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 tapetum lucidum of the alligator gar Lepisosteus was shown by t.l.c. to contain a new phenolic amino acid, which is apparently a major constituent of the reflecting material. It was isolated in a yield of 0.5 mg/eye and its physical and chemical characteristics, especially reductive hydrolysis with hydriodic acid giving dopa (3,4-dihydroxyphenylalanine) and cysteine, suggested that it might to SS-dicysteinyldopa. Tyrosinase oxidation of L-dopa in the presence of an excess of L-cysteine yielded, in addition to known 5- and 2-S-cysteinyldopa, the same amino acid as that isolated from the eye of the gar, thus confirming the gross structure. The position of the two cysteine residues was established by the fact that tyrosinase oxidation of catechol and cyteine gave 3-S-cysteinylcatechol and 3,6-SS-dicysteinylcatechol. The natural amino acid is therefore formulated as 3-(2,5-SS-dicysteinyl-3,4-dihydroxyphenyl)alanine (2,5-SS-dicysteinyldopa), which may be formed by two consecutive additions of cysteine, first to dopaquinone and then to 5-S-cysteinyldopaquinone. The enzymic synthesis of 2,5-SS-dicysteinyldopa in vitro suggests that it may also be involved in the biosynthesis of phaeomelanin.
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PMID:A new amino acid, 3-(2,5-SS-dicysteinyl-3,4-dihydroxyphenyl)alanine, from the tapetum lucidum of the gar (Lepisosteidae) and its enzymic synthesis. 40 9

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

p-Coumaroyl-D-glucose hydroxylase in sweet potato (Ipomoea batatas Lam.) has been purified to apparent electrophoretic homogeneity using a combination of anion-and cation-exchange, hydrophobic and gel filtration chromatography. The purified enzyme was a monomer with a molecular weight of 33,000 and pI of 8.3. The purified enzyme showed not only hydroxylase activity but also polyphenol oxidase activity. L-Ascorbic acid was the best electron donor for the hydroxylation reaction, which had an optimum pH of 7.0. The enzyme hydroxylated p-coumaroyl-D-glucose, p-coumaric acid, and p-cresol but did not act on o-coumaric acid, m-coumaric acid, 4-hydroxy-3-methoxycinnamic acid, p-hydroxybenzoic acid or L-tyrosine. While the enzyme utilized p-coumaroyl-D-glucose and p-coumaric acid equally at pH 7.0, it hydroxylated only p-coumaroyl-D-glucose at pH 5.5. The enzyme oxidized diphenols such as D,L-(3,4-dihydroxyphenyl) alanine and caffeic acid, but exhibited no clear pH optimum in this reaction characteristic of polyphenol oxidase. Both the hydroxylase and the polyphenol oxidase activities were strongly inhibited by beta-mercaptoethanol, diethyldithiocarbamate, KCN, and p-coumaric acid (in concentrations higher than 5 mM). Ammonium sulfate and sodium chloride activated the hydroxylase activity but not the polyphenol oxidase activity of the enzyme. The enzyme activity and L-ascorbic acid contents changed in a manner suggesting their involvements in chlorogenic acid biosynthesis during incubation of sliced sweet potato root tissues.
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PMID:Purification and characterization of p-coumaroyl-D-glucose hydroxylase of sweet potato (Ipomoea batatas) roots. 198 92

A fast, simple and inexpensive enzymatic preparation of 3,4-dihydroxyphenyl-L-alanine (L-DOPA) from molecular oxygen and tyrosine using mushroom tyrosinase is described. The theoretical incubation time for production of [15O]L-DOPA with maximal specific activity from [15O]O2 can be calculated to be about 3 min. In practice, using a specially-designed glass reaction chamber to facilitate the incorporation of gaseous molecular oxygen into L-DOPA with zero lag-time, a 3 min reaction with 1% oxygen in nitrogen results in the formation of approx. 3.9 mumols of L-DOPA, representing conversion of about 14% of the tyrosine substrate. Given access to a supply of [15O]O2, the method should be applicable to the preparation of [15O]L-DOPA for use as a PET tracer.
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PMID:Fast enzymatic preparation of L-dopa from tyrosine and molecular oxygen: a potential method for preparing [15O]L-dopa. 217 94

A tyrosinase obtained from cultured human melanoma cells was found to oxygenate 2,4-dihydroxyphenylalanine to the strongly cytotoxic amino acid 6-hydroxydopa (2,4,5-trihydroxyphenylalanine). The oxygenation was dependent on the presence of a reducing co-substrate such as dopa or dopamine. The rate of oxygenation of 2,4-dihydroxyphenyl-D,L-alanine was similar to that of L-tyrosine, the normal substrate of tyrosinase. The enzymatic reaction demonstrated may prove of value in the chemotherapy of human melanoma.
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PMID:Production of 6-hydroxydopa by human tyrosinase. 240 19

Both native glue protein from marine mussels and a synthetic nonhydroxylated analog were analyzed by far-uv CD under a variety of conditions. Analysis of the CD spectra using various models strongly suggest a primarily random coil structure for both forms of the protein, a fact also supported by the absence of spectral change for the glue protein upon dilution into 6 M guanidine hydrochloride. The nonhydroxylated analog, which consists of 20 repeats of the peptide sequence Ala-Lys-Pro-Ser-Tyr-Pro-Pro-Thr-Tyr-Lys, was further characterized by enzyme modification using mushroom tyrosinase. Enzymatic hydroxylation of tyrosines was found to be best fit by a model containing two rate constants, 5.6 (+/- 0.6) X 10(-3) and 7.2 (+/- 0.3) X 10(-2) min-1. At equilibrium, HPLC analysis of digests showed nearly 100% conversion of Tyr-9 and only 15 to 35% conversion of Tyr-5. The Chou and Fasman rules for predicting structure were applied to the repeat sequence listed above. The rules predict the absence of alpha helix and beta pleated sheets in the structure of this peptide. On the other hand, beta turns are predicted to be present with Tyr-5 being in the region of highest probability. These data suggest that the protein in solution has only a small amount of secondary structure.
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PMID:Mussel glue protein has an open conformation. 249 14

This study pursued the isolation and partial characterization of the enzyme polyphenoloxidase from apple (Malus domestica Anna variety), grown in the Hermosillo Coast (State of Sonora, Mexico). The effects of pH and temperature as well as its specificity towards substrates, and its behavior under conditions of hydrophobic chromatography, were studied. The enzyme was isolated from a residual powder obtained from ripe apples homogenized with cold acetone. The extract thus prepared was used to characterize the enzyme, and it showed an optimum pH of 5.36 and an optimum temperature of 35 degrees C. The substrate specificity proved to decrease from 4-methyl catechol, chlorogenic acid, catechol, and caffeic acid, to 3,4-dihydroxiphenyl alanine (DOPA). The enzyme resulted to be more thermostable (temperature range: 35 degrees C to 60 degrees C) than the rest of oxidases of plant origin. When the extract was eluted under conditions of hydrophobic chromatography separation, it appeared as a single peak resulting in a 300 fold purification. The phenolase activity characteristics found in the present study were similar to those observed in other apples from temperate climates; however, this particular polyphenoloxidase is more thermostable under natural conditions. This explains why apples of the Anna variety, at the high harvesting temperature, show a very fast formation of brown spots even when there is a minor damage. The content of compounds with phenolic group was high (1.16 g/100 g fresh weight). Further increase of the velocity of fruit enzymatic browning was due to this reason.
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PMID:[Isolation and partial characterization of phenoloxidase from apples (Malus domestica, var. Anna)]. 251 28

Tyrosinase was isolated from cultured melanoma cells using a procedure involving solubilization of the enzyme by means of Triton X-100, followed by different types of chromatography and tryptic digestion to make the enzyme soluble even in the absence of detergent. Starting with a membranous material containing 72 mg protein, 0.21 mg tyrosinase was obtained. The recovery of tyrosinase was 36% of the quantity found in the membranous starting material. In order to acquire a completely purified enzyme preparation suitable for amino acid sequence analysis, SDS-PAGE followed by blotting onto a polyvinylidene difluoride membrane was performed as a final step. The apparent molecular weight was found to be 66,000. Determination of the amino acids of the aminoterminal portion by automated Edman degradation showed the following sequence: His-Phe-Pro-Arg-Ala-X-Val-Ser-Ser-Lys-Asn-Leu-Met-Glu-Lys-Glu-X-X-Pro-Pr o-The enzyme purified has an amino acid sequence identical with that of human tyrosinase deduced from c-DNA by Kwon et al. Striking similarities between our amino acid sequence and that predicted by Yamamoto et al. from mouse tyrosinase c-DNA were also observed.
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PMID:Isolation of human tyrosinase from cultured melanoma cells. 256 29

Free tyrosine and tyrosine residues in various peptides and proteins are converted into dopa and dopa residues by tyrosinase (monophenol,L-dopa:oxygen oxidoreductase, EC 1.14.18.1) in the presence of reductants. The efficiency of the tyrosine-to-dopa conversion was examined under varied conditions, such as the substrate-to-tyrosine ratio, concentrations of reductant and oxygen in the reaction solution, pH, temperature and reaction time. The highest dopa yields were achieved with the following optimal conditions for hydroxylation: 0.1 M phosphate buffer at pH 7, 25 mM ascorbic acid, 1 mM tyrosine, 50 micrograms/ml tyrosinase and 20 degrees C. Using these conditions, up to 70% of free tyrosine was converted into dopa, and tyrosine residues in several synthetic peptides were also hydroxylated to dopa residues at ratios as high as free tyrosine. The preparation of hydroxylated analogues of the decapeptide (Ala-Lys-Pro-Ser-Tyr-Pro-Pro-Thr-Tyr-Lys), in particular, may contribute to a better understanding of adhesion in the dopa-containing mussel glue protein.
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PMID:Optimization of hydroxylation of tyrosine and tyrosine-containing peptides by mushroom tyrosinase. 308 86

The cytotoxic activities of three new synthetic catechol analogues, beta-[(p-hydroxyphenyl)amino]alanine (Compound 1), N delta-(p-hydroxyphenyl)ornithine (Compound 2), and N delta-(m-hydroxyphenyl)ornithine (Compound 3), were determined against 10 human melanoma and 5 nonmelanoma cell lines. Activities of L-DOPA and 3,4-dihydroxybenzylamine were also measured. Dose-response curves were obtained and concentrations in micrograms/ml required to give 90% inhibition of colony formation (IC90) were calculated. Using a cutoff IC90 of less than 2.5 as a definition of activity. Compound 2 was active in 6 of 10 melanoma and 0 of 5 nonmelanoma cell lines while both Compound 1 and L-DOPA methyl ester were active in 1 of 10 melanomas and 0 of 5 nonmelanomas. Compound 3 was inactive in all cell lines and all IC90 values exceeded 100. 3,4-Dihydroxybenzylamine was active in 3 of 8 melanomas and 1 of 5 nonmelanomas. Regression analysis of IC90 values for Compound 2 and tyrosinase levels in the 15 cell lines yielded a correlation coefficient of 0.93 (P less than 0.001). By contrast, a similar analysis for 3,4-dihydroxybenzylamine gave a correlation coefficient of 0.17 (P greater than 0.05). Spectrophotometric data indicated that Compounds 1 and 2 were oxidized by tyrosinase to quinones. Cytotoxic activity was blocked by the tyrosinase inhibitor phenylthiocarbamide. Since the rates of activation of Compounds 1 and 2 were identical, the higher activity of Compound 2 was probably due to its higher lipophilicity and greater intracellular accumulation. Compounds 1 and 2 exhibited greater potency and selectivity against malignant melanoma than did the natural product L-DOPA methyl ester.
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PMID:Structure-activity relationships defining the cytotoxicity of catechol analogues against human malignant melanoma. 313 17


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