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)

The chemical and enzymatic browning reactions of plant polyphenols and their effects on amino acids and proteins are reviewed. A model system of casein and oxidizing caffeic acid has been studied in more detail. The effects of pH, time, caffeic acid level and the presence or not of tyrosinase on the decrease of FDNB-reactive lysine are described. The chemical loss of lysine, methionine and tryptophan and the change in the bioavailability of these amino acids to rats has been evaluated in two systems: pH 7.0 with tyrosinase and pH 10.0 without tyrosinase. At pH 10.0, reactive lysine was more reduced. At pH 7.0 plus tyrosinase methionine was more extensively oxidized to its sulphoxide. Tryptophan was not chemically reduced under either condition. At pH 10.0 there was a decrease in the protein digestibility which was responsible for a corresponding reduction in tryptophan availability and partly responsible for lower methionine availability. Metabolic transit of casein labelled with tritiated lysine treated under the same conditions indicated that the lower lysine availability in rats was due to a lower digestibility of the lysine-caffeoquinone complexes.
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PMID:Nutritional consequences of the reactions between proteins and oxidized polyphenolic acids. 649 20

1. Frog epidermis tyrosinase was coupled to Sepharose activated with low concentrations of CNBr. The tetrameric form of the enzyme was linked to the matrix via its subunits. Dissociation of the bound active enzyme with guanidinium chloride yielded an active immobilized dimeric derivative. 2. Immobilized dimeric derivative was able to interact with soluble subunits formed transiently during renaturation. An 85% recovery of the native dopa oxidase specific activity was achieved after hybridization. 3. Fluorescence spectra of different immobilized derivatives suggested that tryptophan residues were involved in the interactions between tyrosinase subunits. 4. It is suggested that the activation of the subunits of tyrosinase involves a conformational change towards a more unfolded state, which favours a reassociation to the dimeric active state.
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PMID:Subunit interactions in tyrosinase from frog epidermis in immobilized enzyme systems. 679 71

We have successfully expressed the active tyrosinase of Streptomyces antibioticus in Escherichia coli under the control of the trp promoter by fusing the sequence to the ORF438 gene. Because our attempt to connect the polycistronic gene of ORF438 and tyrosinase directly to the trp promoter of E. coli resulted in the expression of functionally inactive tyrosinase, we decided to fuse the COOH-terminus of ubiquitin sequence to the NH2-terminus of ORF438. Ubiquitin fusion has been shown to augment the yield of cloned gene products in E. coli by increasing the stability or translational efficiency of the fusion proteins. As a result, E. coli transformants harboring a plasmid pTRUBF that contains the ubiquitin-fused ORF438 and the tyrosinase gene produced the strong black pigment of melanin. About 300 units of tyrosinase per liter of batch culture were detected when cultivated in M9 medium containing casamino acids, L-tyrosine, and copper supplements. The black pigment, however, was not seen when grown in LB medium, suggesting that the trp promoter is well regulated. When recombinant E. coli cells grown in LB medium were transferred to a tryptophan-deficient minimal medium with phenol, we observed that phenol was removed from the solution, and the color of the medium turned black. This is due to the fact that the tyrosinase has polyphenol oxidase properties. We expect to use this recombinant E. coli for the waste treatment of phenolic compounds.
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PMID:Tyrosinase production in recombinant E. coli containing trp promoter and ubiquitin sequence. 801 Jun 80

1. Tryptophan has been shown to inhibit dopa-oxidation by melanosomal tyrosinase. 2. The inhibition is of mixed-type with Ki = 1.6 x 10(-3) M. 3. Tryptophan does not interact with the oxidation product of the dopa-oxidase reaction. 4. Neither oxygen nor hydroxyl radicals are involved in the inhibition found in presence of tryptophan. 5. Tryptophan, like dopa, also inhibits tyrosine hydroxylase and dopa-oxidase activity of melanosomal tyrosinase and its inhibitory mechanism differs from inhibition due to non-substrate type compounds like cysteine, ascorbic acid. 6. These experiments together with previous findings suggest that the status of tryptophan may be similar to that of dopa in relation to regulation of melanogenesis.
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PMID:The effect of tryptophan on dopa-oxidation by melanosomal tyrosinase. 822 74

Since the etiology of vitiligo is still unknown, we searched for some abnormal biochemical parameters, if any, in subjects with vitiligo. Higher urinary excretion of indole metabolites in vitiliginous patients have been noted, in association with higher dioxygenase, superoxide dismutase, and tyrosine aminotransferase activity in their serum. Similar results have also been found in an animal model, Bufo melanostictus, during induced tyrosinase inhibition. Treatment with psoralen can reverse the parameters, except tyrosine aminotransferase, to a normal level. Although psoralens are not the magic bullet for the therapy of vitiligo, they are still being used as a chemotherapeutic agent against vitiligo on a major scale to date. Tryptophan was found to participate in the pathway of melanogenesis, as a precursor as well as a positive regulator of tyrosinase. Its behavior in this regard is much more similar to the conventional substrates tyrosine and dopa (dihydroxyphenylalanine). In consideration of combined participation of tyrosine and tryptophan in the synthesis of melanin and its breakdown, the possible influence of different enzymatic reactions, like mono-oxygenase, dioxygenase, and deamination, has been suggested.
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PMID:Vitiligo, psoralen, and melanogenesis: some observations and understanding. 888 9

We compared tyrosinase cDNA sequences from a line of autosomal albino and Black Silky chickens isolated from cultured melanocytes by reverse transcription-polymerase chain reaction (RT-PCR). Both sources produce a single DNA fragment of predicted normal tyrosinase size. Direct sequencing of the PCR product showed three mutated sites in the tyrosinase gene of the albino chicken. Two silent point mutations and a deletion of six nucleotides (-deltaGACTGG) at 817 bp in the tyrosinase cDNA sequence were observed when compared with the White Leghorn and Black Silky cDNA sequences. The deduced albino chicken tyrosinase protein lacks two amino acids, aspartic acid and tryptophan. The position of these amino acids is consistent with one of the potential copper-binding sites that should be indispensable for function of the enzyme. We speculate that the six-base deletion is responsible for the inactive tyrosinase in this line of albino chickens.
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PMID:Autosomal albino chicken mutation (ca/ca) deletes hexanucleotide (-deltaGACTGG817) at a copper-binding site of the tyrosinase gene. 1068 88

Tryptophan hydroxylase (TPH) is the initial and rate-limiting enzyme in serotonin biosynthesis. The enzyme activity is dependent on molecular oxygen, a tetrahydropterin cosubstrate, and ferrous iron. The present study demonstrates that TPH is inhibited by a novel compound, p-ethynylphenylalanine (pEPA), produced by the Heck reaction of trimethylsilylacetylene with N-tertbutyloxycarbonyl-4-iodo-L-phenylalanine methyl ester. pEPA is a more potent and specific inhibitor of TPH than p-chlorophenylalanine (pCPA). In the present study, pEPA was demonstrated to inhibit competitively and reversibly TPH in vitro (Ki = 32.6 +/- 6.2 microM vs. tryptophan). pEPA displayed little inhibitory activity toward tyrosine hydroxylase (EC 1.14.16.2), the initial and rate-limiting enzyme for catecholamine biosynthesis, and no inhibition of phenylalanine hydroxylase or tyrosinase. In addition, pEPA was a poor ligand for the serotonin transporter and several serotonin receptors. Administration of pEPA (30 mg/kg) to rats produced a 95 +/- 5% decrease in TPH activity in brain homogenates and a concomitant decrease in serotonin and 5-hydroxyindole-3-acetic acid levels (85%) at 24 h after injection. In contrast, pCPA produced a similar effect (87 +/- 5% decrease in TPH activity) only at 10 times the concentration (300 mg/kg). These results suggest that pEPA is a selective, reversible, and potent inhibitor of TPH both in vitro and in vivo. The potential for pEPA to inhibit selectively and reversibly the biosynthesis of serotonin may contribute to the characterization of the role of serotonin in behavioral and physiological activities.
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PMID:p-ethynylphenylalanine: a potent inhibitor of tryptophan hydroxylase. 1080 Sep 50

In the human epidermis both keratinocytes and melanocytes express POMC m-RNA. Immunohistochemical studies of both cell types demonstrate significantly higher levels of alpha-MSH in melanocytes than in keratinocytes. Both cell types also hold the full capacity for de novo synthesis/recycling of the essential cofactor (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin (6BH4). 6BH4 is critical for the hydroxylation of the aromatic amino acids L-phenylalanine, L-tyrosine, and L-tryptophan, for nitric oxide production and in various immune modulatory processes. Recently it was shown that tyrosinase activity is regulated by 6BH4 through a specific allosteric inhibition. The tyrosinase/6BH4 inhibition can be activated by 1:1 complex formation between 6BH4 and alpha-MSH, but an excess of alpha-MSH over 6BH4 can inhibit tyrosinase due to complex formation by tyr2 in the alpha-MSH sequence. In both melanocytes and keratinocytes 6BH4 controls the L-tyrosine supply via phenylalanine hydroxylase (PAH). Recently we were able to show that the cellular uptake of L-phenylalanine and its intracellular turnover to L-tyrosine is crucial for melanogenesis. alpha-MSH can promote the production of L-tyrosine via PAH due to activation of the PAH tetramer to the more active dimer by removing 6BH4 from the regulatory binding domain on the enzyme. In conclusion, alpha-MSH can control (1) intracellular L-tyrosine formation from L-phenylalanine in both melanocytes and keratinocytes, and (2) tyrosinase activity, directly, in melanocytes.
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PMID:alpha-MSH can control the essential cofactor 6-tetrahydrobiopterin in melanogenesis. 1081 64

3-Hydroxykynurenine is a tryptophan metabolite with an o-aminophenol structure. It is both a tyrosinase activator and a substrate, reducing the lag phase, stimulating the monophenolase activity, and being oxidized to xanthommatin. In the early stage of monophenol hydroxylation, catechol accumulation takes place, whereas 3-hydroxykynurenine is substantially unchanged and no significant amounts of the o-quinone are produced. These results suggest an activating action of 3-hydroxykynurenine toward o-hydroxylation of monophenols. 3-Hydroxykynurenine could therefore well act as a physiological device to control phenolics metabolism to catechols and quinonoids.
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PMID:3-hydroxykynurenine as a substrate/activator for mushroom tyrosinase. 1266 92

1. Ovarian tissue from Bombyx mori L. larvae about to pupate was cultured in Trager's (1935) salt solution and 10 per cent hemolymph, with indifferent results. Improvement of cultures was sought by modifying the culture medium. 2. To reduce the activity of the tyrosinase, hemolymph for culture medium was heated for 5 minutes at 60 degrees C., and the coagulated protein removed. 3. A physiological solution was formulated containing cations and amino acids as they occur normally in silkworm hemolymph. In both hanging-drop and small tube cultures use of this medium brought about increased cell number, improved cell appearance, more rapid mitoses, and longer life of cultures. 4. To the solution formulated from analyses, tryptophan, cystine, cysteine, malate, fumarate, succinate, and alpha-ketoglutarate were added after testing individually, resulting in improved growth in cultures. 5. Use of a silkworm egg extract prepared 4 to 5 days after acid treatment produced an increase in cell number. 6. In small roller tube cultures, when the new medium was changed twice a week, the cells spread over the walls of the tube in 4 or 5 days (Figs. 8 and 9), rapid mitoses were observed after 2 weeks, and transparent active cells were present at 3 weeks. Subculturing was not attempted.
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PMID:Culture in vitro of tissue from the silkworm, Bombyx mori L. 1334 39


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