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)

Golgi complex and endoplasmic reticulum (ER) were isolated from suspension-cultured cells of sycamore (Acer pseudoplatanus L.) by stepwise sucrose density gradient centrifugation using protoplasts as starting material. The purity of the two organelle fractions isolated was assessed by measuring marker enzyme activities. Localization of glycolipid and glycoprotein glycosyltransferase activities in the isolated Golgi and ER fractions was examined; three glycosyltransferases, i.e., galactosyltransferase, fucosyltransferase, and xylosyltransferase, proved to be almost exclusively confined to the Golgi, whereas the ER fractions contained glycolipid glycosyltransferase. The Golgi complex was further subfractionated on a discontinuous sucrose density gradient into two components, migrating at densities of 1.118 and 1.127 g/cm3. The two fractions differed in their compositional polypeptide bands discernible from Na-dodecylsulfate gel electrophoresis. Galactosyltransferase distributed nearly equally between the two protein peaks and xylosyltransferase activities using the endogenous acceptor also appeared to be localized in the two subcompartments. By contrast, fucosyltransferase, engaged in the terminal stage of glycosylation, banded in the lower density fractions. Golgi-specific alpha-mannosidase, which is presumably engaged in the sugar trimming of Asn-N-linked glycoprotein carbohydrate core, was enriched fourfold in specific activity in the fractions of the higher density. The overall experimental results indicate that the cotranslational glycosylation of Asn-N-linked glycoproteins, e.g., polyphenol oxidase (laccase), takes place in the ER, while subsequent post-translational processing of the oligosaccharide moiety proceeds successively in the two physically separable compartments of the Golgi complex.
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PMID:Golgi-specific localization of transglycosylases engaged in glycoprotein biosynthesis in suspension-cultured cells of sycamore (Acer pseudoplatanus L.). 309 42

Pigmentation-associated antigen (PAA) or gp75 is a glycoprotein localized to the melanosomes of human melanomas and melanocytes to which a mouse monoclonal antibody (AbTA99) has been produced (T. M. Thomson et al. (1985) J. Invest. Dermatol. 85, 169). Treatment of 3H-labeled immunoprecipitated melanoma PAA with alkaline-borohydride, hydrazinolysis, or N-glycanase released three families of carbohydrate chains (I, II, and III). Peak I consists of a major component (Ia) of sialylated triantennary N-linked chains which are partially substituted with fucose on terminal positions as well as on the chitobiose core and a minor component (Ib) which is a sialylated biantennary N-linked species. Peak II was not well characterized but may be a monoantennary complex chain species. Peak III consists of typical N-linked high mannose units with six to seven mannose residues. Melanocyte PAA carbohydrate chains have the same general features as melanoma PAA except that the biantennary complex chain predominates; this difference resembles that observed between the cell surface glycopeptides of transformed animal cells and their nontransformed counterparts. The glycosylation characteristics of this melanosomal glycoprotein are compared with those of glycoproteins from endoplasmic reticulum, Golgi, and lysosomes, and with tyrosinase. It is suggested that the glycosylation pattern is a reflection of the biosynthetic origin and cellular destination of a particular organelle and its constituents.
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PMID:Glycosylation characteristics of pigmentation-associated antigen (GP75): an intracellular glycoprotein of human melanocytes and malignant melanomas. 353 23

Pigmented melanoma cells and cultured melanocytes express a differentiation-related glycoprotein designated as pigmentation-associated antigen (PAA) of Mr 70,000-80,000. As described previously, PAA was initially defined by reactivity with antibodies in the serum of a patient with melanoma. Here we describe the production and characterization of a mouse monoclonal antibody to PAA. This antibody (TA99, an IgG2a) was shown by sequential immunoprecipitation experiments to react with the same component as the human antibody. Ab TA99 immunoprecipitated PAA from lysates of cells radiolabeled with [35S]methionine, [3H]glucosamine, [3H]fucose, and [3H]mannose as well as 125I. Using Ab TA99, the distribution of PAA was examined in frozen sections of 19 normal tissues and quantitatively in 68 tissue culture cell lines. In frozen sections, only melanin-containing cells were positive, including epithelial cells in the basal layer of the epidermis, in which pigment originates from melanocytes by transfer of melanosomes, and pigmented cells of the eye. In tissue culture cell lines, only pigmented melanoma cells were positive. PAA is an intracellular antigen, with a distribution very similar to that of melanosomes. This evidence confirms the close association of PAA with melanin production, and suggests that PAA may be a melanosome component. PAA was shown to be different from tyrosinase, the enzyme involved in melanin synthesis, but it was found to be identical to the previously recognized glycoprotein, gp75, characteristic of pigmented melanomas and melanocytes.
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PMID:Pigmentation-associated glycoprotein of human melanomas and melanocytes: definition with a mouse monoclonal antibody. 392 6

A tyrosinase has been purified from the skin of the frog Xenopus laevis. Dihydroxyphenylalanine oxidase and tyrosine hydroxylase activities co-purify throughout the procedure. The enzyme is isolated in an inactive form, but both enzymatic activities are activated by a variety of anionic detergents. Of these, sodium dodecyl sulfate (NaDodSO4) is the most effective. The enzyme activation occurs at NaDodSO4 concentrations well below the critical micelle concentration and it remains active at concentrations as high as 30 mM (1%). Neither activity is stimulated by cationic or nonionic detergents, or a variety of other agents, including trypsin. The purified tyrosinase is a glycoprotein having a polypeptide Mr = 175,000 by NaDodSO4-polyacrylamide gel electrophoresis. This monomeric species is enzymatically active in the presence of NaDodSO4. Detergent-activated tyrosinase has a KM for dihydroxyphenylalanine of 6 X 10(-4) M and a KM for tyrosine of 4 X 10(-4) M. Both activities are inhibited by copper chelators but not by an iron chelator. Further characterization of the detergent activation of this enzyme is presented in a companion paper (Wittenberg, C., and Triplett, E. L. (1985) J. Biol. Chem. 260, 12542-12546).
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PMID:A detergent-activated tyrosinase from Xenopus laevis. I. Purification and partial characterization. 393 Apr 97

We have found that glucosamine (1 mg/ml) or tunicamycin (0.2-0.4 micrograms/ml), specific inhibitors of lipid carrier-dependent glycosylation of protein, when added to cultured B-16 melanoma cells produce a marked loss of pigmentation, accompanied by distinctive biochemical as well as ultrastructural aberrations in their melanogenic compartments. Electron microscopic analysis shows that these newly induced unpigmented cells form uniquely altered melanosomes containing little or no melanin, although their population is not substantially reduced. Within the melanogenic compartments, selective aberration of melanosomes is seen, that is, deformity, bulging, and segregation of their interior membrane, as well as the intramelanosomal formation of irregularly concentric lamellar structure. No apparent structural deformity of Golgi apparatus, Golgi-associated endoplasmic reticulum of lysosome (GERL), and coated vesicles has been observed. Further, no substantial alteration is seen in mitochondria or other cellular structures. Quantitative analysis of altered and nonaltered melanosomes has revealed that the ratio of altered premelanosomes to the total number increases to 44% in glucosamine-treated cells and to 99.5% in tunicamycin-treated cels. Compared to 13% in the control. Electron microscopic dopa reaction has also revealed that these altered melanosomes seem to exhibit a weakly positive or a negative dopa reaction in both glucosamine- and tunicamycin-treated melanoma cells although a number of dopa-positive altered melanosomes are still seen. However, GERL and coated vesicles show no apparent decrease in dopa reaction. It may be concluded that glycoprotein synthesis is integral to the formation of normal melanosomes and to their specific melanizing function, which could be impaired by inhibition of the synthesis of asparagin-linked mannose-containing sugar chains. This results in retrogressive changes in the premelanosomal tyrosinase during its maturation process.
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PMID:Selective aberration and pigment loss in melanosomes of malignant melanoma cells in vitro by glycosylation inhibitors: premelanosomes as glycoprotein. 640 69

Tyrosinase (EC 1.14.18.1) was purified from regenerating chicken feathers. Most of the enzyme activity was in the insoluble fraction, which was solubilized with 0.5% sodium cholate. Solubilized tyrosinase showed multiple forms on isoelectric focusing. The isoelectric points had the following pI values: 5.06, 4.83, 4.68, 4.56, 4.44, 4.32, 4.24, 4.14, 4.06 and 3.97. This tyrosinase fraction was subjected to trypsin (EC 3.4.21.4) cleavage, Sephacryl S-200, hydroxylapatite and DEAE-cellulose chromatography. Purified enzymatically active tyrosinase also showed multiple forms. Their isoelectric points were: 4.23, 4.14, 4.06, 3.99 and 3.91. Each active form had almost the same molecular weight, estimated at 66 000. Staining for 1,2-diol groups of glycoproteins and neuraminidase (EC 3.2.1.18) treatment suggested that chicken tyrosinase is a glycoprotein. The enzyme showed both dopa(L-3,4-dihydroxylphenylalanine) oxidase activity and tyrosine hydroxylase activity.
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PMID:Purification and isoelectric heterogeneity of chicken tyrosinase. 643 56

A small gel electrophoretic system has been developed for the study of tryosinase from human hairbulb melanocytes. Enzyme is released from the hairbulb with Triton X-100. Electrophoresis is run in 60 mm microcapillary pipettes with an internal diameter of 1.5 mm. With this technique, tyrosinase from normally pigmented brown, black, blond, and red hairbulbs gives a single band when the gel is stained with L-dopa for enzyme activity. Tryosinase from tryosinase-positive oculocutaneous albino and Hermansky-Pudlak syndrome hairbulbs gives a single L-dopa band. Neuraminidase pretreatment of the tyrosinase from normal and albino hairbulbs changes the migration of the tyrosinase band to a less anodal position. Trypsin pretreatment has no effect. We conclude that human hairbulb tyrosinase is a glycoprotein and that tyrosinase-positive albino tyrosinase has no major electrophoretic difference from normal enzyme.
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PMID:Electrophoretic pattern of human hairbulb tyrosinase. 679 92

Human malignant melanoma cell lines have been divided into three broad groups on the basis of morphology, pigmentation, tyrosinase levels, the 2-dimensional electrophoretic patterns of their [3H]glucosamine-labeled glycoproteins and the presence or absence of an extracellular matrix of fibronectin. The most pigmented cell lines were characterized by the synthesis of a novel glycoprotein with a molecular weight of 75,000 and the absence of a fibronectin matrix. As cultured skin melanocytes also had these characteristics, this group of melanomas appears to be the most differentiated. Melanoma cell lines in the amelanotic group were characterized by the synthesis of high levels of HLA-DR antigen and by the production of an extracellular fibronectin matrix.
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PMID:Glycoproteins as differentiation markers in human malignant melanoma and melanocytes. 685 May 92

Proteins mapping at different loci are involved in melanogenesis and share several characteristic structural features (b locus, c locus, and slaty locus products). We describe a method to produce specific antibodies against human tyrosinase, the product of the c locus. Mouse L cells transfected with a human tyrosinase cDNA were used to generate antibodies by immunization of syngeneic C3H mice. These antibodies were able to precipitate the tyrosinase glycoprotein from both melanocytic cells and transfectants expressing tyrosinase. In contrast, transfectants expressing the related but distinct b locus protein (gp75 or TRP-1) did not react with these antibodies. In most cases, tyrosinase enzymatic activity could be precipitated and recovered in immune complexes, but one antibody response blocked tyrosinase activity. Immunostaining with anti-tyrosinase antibodies revealed an intracellular granular pattern in tyrosinase transfectants and melanocytic cells, but not transfectants expressing the b locus protein. This approach provides a general method to produce specific antibodies against tyrosinase, other members of the tyrosinase family of proteins, and potentially any other differentiation antigen.
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PMID:Production and characterization of antibodies against human tyrosinase. 750 35

The structural and functional integrity of cytoplasmic organelles is maintained by intracellular mechanisms that sort and target newly synthesized proteins to their appropriate cellular locations. In melanocytic cells, melanin pigment is synthesized in specialized organelles, melanosomes. A family of melanocyte-specific proteins, known as tyrosinase-related proteins that regulate melanin pigment synthesis, is localized to the melanosomal membrane. The human brown locus protein, tyrosinase-related protein-1 or gp75, is the most abundant glycoprotein in melanocytic cells, and is a prototype for melanosomal membrane proteins. To investigate the signals that allow intracellular retention and sorting of glycoprotein (gp)75, we constructed protein chimeras containing the amino-terminal extracellular domain of the T lymphocyte surface protein CD8, and transmembrane and cytoplasmic domains of gp75. In fibroblast transfectants, chimeric CD8 molecules containing the 36-amino acid cytoplasmic domain of gp75 were retained in cytoplasmic organelles. Signals in the gp75 cytoplasmic tail alone, were sufficient for intracellular retention and targeting of the chimeric proteins to the endosomal/lysosomal compartment. Analysis of subcellular localization of carboxy-terminal deletion mutants of gp75 and the CD8/gp75 chimeras showed that deletion of up amino acids from the gp75 carboxyl terminus did not affect intracellular retention and sorting, whereas both gp75 and CD8/gp75 mutants lacking the carboxyl-terminal 27 amino acids were transported to the cell surface. This region contains the amino acid sequence, asn-gln-pro-leu-leu-thr, and this hexapeptide is conserved among other melanosomal proteins. Further evidence showed that this hexapeptide sequence is necessary for intracellular sorting of gp75 in melanocytic cells, and suggested that a signal for sorting melanosomal proteins along the endosomal/lysosomal pathway lies within this sequence. These data provide evidence for common signals for intracellular sorting of melanosomal and lysosomal proteins, and support the notion that lysosomes and melanosomes share a common endosomal pathway of biogenesis.
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PMID:Intracellular sorting and targeting of melanosomal membrane proteins: identification of signals for sorting of the human brown locus protein, gp75. 764 99


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