Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0025202 (melanoma)
 69,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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

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

The purification of two isoenzymes of tyrosinase has been carried out in Harding-Passey mouse melanoma. One is found in the cytosol and the other one bound to melanosomes. Both migrate as single bands on sodium dodecyl sulphate/polyacrylamide gels, having an apparent Mr of 58 000. Solubilized particulate tyrosinase showed an aggregation equilibrium involving a monomer, tetramer, octamer and a high-Mr micellar form with Brij 35, the solubilizing agent. H.p.l.c. studies indicated a interconversion between those species, the monomer contribution increasing with the sample dilution. The tetramer and the octamer probably represent the predominant forms in vivo. Soluble tyrosinase showed a simpler aggregation equilibrium, involving two forms, monomer and tetramer, with the same interconversion pattern. Fluorescence studies suggested that tryptophan residues were exposed to the aqueous environment when tyrosinase was dissociated by dilution. Tyrosinase shows a tendency to aggregate, at low protein concentration, and a resistance to dissociation by urea or SDS so remarkable that gel-permeation chromatography in 4M-urea does not affect the equilibrium, and the band obtained on SDS/polyacrylamide-gel electrophoresis is a dimer.
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PMID:Aggregation equilibria of tyrosinase of Harding-Passey mouse melanoma. 392 35

Epidemiological and experimental investigations have led to the hypothesis that the growth of malignant melanoma is induced by hormones. The demonstration of free-hormone binding sites in melanoma tissue may help to determine the validity of this hypothesis, as receptors are necessary for the transformation of hormonal action. The DCC assay with subsequent saturation analysis was used for the demonstration of specific cytoplasmatic binding sites of steroid hormones. The presence of free-cytosolic estrogen-, progesterone- and glucocorticosteroid receptors was investigated in 50 melanoma samples from 46 patients. In 20 of the 50 specimens, free estrogen and progesterone receptors were found. Free-glucocorticosteroid receptors we found in 10 cases. The use of four fold-labeled estradiol (2,4,6,7-[3]-17 beta-estradiol) in the DCC assay produced a false-positive demonstration of free-estrogen receptors. Tyrosinase hydroxylates estradiol at the C2 level of the steroid. Using fourfold labeled estradiol, tritium is separated at the C2 position, thus forming radioactive water in the cytosol which mimics high, free-estrogen binding sites. The use of twofold-labeled estradiol or L-dopa in the experiments with fourfold labeled estradiol produced no false-positive determinations of estrogen receptors. The demonstration of receptors in malignant melanomas was unaffected by the sex of the patient. Also, the type of malignant melanoma, the invasion level, and the prognostic index did not show a correlation with the presence of the various hormone receptors. In metastases, free steroid hormone receptors were detected less often than in the primary tumor.
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PMID:[Steroid receptors in malignant melanomas]. 393 Apr 22

The nature of the essential residues at the active site of Harding-Passey mouse melanoma tyrosinase has been explored by kinetic and photochemical modification studies. Km for L-dopa depends strongly on pH, so that acidic pH prevents the formation of the enzyme-substrate complex because the protonation of an enzyme group with a pKa of 6.6. Halide ions inhibit competitively the enzyme activity, being F the more potent one. This inhibition is also pH-dependent, showing the involvement of a protonatable group of the enzyme with apparent pKa ranging from 5.9 to 7.0. Tyrosinase has also been modified with visible light using Rose Bengal as photosensitizer, yielding a pH-dependent photoinactivation, characteristic of histidyl residues. All these results strongly support that histidine plays an important role in the dopa-oxidase activity of the enzyme, very probably acting as the ligand of copper at the active site of the enzyme.
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PMID:The involvement of histidine at the active site of Harding-Passey mouse melanoma tyrosinase. 393 27

Cholera toxin (choleragen) and melanocyte stimulating hormone alter within hours the morphology of melanoma cells in culture, and they slow the growth of serum-stimulated cells. After 7-10 days, cells exposed to choleragen or hormone show increased size and a fibroblastic growth pattern. Tyrosinase (EC 1.14.18.1; monophenol monooxygenase) activity increases after 3 days in the presence of 10(-8) M hormone or 10(-10) M choleragen. Binding studies with (125)I-labeled choleragen indicate that although a melanoma cell can bind a maximum of 10(6) molecules of cholera toxin, only about 4000 binding sites must be occupied to achieve maximum stimulation of tyrosinase activity. Melanocyte stimulating hormone and choleragen probably have different membrane-binding sites. After exposure to choleragen for 5 min, membrane adenylate cyclase (EC 4.6.1.1) activity increases dramatically upon further incubation of intact cells for several hours at 37 degrees and falls slowly to basal values over a period of more than 10 days. Hormone stimulation of adenylate cyclase is rapidly reversed by washing the cells, but subsequent restimulation of cyclase by the hormone is impaired. These studies indicate that cAMP mediates the effects of melanocyte stimulating hormone on growth and morphology as well as on tyrosinase activity. Cholera toxin may permanently activate the available adenylate cyclase molecules, and the protracted decay of stimulation that follows may reflect the biological turnover of adenylate cyclase molecules in these cells.
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PMID:Cholera toxin mimics melanocyte stimulating hormone in inducing differentiation in melanoma cells. 436 71

Tyrosinase activity in the soluble fraction of the cells and melanin content in the whole cells of the black-melanotic (Ma), brown-melanotic (MI) and amelanotic (Ab) hamster melanomas were studied. The activity of the soluble tyrosinase was highest in MI lower in Ma, and very low in Ab melanoma. Melanin content was greatest in the Ma, lower in MI, and none in Ab melanoma. Acrylamide gel electrophoretic pattern of the soluble tyrosinase consisted of 2 bands in Ma and MI melanomas, and of 1 band in Ab melanoma.
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PMID:Biochemical characterization of three hamster melanoma variants--I. Tyrosinase activity and melanin content. 642 36

Tyrosinase activity in the Ab hamster amelanotic melanoma cells cultured in serum-free Eagle's MEM increased 3 times after 6 h of primary cell culture. This increase was inhibited completely by cycloheximide, while actinomycin D had no effect on this process. After 24 h of culture in MEM with calf serum, further increase of the tyrosinase activity was inhibited by both cycloheximide and actinomycin D. The data presented may indicate that the increase of tyrosinase activity in the primary cell culture of the Ab melanoma is due initially to the unblocking of translation and later to the activation of transcription of the gene controlling the enzyme.
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PMID:Effects of actinomycin D and cycloheximide on the increase in tyrosinase activity of hamster amelanotic melanoma cells in vitro. 644 69

Tyrosinase in a melanosome is known to be inactivated during melanin formation in vivo, and a similar inactivation was observed in vitro when melanosomes isolated from Harding Passey mouse melanoma were incubated with dopa. Tyrosinase, whether particle bound or in soluble form, was inactivated during the dopa-tyrosinase reaction and the reduction rate of its activity was proportional to the reaction time. Tyrosinase inactivation also occurred when ascorbic acid was added to the reaction system; in which dopaquinone, an oxidation product of dopa which is immediately converted back to dopa by ascorbic acid thus preventing melanin formation. When 14C-dopa or 14C-ascorbic acid were added to the reaction mixture, these radioactive substances were not recovered from the inactivated enzyme protein fraction after incubation. In addition this inactivation of tyrosinase by dopa was not inhibited by any of: 1.4-diazabicyclo[2.2.2]octane, scavenger for singlet oxygen; D-mannitol, that for hydroxyl radical; superoxide dismutase, that for superoxide anion; and catalase, cleavaging enzyme for hydrogen peroxide. Thus the inactivation of tyrosinase appears to be due to neither these radicals, nor reaction products from dopa or ascorbic acid, but to changes in the enzyme itself.
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PMID:Inactivation of tyrosinase by dopa. 677 5


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