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)

A pigmented subclone of Cloudman S91 melanoma cells, PS1-wild type, can grow in medium lacking tyrosine. This ability is conferred by phenylalanine hydroxylase activity, and not by tryptophan hydroxylase, tyrosine hydroxylase or tyrosinase activities, although the latter activity is also present in these cells. Conversion of phenylalanine to tyrosine was measured in living cells by chromatographic identification of the metabolites of [14C]phenylalanine and in cell extracts using a sensitive assay for phenylalanine hydroxylase. Phenylalanine hydroxylase activity in melanoma cell extracts was identified by its inhibition with p-chlorophenylalanine and not with 6-fluorotryptophan, 3-iodotyrosine, phenylthiourea, tyrosine or tryptophan; and by adsorption with antiserum prepared against purified rat liver phenylalanine hydroxylase, and migration of immunoprecipitable activity with authentic phenylalanine hydroxylase subunits in sodium dodecyl sulfate-polyacrylamide gel electrophoresis.
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PMID:Phenylalanine hydroxylase in melanoma cells. 2 86

Tyrosinase activity decreases as the reaction proceeds and is inhibited by L-3,4-dihydroxyphenylalanine oxidation products. Indole and tryptophan inhibit tyrosinase reaction and bovine albumin protects against end-product(s) inhibition or inactivation. Since the same tyrosinase reaction products are indole compounds and some authors reported the binding of indole derivatives with albumin, it is here suggested that indole intermediates of melanin synthesis inhibit or inactivate tyrosinase.
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PMID:Inhibition of tyrosinase by indole compounds and reaction products. Protection by albumin. 11 28

Tryptophan pyrrolase, a microsomal enzyme responsible for the break-down of tryptophan, has been detected in Bufo melanostictus. The enzyme has been found to be deactivated under influence of antivitiligo drug psoralene and activated by hydroquinone, an inhibitor of tyrosinase. Tryptophan pyrrolase has been found to have an antagonistic relationship with tyrosinase in Bufo melanostictus. The implication of the results has been discussed in relation to melanogenesis in vitiligo.
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PMID:Interrelationship of tryptophan pyrrolase with tyrosinase in melanogenesis of Bufo melanostictus. 41 23

The aim of this article is to emphasize the important role that copper plays in the function of nerve cells. We are reporting preliminary data which suggest that the swelling of axons which we produce in rats by iminodipropionitrile, IDPN, is due to its chelating action on copper, and how conversely supplementation with copper abolishes both symptoms and lesions. The copper values we obtained by atomic absorption spectrophotometry of the spinal cord and brain from the animals fully support this contention. In comparing these results with the diseases that are known to be due to copper deficiency, namely Menkes disease in man, swayback in lambs and several neurological mutant mice, we find not only similar axonal swellings, but also amelioration of symptoms and lesions by early administration of copper. Considering the main forms in which copper is present, we discuss the cuproproteins, i.e. ceruloplasmin and metallothionein, and their role in transport and delivery of copper to various organs. Further, the many cuproenzymes i.e. superoxide dismutase, tryptophan-2,3-dioxygenase, lysine oxidase, cytochrome oxidase, monoamine oxidases, tyrosinase, dopamine-beta-hydroxylase and d-amino levulinate dehydratase are noted for their roles in the nervous system. Finally, we suggest that neuronal copper deficiency should be more fully investigated as a possible etiological factor in the more common neurodegenerative diseases, such as Alzheimer's disease and amyotrophic lateral sclerosis, ALS.
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PMID:Deficiency of copper can cause neuronal degeneration. 161 61

We describe results demonstrating the positive regulation of melanogenesis by two substrates of the melanogenic pathway. We have found that L-tyrosine and L-dihydroxyphenylalanine (L-dopa), whose metabolic fates are affected by the activity of that pathway, can also act as its regulators. In living pigment cells, tyrosinase (EC 1.14.18.1), a crucial and rate-limiting enzyme of melanogenesis, acts in subcellular organelles known as melanosomes. Melanin is laid down only in these organelles. We demonstrate that supplementing Ham's F-10 medium with additional L-tyrosine or L-dopa during the culture of amelanotic Bomirski hamster melanoma cells results in a rapid increase in melanin formation, which is not simply due to greater availability of substrate. There is a rapid increase in tyrosinase activity and a large scale synthesis of melanosomes. The effects of L-tyrosine and L-dopa are prevented by the addition of cycloheximide. The actions of L-tyrosine and L-dopa are specific in that under similar conditions D-tyrosine, D-dopa, N-acetyl-L-tyrosine, L-phenylalanine, L-tryptophan and L-valine have little or no effect. The two substrates, L-tyrosine and L-dopa, appear to act through related but distinct mechanisms. Our findings provide an example of a little-known phenomenon: regulation of a differentiated eukaryotic phenotype through positive control by substrates in the pathway.
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PMID:Positive regulation of melanin pigmentation by two key substrates of the melanogenic pathway, L-tyrosine and L-dopa. 314 38

The structural investigation of four bio- and synthetic melanins, obtained by the action of polyphenol oxidase from potatoes and Psalliota campestris mushrooms and of tyrosinase from Sepia officinalis on tryptophan, or by means of performic oxidation, has been carried out by thermal decomposition performed in the ion source of a mass spectrometer. The structural characterization of the ionic species [C8H7ON](+.), common and abundant for all the examined compounds, has been obtained by accurate mass measurements and collisional spectroscopy. These mass spectrometric techniques have shown unequivocally for ionic species [C8H7ON](+.) the structure of 2-indolinone.
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PMID:Collisional spectroscopy in structural characterization of melanins: I. A first study on [C8H7ON](+.) ions originating from pyrolysis of biosynthetic and synthetic tryptophan melanins. 350 69

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

The stability of tryptophan was evaluated in several different food model systems using a chemical method (high pressure liquid chromatography after alkaline-hydrolysis) and rat assays. Losses of tryptophan were compared with the losses of lysine and methionine. Whey proteins stored in the presence of oxidizing lipids showed large losses of lysine and extensive methionine oxidation but only minor losses of tryptophan as measured chemically. The observed decrease in bioavailable tryptophan was explained by a lower protein digestibility. Casein treated with hydrogen peroxide to oxidize all methionine to methionine sulphoxide showed a 9% loss in bioavailable tryptophan. When casein was reacted with caffeic acid at pH 7 in the presence of monophenol monooxygenase (tyrosinase; EC 1.14.18.1), no chemical loss of tryptophan occurred, although fluorodinitrobenzene-reactive lysine fell by 23%. Tryptophan bioavailability fell 15%, partly due to an 8% reduction in protein digestibility. Alkali-treated casein (0.15 M-sodium hydroxide, 80 degrees, 4 h) did not support rat growth. Chemically-determined tryptophan, available tryptophan and true nitrogen digestibility fell 10, 46 and 23% respectively. Racemization of tryptophan was found to be 10% (D/(D+L)). In whole-milk powder, which had undergone "early' or "advanced' Maillard reactions, tryptophan, determined chemically or in rat assays, was virtually unchanged. Extensive lysine losses occurred. It was concluded that losses of tryptophan during food processing and storage are small and of only minor nutritional importance, especially when compared with much larger losses of lysine and the more extensive oxidation of methionine.
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PMID:Stability of tryptophan during food processing and storage. 1. Comparative losses of tryptophan, lysine and methionine in different model systems. 393 49

Some structural properties of Neurospora tyrosinase have been studied by fluorescence spectroscopy. The emission spectra observed for oxy-, deoxy-, met- and apo-tyrosinase and the Co2+-substituted form are indicative of a protein containing buried tryptophan residues. By using acrylamide and iodide, part of the emission is quenched, indicating heterogeneity in the tryptophan environment. Upon binding of Cu2+ or Co2+ to apo-tyrosinase, a marked decrease of the tryptophan quantum yield is observed. A further decrease in emission intensity results from the binding of molecular O2 to the deoxy form. The fluorescent probe 8-anilinonaphthalene-1-sulphonate binds to tyrosinase only when the metal ions are removed. Reconstitution of apo-tyrosinase with Cu2+ completely displaces the probe, suggesting that 8-anilinonaphthalene-1-sulphonate binds to apo-tyrosinase at the active site. The fluorescence properties of Neurospora tyrosinase are compared with those of haemocyanin.
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PMID:Fluorescence properties of Neurospora tyrosinase. 621 31

A comparison of the serum tyrosine, DOPA, tryptophan, tyrosinase and tryptophan pyrrolase levels of vitiliginous patients with those of normal subjects show abnormalities in all these parameters. As the clinical diagnosis of vitiligo may be made without difficulty, these parameters appear to be of little diagnostic value in vitiligo. But they may be considered as additional biochemical parameters in vitiligo.
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PMID:Abnormal tryptophan pyrrolase and amino acids related to melanogenesis in vitiligo. 640 73


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