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)

The antifungal reagent Fungizone (amphotericin B and deoxycholate) caused an activation in dopachrome tautomerase and dopa oxidase activities of B16/F10 melanoma cells at the routine concentration (2.5 micrograms/ml) used for preventing molds and yeast growth in cultures of animal cells. However, higher amphotericin B concentrations caused a significant cell death and the inhibition of enzymatic activities. At the optimal concentration of Fungizone, the enzymatic activities and melanin content were augmented as incubation time increased. The detergent sodium deoxycholate alone exerted no effect on these melanogenic parameters, eliminating the possibility that this detergent was partially responsible for melanogenic modifications produced by Fungizone. After withdrawal of Fungizone from the reaction medium, the recovery of melanogenic parameters to normal values was slower for DCT than for tyrosinase. The behavior of dopa oxidase was very similar to that reported by Johnson and Bagnara (Pigment Cell Res. 3, 173-175) for tyrosine hydroxylase.
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PMID:Effect of amphotericin B on dopachrome tautomerase activity and other melanogenic parameters in cultured B16/F10 melanoma cells. 149 75

In spite of the central role of tyrosinase in mammalian pigmentation, few data are available on its structure and structure-function relationships based on direct analysis of the protein. A number of reasons have been invoked to account for this situation, including the problems for its purification and its resistance to proteases. However, no study on the effects of proteases on purified tyrosinase has been reported. We have purified the melanosomal and cytosolic tyrosinases from B16 mouse melanoma and analyzed their susceptibility to trypsin digestion. Both isoforms are sensitive to trypsin, and display similar peptide maps and kinetics of proteolysis, suggesting that they are products of the same gene. The peptide maps and the kinetics of appearance of the fragments were consistent with the sequential removal of N-terminal peptides, leading to a core of 55.3 kDa for the melanosomal form and 48.6 kDa for the cytosolic enzyme. This core was apparently resistant to further proteolysis and catalytically inactive. The difference in molecular weight for the core of the cytosolic and melanosomal forms is the same as that calculated for the native isoforms. The kinetics of enzyme inactivation indicate that the tyrosine hydroxylase and Dopa oxidase activities of tyrosinase are lost at the same rate, and should therefore display similar if not identical structural requirements. The results are discussed in terms of the relationship of both isoforms and of the putative protein sequences deduced from the cDNA clones proposed for tyrosinase.
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PMID:Proteolysis with trypsin of mammalian tyrosinase isoforms from B16 mouse melanoma. 149 41

In C57 Bl-6 mice, melanogenesis is strictly coupled to the growth phase of the hair cycle (anagen). To further study this phenomenon of concerted developmental and pigmentary activity, we followed the sequence of tyrosinase (key enzyme of melanogenesis) expression and activity and the presence of the melanosomal protein gp 75 during the development of traumatically induced anagen follicles (days 0 = telogen, and days 1-12, after anagen induction studied). In addition to performing Northern and Western blots for tyrosinase, tyrosine hydroxylase activity (THA) and dopa oxidase activity (DOA) were measured. On day 0, DOA was undetectable, and THA was very low. On days 1 and 2, both activities were undetectable; starting from day 3, they increased rapidly, reaching a plateau on days 8 and 12. DO-positive proteins had apparent molecular weights (MW) of 66-68 kD (days 3-12), 72-74 kD (days 5-12), and 130 kD (days 8 and 12). Western blotting emphasized proteins of MW 66-68 kD (tyrosinase), and 73-75 kD (gp 75); tyrosinase was undetectable on day 0, but already present on days 1 and 2; it increased by day 5 and had reached a plateau on days 8 and 12; gp 75 was undetectable on days 0-2; it was present on day 3, increased by day 5, and reached a plateau on days 8 and 12. Northern blot analysis revealed high levels of tyrosinase mRNA on days 5 and 8, low levels on days 1-3, and none on day 0. These data suggest a highly regulated, time frame-restricted, differential pattern of tyrosinase transcription, translation, and enzyme activity during the different stages of the developing murine anagen follicle, possibly as a result of complex interactions between follicular melanocytes and their environment.
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PMID:Differential expression and activity of melanogenesis-related proteins during induced hair growth in mice. 167 5

New assays for the tyrosine hydroxylase and dopa oxidase activities of tyrosinase (EC 1.14.18.1) have been developed. The tyrosine hydroxylase assay uses L-[carboxy-14C]tyrosine as the substrate, 14CO2 is released from the products of the hydroxylation and further metabolism of L-[carboxy-14C]tyrosine by incubation with ferricyanide, and measured radiometrically. D-Dopa is a preferable cofactor to L-dopa for the assay. Dopa oxidase activity is measured spectrophotometrically. Dopaquinone, produced on the oxidation of L-dopa, reacts with Besthorn's hydrazone (3-methyl-2-benzothiazolinone hydrazone) to form a pink pigment with an absorbance maximum at 505 nm. Details of the optimisation of conditions for the assays and their specificities for the two enzyme activities are described.
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PMID:New assays for the tyrosine hydroxylase and dopa oxidase activities of tyrosinase. 167 12

3T3 Swiss mouse fibroblast cell lines expressing tyrosinase, the critical enzyme in melanin synthesis, have been established by co-transfection of a mouse tyrosinase cDNA and a G418-resistance gene. Of sixty-three clones isolated, four are brown in colour, presumably due to synthesis of melanin. Expression of both the tyrosine hydroxylase and dopa oxidase activities of tyrosinase by these pigmented clones has been demonstrated directly by enzyme assays. Electron microscopic studies suggest that the brown pigment is located in membrane-bound cytoplasmic vesicles.
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PMID:Expression of a mouse tyrosinase cDNA in 3T3 Swiss mouse fibroblasts. 190 37

Neuroblastomas are malignant childhood neoplasms that arise from derivatives of the neural crest. We report the characterization of a new neuroblastoma cell line, designated NBL-W, derived from the primary tumor of a patient with stage IVS disease (S. L. Cohn, C. V. Herst, H. S. Maurer, and S. T. Rosen, J. Clin. Oncol., 5: 1441-1444, 1987) according to the criteria of Evans [A. E. Evans, G. J. D'Angio, and J. Randolf, Cancer (Phila.), 27: 374-378, 1971]. Neurite-bearing (N) and substrate-adherent (S) cell lines have been subcloned from the parent line. N and S cells can interconvert, and both cell types label with the neural crest cell surface marker antibody, HNK-1. Cells in the subcloned lines and in the parent line have been shown by Southern blot analysis to contain approximately 100 copies of the N-myc gene. Cytogenetic analysis shows a homogeneously staining region present on chromosome 19. Although these subclones are of identical genotype, the S cells express lower amounts of N-myc mRNA and protein as compared to the N cells. N cells express several neuronal proteins including the neurotransmitter-processing enzymes tyrosine hydroxylase and dopamine beta-hydroxylase, the neuronal intermediate filament proteins peripherin and NF66/alpha-internexin, and the neural cell adhesion molecule. S cells generally lack neuronal markers but express the mesenchymal intermediate filament protein vimentin, and a small subset of the S cells express glial fibrillary acidic protein. Some S cells were labeled weakly with neural cell adhesion molecule antibody; others were negative. S cells did not express the glial marker S-100 or a melanocyte marker, tyrosinase. Thus, S cells express the neural crest marker HNK-1 but do not express a set of antigens characteristic of any known cell type derived from the neural crest. These results are consistent with the suggestion that differential N-myc expression may be involved in the interconversion of N and S cells but indicate that the S cell phenotype need not represent a highly differentiated neural crest derivative.
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PMID:Differential expression of N-myc in phenotypically distinct subclones of a human neuroblastoma cell line. 193 96

A suppression of norepinephrine, epinephrine, and its metabolites in malignant pheochromocytoma by metyrosine was associated with an increase in tyrosine, plasma DOPA, and sulfate esters of DOPA and dopamine, followed, with continuing metyrosine administration, by a further rise of both DOPA sulfate and dopamine sulfate. Urinary dopamine progressively increased in the course of metyrosine treatment, and this, along with the increase of the dopamine metabolite, dihydroxyphenylethanol, and plasma dopamine sulfate, occurred in the absence of any change in plasma dopamine. The octopamine metabolite para-hydroxyphenylglycol, which was initially elevated at least 10-fold, also increased after metyrosine treatment. The unexpected increase of DOPA (progressively more converted toward DOPA sulfate) in the presence of tyrosine hydroxylase inhibition and increase in tyrosine may result from channeling the excess tyrosine toward DOPA and melanin through tyrosinase. Increases in plasma dopamine sulfate and urinary dopamine suggest that dopamine sulfate may be generated via DOPA sulfate and urinary dopamine may originate from circulating DOPA. Tyrosine hydroxylase inhibition may thus result in DOPA generation in non-catecholamine-producing tissues by an alternative pathway. The resulting progressive increase in DOPA and its sulfate may lead to increased urinary dopamine. DOPA sulfate may be an alternative source of dopamine sulfate.
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PMID:Alternative catecholamine pathways after tyrosine hydroxylase inhibition in malignant pheochromocytoma. 196 15

At neutral (7.0) and slightly basic (8.2) pH, L-3,4-dihydroxyphenylalanine (L-DOPA), 3,4,5-trihydroxyphenylalanine (5-OH-DOPA) and 3,4-dihydroxyphenylethylamine (dopamine) undergo autoxidation. The binding of radiolabeled oxidation products of L-DOPA, 5-OH-DOPA and dopamine to membrane proteins was compared by a filtration procedure. Membranes from tentacles of the sea anemone Metridium senile bind significantly more 5-OH-DOPA than L-DOPA and dopamine. Membranes from rat brain and brains from the three-spined stickleback Gasterosteus aculeatus, bind significantly more dopamine than L-DOPA and 5-OH-DOPA. Membranes from Metridium contain an o-diphenol O2: oxidoreductase (tyrosinase). In the absence of inhibitors, enzymatic oxidation causes a fiftyfold increase in binding of L-DOPA and a more than tenfold increase in binding of dopamine, whereas the binding of 5-OH-DOPA only is increased by 10%. It is concluded than 5-OH-DOPA more easily undergo autoxidation than L-DOPA and dopamine, but its quinone form is probably less reactive with membrane proteins. The suitability of tyrosinase-mediated biosynthesis of L-DOPA and 5-OH-DOPA versus tyrosine hydroxylase-mediated biosynthesis of L-DOPA and dopamine in primitive nervous systems and in the vertebrate CNS is discussed on the basis of the cytotoxic potential through irreversible binding to membrane proteins of oxidation products of the catechol compounds formed.
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PMID:3,4-Dihydroxyphenylethylamine, L-3,4-dihydroxyphenylalanine and 3,4,5-trihydroxyphenylalanine: oxidation and binding to membranes. A comparative study of a neurotransmitter, a precursor and a neurotransmitter candidate in primitive nervous systems. 197 46

Tyrosinase activity was assayed in black and white human foreskin samples by measuring both the hydroxylation of tyrosine to dopa (tyrosine hydroxylase activity) and the conversion of [14C]tyrosine to [14C]melanin (melanin synthesis assay). Enzyme activity was found both in the particulate (75%) and soluble (25%) fractions of the cell. Membrane-bound tyrosinase was readily solubilized by either zwitter-ionic or nonionic detergents. The anionic detergent, sodium cholate, inhibited enzyme activity. Tyrosinase activity in black foreskin homogenates averaged almost three times that in white skin samples (33.8 pmols 3H2O/h/mg skin in black and 12.71 pmoles 3H2O/h/mg skin in white skin), although considerable overlap in activities existed among the two groups. Tyrosinase activities measured with two separate assays, tyrosine hydroxylase and [14C]melanin assays, were similar, suggesting that tyrosine hydroxylase activity is tightly coupled to melanin synthesis. Tyrosinase activity determined by either assay method generally correlated with skin melanin content. Kinetic analysis of tyrosinase from black and white foreskin revealed a Km for tyrosine of 2.5 X 10(-4) M in both skin types. Immunotitration experiments suggested that the difference in tyrosinase activities between white and black skin may be due, not only to different amounts of enzyme present in the melanocytes, but also possibly to differences in the catalytic activities of the enzyme found in melanocytes of black and white skin.
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PMID:The relationship between tyrosinase activity and skin color in human foreskins. 197 89

We compared tyrosinase activity (TH, DO, and native PAGE-defined isozymes) and melanin production in particulate and soluble fractions of hairbulb melanocytes of lethal yellow (Ay/a C/C), nonagouti black (a/a C/C), and albino (a/a c2J/c2J) of 3-, 6-, 9-, and 12-day regenerating hairbulbs. With respect to tyrosine hydroxylase (TH) and dopa oxidase (DO) activities, Ay/a melanocytes possessed only 25-35% of the activity of a/a; there were no genotype differences in either the subcellular distribution of activity in soluble and particulate fractions or in the relative increases of activity over the 12-day developmental period. TH data on wild-type agouti (AwJ/AwJ) mice over the 3-11 day regeneration interval showed an activity intermediate between that of a/a and Ay/a; the rate of TH increase reflected black and yellow phases of the agouti hair cycle. Analyses of the number and densities of dopa-sensitive bands following native PAGE of 3-, 6-, 9-, and 12-day hairbulb fractions of a/a and Ay/a mice suggested stage-dependent patterns. A comparison of rates and amounts of melanin production in 3-, 6-, 9-, and 12-day fractions showed consistent melanin production in Ay/a to be 10-20% that of a/a; however, fold increases in melanin production over the four stages were similar between genotypes. Overall, tyrosinase activity data support the notion that agouti locus modification of tyrosinase activity is a graded or quantitative rather than a qualitative phenomenon.
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PMID:Tyrosinase activity (TH, DO, PAGE-defined isozymes) and melanin production in regenerating hairbulb melanocytes of lethal yellow (Ay/a), black (a/a), agouti (AwJ/AwJ/) and albino (a/a/c2J/c2J) mice (C57BL/6J). 212 97


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