited the reaction. Putative intermediates such as 3,4-dihydroxybenzyl alcohol and (3,4-dihydroxybenzoyl)formic acid did not accumulate during the reaction. Oxidation to a quinone methide derivative rather than conventional quinone accounts for this unusual oxidative decarboxylation reaction. Earlier from this laboratory, we reported the conversion of 4-alkylcatechols to quinone methides catalyzed by a cuticular phenol oxidase [Sugumaran, M., & Lipke, H. (1983) FEBS Lett. 155, 65-68]. Present studies demonstrate that mushroom tyrosinase will also catalyze quinone methide production with the same active site copper if a suitable substrate such as 3,4-dihydroxymandelic acid is provided.
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PMID:Tyrosinase catalyzes an unusual oxidative decarboxylation of 3,4-dihydroxymandelate. 309 74

Cell lines Raji and K 562, lacking tyrosinase, and two melanotic human melanoma cell lines (IRE 1 and IRE 2), were exposed to concentrations from 5 X 10(-3) M to 10(-5) M of different phenols which are substrates of tyrosinase, i.e. l-dopa, dopamine, hydroquinone, terbutylcatechol, and of phenols which are not substrates of the tyrosinase, i.e. resorcinol, butylated hydroxyanisole and hydroquinone dimethyl ether. Cultures were carried out in the presence or in the absence of oxygen radical scavenger enzymes superoxide dismutase, catalase and peroxidase. The stability of each substance in culture medium was assayed by high performance liquid chromatography (HPLC). Results showed that: catechols which are substrates of tyrosinase decompose fully after 24 hr in medium; they are equally toxic for melanoma and non-melanoma cell lines; their toxicity increases when they are preincubated in medium for 24 hr and 48 hr before addition of cells; their toxicity is significantly reduced by addition of scavenger enzymes; on the contrary, phenols not substrates of tyrosinase are stable in medium and their toxicity is not reduced by scavenger enzymes. It is concluded that tyrosinase does not play a major role in catechol toxicity in vitro, which is probably due to some products of catechol decomposition, especially oxygen radicals, acting outside the cells.
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PMID:Mechanism of antitumoral activity of catechols in culture. 310 24

Ultraweak luminescence in the spectral region 300-660 nm is generated in the enzymatic (tyrosinase EC.1.14.18.1) and autooxidative polymerization of L-DOPA, 5-S-cysteinyl-DOPA, and L-DOPA + cysteine to eumelanins and pheomelanins, respectively. Using sensitive calibrated single photon counting equipment, the photon emission intensity I and quantum yield phi have been measured: I = 10-100 h nu/s cm3, phi less than or equal to 10(-13) for enzymatic reactions, and I = 500-3000 h nu/s cm3, phi greater than or equal to 5 x 10(-12) for autooxidative ones. 5-S-cysteinyl-DOPA and cysteine exhibit diminished I and phi-values relative to DOPA. Tests with chemiluminogenic probes-luminol and lucigenin, SOD, catalase, peroxidase, H2O2, and spectrophotometric measurements indicate that photon emission is associated with degradative oxidations of melanin subunits by means of active oxygen species as H2O2 and O2.
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PMID:Ultraweak photon emission in model reactions of the in vitro formation of eumelanins and pheomelanins. 314 40

A variety of factors were found to modify the toxicity of L-dopa in HeLa cells (D37 16 microM) and in dopa-sensitive, nonpigmented human melanoma cells (MM96) (D37 5 microM) having a similar size and doubling time. Dopa toxicity was decreased by concurrent treatment with superoxide dismutase, peroxidase or catalase, by erythrocytes, or by hypoxia. Toxicity could be increased by the enzyme inhibitors L- and D-penicillamine, sodium diethyldithiocarbamate or 3-amino-1,2,4-triazole. The two cell lines had similar levels of superoxide dismutase and peroxidase; in 6 human melanoma lines, no correlation was found between dopa killing and tyrosinase activity as determined either by formation of dopa from tyrosine or by formation of melanin from dopa. Uptake of L-dopa was similar in HeLa and MM96 cells, and the toxicity of D-dopa was the same in both lines as that of the L-isomer. Dopa decomposed within 12 hr in culture medium, the rate and products being influenced by addition of the above enzymes and by the cell density. Dopa-melanin and medium containing decomposed dopa were also selectively toxic to MM96 cells. Adenovirus 5 was used in two different ways to assess the relative importance of DNA damage and inhibition of DNA synthesis by dopa. Viral replication was found to be unaffected in cells being treated with dopa but was strongly inhibited in cells treated with the DNA polymerase inhibitor cytosine arabinoside. Secondly, the virus was itself inactivated by treatment with dopa for 24 hr (D37 1.3 mM); similar dose response curves were obtained for replication of dopa-treated virus in untreated HeLa or MM96 cells. These results show that the initial events of dopa toxicity occur outside the cell and lead to the formation of a stable, toxic product (probably melanin) which does not strongly inhibit DNA polymerase activity. Melanoma hypersensitivity was not due to differences in oxygen-metabolizing enzymes, dopa uptake, or DNA repair.
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PMID:Modification of dopa toxicity in human tumour cells. 392 49

Acanthamoeba castellanii has a phenol oxidase activity that is believed to be a laccase. Enzyme activity was found in the outer cyst wall, in the cytoplasm of encysting amoebae and in the encystment medium. Encystment procedures were modified to promote an increase in the amount of soluble enzyme secreted during encystation. Acanthamoeba polyphenol oxidase has a pH optimum of 6.0 and a Km value of 0.21 mM with dihydroxyphenylalanine. The enzyme does not oxidize tyrosine, and it is inhibited by chloride but not by inhibitors of peroxidase. Its synthesis coincides with encystation, and known inhibitors of polyphenol oxidase prevent encystation. Polyphenol oxidase may have a role in making the cyst resistant to mechanical and chemical breakdown.
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PMID:Polyphenol oxidase produced during encystation of Acanthamoeba castellanii. 393 Jul 6

Peroxide-dependent enzymic oxidation of tyrosine to dopachrome and melanin was demonstrated in cell-free melanoma homogenates. Histochemical methods for distinguishing peroxidase activity from aerobic dopa (3,4-dihydroxyphenylalanine) oxidase activity are not reliable with cell-free preparations. Therefore the presence of peroxidase activity in such preparations precludes assay of cresolase activity of mammalian ;tyrosinase'.
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PMID:Peroxidatic oxidation of tyrosine to melanin in supernatant of crude mouse melanoma homogenates. 444 86


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