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)

Two forms of cutaneous albinism in the chicken were investigated for the presence and distribution of tyrosinase and acid phosphatase in melanocytes in situ and in culture. In sex-linked recessive tyrosinase-positive albinism, sal, melanocytes in regenerating feathers and neural tube-derived cultures contained morphologically normal and abnormal premelanosomes. Tyrosinase was localized primarily to the abnormal premelanosomes and probably not to the normal ones. The cells possessed, in addition, vacuoles with membranous inclusions, located in the dendrites, and capped by dopa-positive vesicles (capping vesicles). Acid phosphatase colocalized with tyrosinase in the abnormal premelanosomes and capping vesicles. Tyrosinase activity in extracts of cultured sal melanocytes equalled that of e+ control melanocytes. A tyrosinase antiserum, raised against hamster tyrosinase (Pomerantz), precipitated 2 proteins, 68 kD and 82 kD, which had a precursor-product relationship. The amount of immunoprecipitate was the same in sal and control extracts, but in sal extracts the lower-molecular-weight protein was twice as abundant as the higher-molecular-weight protein. Melanocytes in regenerating feathers from an autosomal recessive, tyrosinase-negative albino, ca, also contained morphologically normal and abnormal premelanosomes. In culture, ca melanocytes had no formal premelanosomes but only dopa-negative multivesicular bodies with wispy filamentous material. Tyrosinase activity and immunoprecipitable tyrosinase were absent. These results suggest that: the tyrosinase-positive albino, sal, has an aberration in both its tyrosinase and acid phosphatase profiles and the tyrosinase-negative albino, ca, lacks functionally and antigenically normal tyrosinase.
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PMID:Tyrosinase and acid phosphatase activities in melanocytes from avian albinos. 310 23

Tyrosinase has a suicide inactivation reaction when it acts on omicron-diphenols. In the present paper, this reaction has been studied using a transient phase approach. Explicit equations of product vs. time have been developed for the multisubstrate mechanism of tyrosinase, and the kinetic parameters which characterize the enzyme acting on the suicide substrate catechol have been determined. The effect of pH has also been considered.
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PMID:Kinetic study on the suicide inactivation of tyrosinase induced by catechol. 310 85

This study was directed towards the characterization of the origin of the microheterogeneity displayed by mammalian tyrosinase, the enzyme responsible for pigmentation in mammals. Tyrosinase was purified from the Harding Passey murine melanoma, fractionated into a continuous series of subisozymic forms, and analyzed using various chemical and immunological probes. Treatment with neuraminidase revealed that all the forms had similar amounts of sialic acid, and reactivity with various carbohydrate specific lectins showed that the isozymes also contained subterminal galactose, N-acetylglucosamine, and mannose, but lacked alpha-fucose. Amino acid composition data indicated that the polypeptides of all the forms had identical residue contents. The sum of the evidence further supports the theory that the isozymic forms demonstrable for mammalian tyrosinase represent intermediate processing stages of the enzyme from the nascent protein chain to the fully glycosylated, high molecular weight form of tyrosinase that is localized within melanin granules.
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PMID:Microheterogeneity of melanosome-bound tyrosinase from the Harding-Passey murine melanoma. 310 72

Tyrosinase, which usually catalyzes the conversion of o-diphenols to o-benzoquinones, catalyzed an unusual oxidative dimerization of 1,2-dehydro-N-acetyl-dopamine to a benzodioxan derivative. The identity of the product was confirmed by UV, IR spectra, and NMR studies. During the oxidation, generation of a transient reactive intermediate could be witnessed by its characteristic visible absorption spectrum. Typical phenoloxidase inhibitors such as phenylthiourea, potassium cyanide, sodium azide, and sodium fluoride drastically inhibited the above reaction. Mimosine, a known competitive inhibitor of o-diphenoloxidase activity, also inhibited the new reaction competitively, suggesting that both the observed oxidative dimerization and the conventional quinone production are catalyzed by the same active site copper of tyrosinase. Based on our earlier findings (Sugumaran, M., and Lipke, H. (1983) FEBS Lett. 155, 65-68; Sugumaran, M. (1986) Biochemistry 25, 4489-4492) that phenoloxidases can produce quinone methides from certain 4-alkylcatechols, possible mechanisms for this new reaction are presented.
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PMID:Tyrosinase-catalyzed unusual oxidative dimerization of 1,2-dehydro-N-acetyldopamine. 311 46

1. Tyrosinase was purified from melanosomal fraction of hamster melanoma. 2. A radioimmunoassay was developed to quantitate the tyrosinase protein in hamster serum and hamster melanoma tissue using polyclonal anti-tyrosinase antibodies and 125I-labeled enzyme. 3. The serum tyrosinase levels were found to be about 0.24 micrograms and 1.14-4.48 micrograms/ml in normal hamsters and melanoma-bearing hamsters, respectively. 4. Tyrosinase protein in serum correlated significantly with the enzyme activity in hamsters with melanoma (r = 0.733). 5. In the cytosol fraction of hamster melanoma, a level of 2.2 micrograms of tyrosinase/mg protein was determined. 6. The usefulness and possible applications of the tyrosinase radioimmunoassay are discussed.
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PMID:Tyrosinase of hamster melanoma: its purification and estimation by radioimmunoassay. 311 84

A spontaneous, hypomelanotic variant (MI) of the highly melanotic transplantable hamster melanoma of Bomirski (Ma) is the subject of this report. Tyrosinase activity is 2-3 times higher, but melanin content significantly lower than in the parental Ma melanotic melanoma. Acid phosphatase activity is similar in both, but beta-glucuronidase and aryl-sulfatase A are 2-3 times higher in the hypomelanotic variant. Transplanted MI melanomas grow more slowly than the parental tumor, but metastasize with similar incidence and localization. Hypomelanotic variant melanoma cells, even those in grossly nonnecrotic parts of the transplants, show signs of low viability like swelling of the cytoplasm or cellular condensation, and disintegration. Autophagic vacuoles are numerous. They appear to be formed by enclosure of a portion of cytoplasm by cisternae of smooth endoplasmic reticulum or trans-Golgi network. These limiting cisternae contain tyrosinase as evidenced by deposition of electron dense reaction product on incubation with tyrosine or DOPA. Other sites of ultrastructural tyrosinase reaction are melanosomes and the smooth-surfaced cisternae and vesicles of the trans-Golgi network. We postulate the low cell viability, associated with autophagosome formation, is the cause for the growth retardation of the MI variant, and that the lower melanin content of these tyrosinase-rich cells is due to sequestration of a substantial portion of newly synthesized enzyme into autophagic vacuoles before it has the chance of being incorporated into melanosomes.
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PMID:Pathology and ultrastructural characteristics of a hypomelanotic variant of transplantable hamster melanoma with elevated tyrosinase activity. 311 4

Tyrosinase activity at the time of phaeomelanin synthesis in neonatal mice is lower in agouti than in black skin and hair bulb tissue, and this depressed activity is associated with a reduction in the electrophoretically distinct de novo form of the enzyme. Direct chemical measurements of sulphydryl compounds show elevated levels in agouti hair bulb tissue at this stage of development. The addition of exogenous copper to hair bulb extracts raises the activity of tyrosinase in agouti to approximately the black level but has no affect on black itself. These results are discussed in relation to the role of sulphydryl compounds and copper availability in regulating tyrosinase activity and turnover.
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PMID:Tyrosinase activity and the expression of the agouti gene in the mouse. 311 67

1. Tyrosinase is a copper-containing enzyme responsible for the production of melanin pigment throughout the phylogenetic spectrum. 2. In mammals, tyrosinase is a glycosylated enzyme found specifically in melanocytes--cells functional in the production and secretion of pigment granules. 3. Although many factors determine the type, quantity and quality of the melanin produced, tyrosinase activity is the critical factor that ultimately regulates melanogenesis.
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PMID:Mammalian tyrosinase--the critical regulatory control point in melanocyte pigmentation. 312 75

Tyrosinase (monophenol monooxygenase; monophenol, L-dopa:oxygen oxidoreductase, EC 1.14.18.1) is a key enzyme in the synthesis of melanin. Reduced levels of tyrosinase play an important role in albinism. The data described here show differences in the expression and characteristics of tyrosinase in cutaneous murine melanocytes grown in culture from normal wild-type strains (C/C); from three albino locus mutants: himalayan (ch/ch), chinchilla (cch/cch), and albino (c/c); and from the double-mutant heterozygous pink-eyed chinchilla (cchp/cp). Our results suggest that the diminished pigmentation in all mutants is due to abnormal posttranslational modification of the enzyme: the levels of mRNA for tyrosinase in wild-type, himalayan, and pink-eyed chinchilla melanocytes are similar; the himalayan mutation confers a deficiency in N-linked glycosylation, which results in an extremely unstable enzyme that is also temperature sensitive; the chinchilla and albino mutations confer susceptibility to proteolytic cleavage; the pink-eye dilution confers a reduction in the levels of immunoprecipitable tyrosinase, and what little enzyme there is fails to be translocated from the trans-Golgi network to melanosomes. The kinetics of activation and inhibition of the enzyme by the cofactor dopa are unique for the mutants tested and differ from those of tyrosinase from wild-type melanocytes. The findings support the conclusion that the albino locus in mice encodes the structural gene of tyrosinase.
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PMID:Tyrosinases of murine melanocytes with mutations at the albino locus. 314 Feb 37

Tyrosinase usually catalyses the conversion of monophenols into o-diphenols and the oxidation of diphenols to the corresponding o-quinones. Sugumaran [(1986) Biochemistry 25, 4489-4492] has previously proposed an unusual oxidative decarboxylation of 3,4-dihydroxymandelate catalysed by tyrosinase. Our determination of the intermediates involved in the reaction demonstrated that 3,4-dihydroxybenzaldehyde is not the first intermediate appearing in the medium during the enzymic reaction. Re-examination of this new activity of tyrosinase has demonstrated that the product of the enzyme action is the o-quinone, which, owing to its instability, evolves to the final product, 3,4-dihydroxybenzaldehyde, by a chemical reaction of oxidative decarboxylation.
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PMID:Chemical and enzymic oxidation by tyrosinase of 3,4-dihydroxymandelate. 314 78


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