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)

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

Isozymes of tobacco pith polyphenoloxidases (o-diphenol oxidase, EC 1.10.3.1) were separated electrophoretically from fresh pith of intact plants and from cultured pith sections. Extracts of fresh pith contained a poorly resolved complex of two to three anodic bands after starch gel electrophoresis at alkaline pH. This anodic complex was more active with chlorogenic acid than with 3,4-dihydroxyphenylalanine and was found in greater activity per gram fresh weight of tissue in younger internodes than in older ones. The longitudinal gradient of activity was thus the opposite of that found for the constitutive isozymes of peroxidase.A well defined cathodic band of polyphenoloxidase activity appeared after culture of pith in modified White's medium with shaking. This band, which was more active with 3,4-dihydroxyphenylalanine than with chlorogenic acid, could be detected after 1 to 2 days of incubation. Its appearance was enhanced by the addition of 10 mum indoleacetic acid; kinetin (1 mum tended to prevent this indoleacetic acid effect). Such hormonal control is opposite to that previously reported for the rapidly appearing new isozymes of peroxidase. The pattern of the major isozymes associated with polyphenoloxidase activities differs from that of peroxidase.
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PMID:Ontogeny and hormonal control of polyphenoloxidase isozymes in tobacco pith. 499 42

The availability of very high magnetic fields of up to 170,000 gauss made it worthwhile to pursue the search for a critical change in the rate of four enzyme substrate reactions. The four enzymes were ribonuclease, polyphenol oxidase, peroxidase, and aldolase. The experiments showed that, to within +/-3%, no detectable change was observable in the rate of reaction of any of the systems for periods of exposure to the magnetic field of up to 20 min.
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PMID:Enzyme-substrate reactions in very high magnetic fields. I. 604 70

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 either enzymatically (using horseradish peroxidase-H2O2 or tyrosinase-O2) or by autoxidation, and were detected as their complexes with spin-stabilizing metal ions (Zn2+ and/or Mg2+). In the peroxidase system, radicals are produced by one-electron oxidation of the catechol estrogen and their decay is by a second-order pathway, consistent with their disproportionation to quinone and catechol products. With tyrosinase-O2, radical generation occurs indirectly. Initial hydroxylation of phenolic estrogen (at either the 2- or 4-position) gives a catechol estrogen in situ; subsequent two-electron oxidation of the catechol to the quinone, followed by reverse disproportionation, leads to the formation of radicals. A competing mechanism for radical production involves autoxidation of the catechol. Results obtained from the estrogen systems have been compared with those from the model compound 5,6,7,8-tetrahydro-2-naphthol.
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PMID:An electron spin resonance study of o-semiquinones formed during the enzymatic and autoxidation of catechol estrogens. 609 35

The ability to degrade oligo- and polysaccharides by enzymes of the glycosidase and glucan-glucan hydrolyse type, and esterase, phosphatase, proteinase, peroxidase, catalase, laccase and tyrosinase activities were tested in 35 strains of 11 sections of the genus Fusarium.
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PMID:Enzyme apparatus of the genus Fusarium. 624 4

Incubation of native human 125I-IgG with polymorphonuclear neutrophil (PMN) peroxidase-containing granules or with purified myeloperoxidase (MPO) in the presence of H2O2 and a suitable hydrogen donor such as catechol generated large amounts of heavy IgG aggregates. Short-term incubation (15 to 60 min) of native 125I-IgG (400 microgram) with MPO-containing granules or with purified MPO (1.5 microgram) in the presence of H2O2 (0.036 to 0.36 mumol) and catechol (0.2 mumol) resulted in the generation of 8 to 100 microgram of heavy IgG aggregates (3 X 10(5) to 4 X 10(6) daltons). Aggregate formation was completely abolished by the omission of H2O2 or catechol, and by the addition of catalase, sodium azide, or cyanide. IgG aggregates were also generated with tyrosinase, tyrosine, and atmospheric oxygen. These results indicate that aggregation was due to MPO-H2O2-mediated oxidation of catechol to orthoquinone, which was deemed to be directly responsible for cross-linking by non-enzymic biochemical reactions. The IgG aggregates generated were shown to behave as typical immune complexes in that they consumed C, were detected by the solid-phase C1q and Raji cell assays, and were precipitable by monoclonal rheumatoid factor. This nonspecific oxidative protein-aggregation reaction may play an important role in the pathogenesis of tissue injury in acute and chronic inflammatory processes and in drug reactions. It could also provide an explanation for the frequent detection of circulating immune complex-like material in a large variety of acute and chronic inflammatory states.
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PMID:Generation of IgG aggregates by the myeloperoxidase-hydrogen peroxide system. 630 Feb 34

The permeability of junctional complexes to ultrastructural tracers of different molecular weight and the freeze-fracture appearance of junctional structure were investigated in the resting and stimulated rat parotid gland. Tracers were administered retrogradely via the main excretory duct, and allowed to flow by gravity (16 mmHg) into the gland for 15-60 min. Secretion was induced in some animals by intraperitoneal injection of isoproterenol. In resting glands, the tracers microperoxidase , cytochrome c, myoglobin, tyrosinase (subunits), and hemoglobin were restricted to the luminal space of the acini and ducts. In glands stimulated 1-4 h before tracer administration, reaction product for microperoxidase , cytochrome c, myoglobin, and tyrosinase was found in the intercellular and interstitial spaces, whereas hemoglobin was usually retained in the lumina. In contrast, horseradish peroxidase and lactoperoxidase appeared to penetrate the tight junctions and reaction product was localized in the extracellular spaces in both resting and stimulated glands. Diffuse cytoplasmic staining for horseradish peroxidase and lactoperoxidase was frequently observed in acinar and duct cells. The distribution of horseradish peroxidase was similar in both Sprague-Dawley and Wistar-Furth rats, and at concentrations of 0.1-10 mg/ml in the tracer solution. Freeze-fracture replicas of stimulated acinar cells revealed an increased irregularity of the tight junction meshwork, but no obvious gaps or discontinuities were observed. These findings indicate that (a) tight junctions in the resting rat parotid gland are impermeable to tracers of molecular weight greater than or equal to 1,900; (b) stimulation with isoproterenol results in a transient increase in junctional permeability allowing passage of tracers of molecular weight less than or equal to 34,500; (c) junctional permeability cannot be directly correlated with junctional structure; and (d) the behavior of horseradish peroxidase and lactoperoxidase in the rat parotid gland is inconsistent with their molecular weights. Cell membrane damage due to the enzymatic activity or binding of these two tracers may account for the observed distribution.
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PMID:Alteration of tight junctional permeability in the rat parotid gland after isoproterenol stimulation. 672 2

Quantitative histochemical measurements of activities of enzymes were performed by temporal defined stages in development of Protophormia terraenovae. The effect of the specific insecticide of moult Duphar pH 60-38 activity of enzyme was evaluated. Activities of peroxidase and tyrosinase showed parallel oscillations, at which proof of both enzymes was restricted to the cuticle. The insects, treated with insecticide, showed a moulting, dependent on concentration. A transfer of maxima of activities is described.
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PMID:[Histochemical study of peroxidase and tyrosinase activities in the cuticle of Protophormia terraenovae]. 676 71

Desialylated glycoproteins were covalently linked to two cytochemically detectable enzymes, horseradish peroxidase or tyrosinase, and injected intravenously in amounts of approximately 0.5 per cent of total plasma glycoproteins into rats. Comparative studies of the rates of disappearance and distribution of free enzyme and conjugates established that recognition of the conjugates by the plasma membranes of hepatocytes was due to the exposure of the terminal galactose residue of the desialylated glycoproteins. At 1 minute after injection, reaction products of the enzyme markers were seen in coated pits and vesicles, elongated pinocytic channels and pleomorphic vesicles, at or close to the sinusoidal surface of hepatocytes. Vesicles containing reaction products were also observed along the lateral surfaces of hepatocytes. By 10 minutes, reaction products were seen in residual bodies near the biliary poles of hepatocytes. These studies confirm the existence of hepatocellular channels previously seen only with large excess of hemoglobin or following partial hepatectomy. They also indicate that the specific receptor for asialoglycoproteins is not restricted to the sinusoidal surfaces of hepatocytes and that transport to the catabolic sites proceeds via cytoplasmic channels and vesicles.
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PMID:Endocytosis of asialoglycoprotein-enzyme conjugates by hepatocytes. 677 3


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