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)

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

When the Legionnaires' disease (LD) bacterium is grown on supplemented Mueller-Hinton agar, brown pigmentation of the medium occurs. Since this browning may result from tyrosinase-mediated formation of melanin, we supplemented yeast-extract agar with various aromatic precursors of melanin and inoculated it with eight strains of the LD bacterium. Browning occurred with growth of each LD strain of the bacterium on yeast-extract agar enriched with 2.5 mmol/L of L-phenylalanine or L-tyrosine but not without such enrichment. Equimolar D-phenylalanine or D-tryosine in yeast-extract agar did not enhance browning. The LD bacterium may possess L-phenylalanine hydroxylase activity, but it does not use D-aromatic amino acids effectively in pigment production.
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PMID:Aromatic substrate specificity of browning by cultures of the Legionnaires' disease bacterium. 10 39

The tyrosinase activity in two sucrose gradient isolated melanosome fractions from a melanotic hamster melanoma was found to increase after alpha-chymotrypsin treatment. The enhancement in tyrosinase activity had its maximum at a concentration of 1 mg/ml alpha-chymotrypsin after 120 min incubation at 37 degrees C. No direct activating effect of alpha-chymotrypsin was found either on the soluble tyrosinase fraction from freshly prepared untreaed whole-tumor homogenate or on purified mushroom tyrosinase. The activating effect of alpha-chymotrypsin upon the melanosome tyrosinase is believed to be due to the endopeptidic hydrolysis of the--CO--NH--bound existing between tyrosinase and tyrosine and phenylalanine residues in the melanin molecule. Although alternative interpretations are not excluded, the observed enhancement in tyrosinase activity after alpha-chymotrypsin treatment of melanosomes might indicate the existence of an "enzyme liberating" mechanism in the melanosomes.
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PMID:Chymotrypsin activation of melanosome tyrosinase in hamster melanotic melanoma. 11 73

alpha-Hydrazinophloretic acid, the hydrazino analogue of tyrosine, was shown to behave as a competitive inhibitor of tyrosinase. Some closely related compounds, especially the hydrazino analogue of phenylalanine as well as other hydrazine derivatives, will also inhibit the enzyme, but in these cases, the inhibition observed belonged to the non-competitive type.
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PMID:[Alpha-hydrazinophloretic acid, competitive inhibitor of fungal tyrosinase]. 40 26

Quassin, a mosquito larvicide isolated from Quassia amara, inhibits tyrosinase activity in the larvae of Culex quinquefasciatus. Since tyrosinase is directly involved in sclerotisation of the cuticle, it is suggested that quassin, as a larvicide, inhibits development of the cuticle. In presence of quassin phenylalanine, tyrosine and L-dopa levels were increased in larvae. In the larval stages, mosquitoes have a high concentration of phenylalanine and tyrosine with the level of the latter being very high just before pupation and then declines sharply. Monoamine oxidase (MAO), an enzyme directly involved in the metabolism of catecholamines, remained unaffected by quassin, in fact the level of adrenaline also remained unchanged in larvae during quassin poisoning. MAO showed high variation in its activity between synthetic and natural substrates. Tyramine is not a substrate for MAO. Tyrosinase activity was high in developing stages and negligibly low in adults and showed specificity to L-dopa. Phenylalanine and tyramine are unaffected by tyrosinase. Blood feeding did not influence the activity of both these enzymes.
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PMID:Effect of quassin on the metabolism of catecholamines in different life cycle stages of Culex quinquefasciatus. 142 64

Four fatty acid conjugates of a cyclic lactam-bridged alpha-MSH fragment analogue were synthesized and their potencies and biological activities compared in several melanotropin bioassays. Palmitoyl, myristoyl, decanoyl, and hexanoyl conjugates of H-Asp-His-D-Phe-Arg-Trp-Lys-NH2 were prepared. In the in vitro mouse melanoma cell assay, each of the conjugates was 10-100 times more potent than alpha-MSH or the substrate peptide in elevating tyrosinase activity. The shorter conjugates of hexanoic and decanoic acid were as potent as alpha-MSH in the lizard skin bioassay, whereas the longer myristoyl and palmitoyl analogues were about 100 times less potent. The potency of the myristoyl and palmitoyl conjugates increased with time in contact with the skins. These observations may be related to the more lipid-like nature of these peptide-fatty acid conjugates. Each of the conjugates exhibited prolonged melanotropic activity in the lizard skin bioassays and in the mouse S91 melanoma tyrosinase bioassay, since the biological response continued following removal of the conjugates from the incubation media. The prolonged residual melanotropic activity resulted from conjugation of the fatty acids to the MSH fragment analogue since the analogue itself did not exhibit prolonged activity.
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PMID:Synthesis and biological activities of fatty acid conjugates of a cyclic lactam alpha-melanotropin. 173 18

A new tyrosine-specific LC assay with pre-column fluorogenic derivatization is described for Tyr-Gly as model peptide. o-Hydroxylation of the tyrosine residue with tyrosinase in the presence of ascorbic acid, followed by oxidation to the corresponding quinone by potassium ferricyanide at room temperature and condensation with 1,2-diamino-1,2-diphenylethane in the presence of acetonitrile gave a highly fluorescent species. The resulting fluorescence signal was stable over the investigated period of 5 h and exhibited a linear response curve on a reversed-phase LC system. Under optimized reaction conditions, the lower limit of detection for Tyr-Gly was 200 fmol per injection. Examination of a series of dipeptides (L-Tyr-L-X; X = Gly, Ala, Val, Leu, Phe) showed no significant influence of neighbouring amino acids on the enzymatic hydroxylation by tyrosinase. This and the formation of a highly fluorescent signal for Leu-enkephalin suggests the general feasibility of the approach for the determination of tyrosine-containing peptides.
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PMID:A new fluorogenic assay for tyrosine-containing peptides. 181 76

As a part of an ongoing project aimed at developing new skin depigmenting agents, the ability of variously substituted 2-aryl-1,3-thiazolidines to inhibit melanogenesis in vitro was investigated. At 0.2 mM concentration 2-(2'-hydroxyphenyl)-1,3-thiazolidine-4-carboxylic acid (Th2), as well as the descarboxy analog (Th1) and, to a lower extent, the 4'-hydroxy isomer (Th3) all proved capable of preventing the tyrosinase catalyzed conversion of 0.2 mM L-tyrosine to melanin. Spectrophotometric monitoring of the reaction course in the presence of Th2 showed the initial formation of a yellow chromophore (lambda max 400 nm) which slowly decayed, being eventually replaced by a new absorption maximum centered at 305 nm. HPLC analysis of the final incubation mixture revealed the presence of a major product (lambda max 306 nm), ninhydrin and ferric chloride positive, which was isolated by gel filtration on Sephadex G-10 and was identified as beta-[7-(3-carboxy-5-hydroxy-3,4-dihydro-2H-1,4-benzothiazinyl)]al anine (DBA) by 1H-NMR spectroscopy. Attempts to isolate the intermediate with lambda max 400 nm were hampered by its marked instability under the usual chromatographic conditions. However, the nature of the chromophore, coupled with mechanistic considerations, suggested for the compound the Schiff base-containing structure 3,4-dihydroxy-5-S-(N-salicylidenecysteinyl)phenylalanine (salcysdopa). This was substantiated by: (i) the formation of a zinc complex (lambda max 349 nm) analogous to that observed with the model Schiff base N-salicylidene leucine; and (ii) detection by 1H-NMR of a Schiff base resonance at delta 8.1 during the yellow chromophoric phase of the reaction. It was concluded that 1,3-thiazolidines inhibit melanin formation by a mechanism that involves the trapping of enzymically generated dopaquinone by the -SH containing Schiff base arising by cleavage of the thiazolidine ring. The salcysdopa adduct thus formed undergoes hydrolysis and subsequent ring closure to give eventually the colorless DBA.
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PMID:2-Aryl-1,3-thiazolidines as masked sulfhydryl agents for inhibition of melanogenesis. 190 Dec 20

We have identified three different tyrosinase gene mutant alleles in four unrelated patients with type IB ("yellow") oculocutaneous albinism (OCA) and thus have demonstrated that type IB OCA is allelic to type IA (tyrosinase negative) OCA. In an inbred Amish kindred, type IB OCA results from homozygosity for a Pro----Leu substitution at codon 406. In the second family, type IB OCA results from compound heterozygosity for a type IA OCA allele (codon 81 Pro----Leu) and a novel type IB allele (codon 275 Val----Phe). In the third patient, type IB OCA results from compound heterozygosity for the same type IB allele (codon 275 Val----Phe) and a novel type IB OCA allele. In a fourth patient, type IB OCA results from compound heterozygosity for the codon 81 type IA OCA allele and a type IB allele that contains no identifiable abnormalities; dysfunction of this type IB allele apparently results from a mutation either well within one of the large introns or at some distance from the tyrosinase gene. In vitro expression of the Amish type IB allele in nonpigmented HeLa cells demonstrates that the Pro----Leu substitution at codon 406 greatly reduces but does not abolish tyrosinase enzymatic activity, a finding consistent with the clinical phenotype.
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PMID:Tyrosinase gene mutations associated with type IB ("yellow") oculocutaneous albinism. 190 91

Crosslinking of [14C]L-tyrosine to at least five hamster melanoma cell surface proteins is reported. This effect was abolished by addition of nonradioactive L-tyrosine, L-phenylalanine, or L-dopa, but not by D-tyrosine, tyramine, dopamine, norepinephrine, or epinephrine. The above proteins can be purified by tyrosine-affinity chromatography. They have molecular weights different from proteins staining for dopa oxidase and proteins that bind anti-tyrosinase antibody in Western blots. It is suggested that they may be a hithergo unrecognized part of the cellular apparatus governing melanogenesis.
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PMID:L-tyrosine-binding proteins on melanoma cells. 191 93


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