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)

5,6-Dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA), which are important intermediates in melanogenesis, can be converted into the corresponding melanin pigments by the action of the lipoxygenase/H2O2 system. Kinetic and HPLC analyses indicate that both DHI and DHICA are good substrates for this enzymatic system. Enzyme activity on both substrates was measured in comparison with peroxidase and tyrosinase; the oxidizing behaviour of lipoxygenase is more similar to that of peroxidase rather than that of tyrosinase. The antioxidant properties of DHI- and DHICA-melanins have been investigated in comparison with other kinds of melanins. DHICA-melanin shows a more pronounced antioxidant effect than that of DHI-melanin and this behaviour can be ascribed to the different structure and solubility of the two pigments. The mixed polymer synthesized from DHI and DHICA is the most effective one. Some implications about the possible explanation of the above mentioned behaviour are discussed.
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PMID:Lipoxygenase/H2O2-catalyzed oxidation of dihdroxyindoles: synthesis of melanin pigments and study of their antioxidant properties. 989 37

A crude enzyme extract from Dioscorea esculenta var. fasiculata tissue subjected to ion exchange chromatography on DEAE-Sephadex A-50 column. This procedure resolved the extract into two main protein peaks one of which eluted through the column relatively unbound while the other protein peak which remained bound to the column was eluted with 1.0 M NaCl. Both protein peaks contained polyphenol oxidase (PPO) and peroxidase (POD) activities. The non-binding protein peak was resolved by gel filtration on Sephadex G-200 into distinct PPO and POD activities and by virtue of their apparent molecular weights of 95.5 Kd and 38.0 Kd for PPO and POD respectively were determined to be the typical enzymes. The PPO activity was completely inhibited invitro by 5 mM polyvinyl pyrrolidone (PVP). The binding protein peak was not resolved by gel filtration. It contained PPO activity which was not inhibited by PVP and a POD activity which was completely inhibited by dithiothreitol (DTT) This ionic protein peak contained 60% of total POD in the tissue, has an apparent molecular weight of 56 Kd and is suggested to be a strongly anionic peroxidase which also exhibits polyphenol oxidase activity.
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PMID:Peroxidase-polyphenol oxidase association in Dioscorea esculenta. 993 63

Salivary homogenates of the adult female mosquito Anopheles albimanus have been shown previously to contain a vasodilatory activity associated with a catechol oxidase/peroxidase activity. We have now purified the salivary peroxidase using high-performance liquid chromatography. The pure enzyme is able to relax rabbit aortic rings pre-constricted with norepinephrine. The peroxidase has a relative molecular mass of 66 907 as estimated by mass spectrometry. Amino-terminal sequencing allowed us to design oligonucleotide probes for isolation of cDNA clones derived from the salivary gland mRNA from female mosquitoes. The full sequence of the cDNA demonstrated homology between A. albimanus salivary peroxidase and several members of the myeloperoxidase gene family. A close comparison of A. albimanus salivary peroxidase with canine myeloperoxidase, for which the crystal structure is known, showed that all six disulfide bridges were conserved and demonstrated identity for all five residues associated with a Ca2+-binding site. In addition, 16 of 26 residues shown to be in close proximity to the heme moiety in the canine myeloperoxidase were identical. We conclude that the salivary peroxidase of A. albimanus belongs to the myeloperoxidase gene family. Other possible functions for this molecule in blood feeding are discussed.
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PMID:Purification and cloning of the salivary peroxidase/catechol oxidase of the mosquito Anopheles albimanus. 1006 70

The catalytic activity of four lyophilized oxidative enzymes-horseradish peroxidase, soybean peroxidase, Caldariomyces fumago chloroperoxidase, and mushroom polyphenol oxidase-is much lower when directly suspended in organic solvents containing little water than when they are introduced into the same largely nonaqueous media by first dissolving them in water and then diluting with anhydrous solvents. The lower the water content of the medium, the greater this discrepancy becomes. The mechanism of this phenomenon was found to arise from reversible denaturation of the oxidases on lyophilization: because of its conformational rigidity, the denatured enzyme exhibits very limited activity when directly suspended in largely nonaqueous media but renatures and thus yields much higher activity if first redissolved in water. Two independent means were discovered for dramatically minimizing the lyophilization-induced inactivation, both involving the addition of certain types of excipients to the aqueous enzyme solution before lyophilization. The first group of excipients consists of phenolic and aniline substrates as well as other hydrophobic compounds; these presumably bind to the hydrophobic pocket of the enzyme active site, thereby preventing its collapse during dehydration. The second group consists of general lyoprotectants such as polyols and polyethylen glycol that apparently preserve the overall enzyme structure during dehydration. The activation effects of such excipients can reach into the tens and hundreds of fold. Moreover, the activations afforded by the two excipient groups are additive, resulting in up to a complete protection against lyophilization-induced inactivation when representatives of the two are present together.
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PMID:Striking activation of oxidative enzymes suspended in nonaqueous media. 1044 17

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry was used to study melanogenesis starting from Dopa and dopamine, the latter considered one of the precursors of neuromelanins. These substrates were left to react with the peroxidase - H(2)O(2) system, which is postulated to play an important role in melanin biosynthesis. Samples were prepared by ultrafiltering the substrate - enzyme solution after 30, 60, 120, 240 and 360 min of reaction and aliquots were immediately lyophilized. The reaction of dopamine with peroxidase - H(2)O(2) favoured the formation of dopamine oligomers up to octamers. In contrast, the action of either peroxidase or H(2)O(2) alone, studied for comparison, did not lead to melanin production and only dimeric and trimeric species were observed. Also for Dopa, analogous results were obtained in the presence of either peroxidase or H(2)O(2) alone, without melanin formation. Conversely, Dopa with the peroxidase - H(2)O(2) system led to the formation of a black precipitate after 120 min of reaction, and oligomers of 5,6-dihydroxyindole (DHI), an intermediate of melanogenesis, were detected, together with products of further oxidation. Faster kinetics were observed when Dopa was treated with tyrosinase, the enzyme catalysing the oligomerization of tyrosine to melanins, leading to the formation mainly of DHI oligomers.
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PMID:Application of matrix-assisted laser desorption/ionization mass spectrometry to the detection of melanins formed from Dopa and dopamine. 1049 88

An enhanced resistance to thermal denaturation was investigated for enzymes immobilized within hydrophobic semi-solid matrices compared with both free enzymes and polymer-entrapped enzymes. The bioelectrodes based on the immobilization of glucose oxidase, lactate oxidase, alcohol oxidase, polyphenol oxidase, peroxidase and L-amino acid oxidase within a carbon-paste matrix were constructed to examine their thermal stabilitiy at 60 degrees C or 80 degrees C. The rhodium/glucose oxidase-containing carbon-paste electrode was found to offer a remarkable stability when incubated at 60 degrees C over a long period of 4 months, with only a decrease of approx. 15% in activity. The comparative studies suggest that thermal stabilization established by this enzyme-immobilization procedure varies with the enzyme's inherent stability, the incubation temperature and the immobilizing reagent, such as pasting liquid.
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PMID:Remarkable thermostability of bioelectrodes based on enzymes immobilized within hydrophobic semi-solid matrices. 1051 99

Thermal and pressure inactivation of myrosinase from broccoli was kinetically investigated. Thermal inactivation proceeded in the temperature range 30-60 degrees C. These results indicate that myrosinase is rather thermolabile, as compared to other food quality related enzymes such as polyphenol oxidase, lipoxygenase, pectinmethylesterase, and peroxidase. In addition, a consecutive step model was shown to be efficient in modeling the inactivation curves. Two possible inactivation mechanisms corresponding to the consecutive step model were postulated. Pressure inactivation at 20 degrees C occurred at pressures between 200 and 450 MPa. In addition to its thermal sensitivity, the enzyme likewise is rather pressure sensitive as compared to the above-mentioned food quality related enzymes. By analogy with thermal inactivation, a consecutive step model could adequately describe pressure inactivation curves. At 35 degrees C, pressure inactivation was studied in the range between 0. 1 and 450 MPa. Application of low pressure (<350 MPa) resulted in retardation of thermal inactivation, indicating an antagonistic or protective effect of low pressure.
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PMID:Kinetic study of the irreversible thermal and pressure inactivation of myrosinase from broccoli (Brassica oleracea L. Cv. italica). 1055 54

It has been reported earlier that when macerated tea leaf is fermented at lower pH, the resultant black tea contains increased levels of theaflavin, an important quality marker in black tea. In an attempt to investigate the biochemistry and chemistry underlying this observation, in vitro oxidation experiments using polyphenol oxidase (PPO) from fresh tea leaves, horseradish peroxidase (POD), and tea catechins, precursors for theaflavins, were carried out. In vitro oxidation experiments using crude tea PPO resulted in higher content of theaflavins at pH 4.5 in comparison with pH 5.5, the normal pH of the macerated tea leaf. When purified PPO was used in the in vitro system, surprisingly a reversal of this trend was observed, with more theaflavins being formed at the higher pH. A combination of pure tea PPO and POD led to an observation similar to that with the crude enzyme preparation, suggesting a possible role for POD in the formation or degradation of theaflavin. POD was observed to oxidize theaflavins in the presence of H(2)O(2), leading to the formation of thearubigin, another black tea pigment. This paper demonstrates that tea PPO, while oxidizing catechins, generates H(2)O(2). The amount of H(2)O(2) produced is greater at pH 5.5, the optimum pH for PPO activity, than at pH 4.5. Hence, an observed increase of theaflavins in black teas fermented at pH 4.5 appears to be due to lower turnover of formed theaflavins into thearubigins.
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PMID:Role of polyphenol oxidase and peroxidase in the generation of black tea theaflavins. 1055 28

A study was made of the effect of high hydrostatic pressure treatment (50-500 MPa) combined with heat treatment (20-60 degrees C) on peroxidase (POD), polyphenol oxidase (PPO), and pectin methylesterase (PME) activities of tomato puree. Assays were carried out on fresh made tomato puree, and a 15 min treatment time was selected. Pressurization/depressurization treatments caused a continuous denaturation of soluble proteins at room temperature (20 degrees C). Also, ultrahigh hydrostatic pressure (UHP)/mild heat treatments produced a significant reduction (32.5%) of PME activity when a combination of 150 MPa/30 degrees C treatment was employed, while some activation was observed for treatments carried out at 335-500 MPa and different temperatures. A reduction of POD activity (25%) was obtained in tomato purees treated at 350 MPa/20 degrees C, but a combination of higher pressures and mild temperatures (30-60 degrees C) produced an enhancement of this activity. PPO activity did not show any significant change due to UHP/mild-temperature treatments in tomato product. Only a combination of 200 MPa/20 degrees C seemed to produce a significant loss (10%) in PPO activity.
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PMID:High-Pressure and Temperature Effects on Enzyme Inactivation in Tomato Puree. 1055 30

The reaction of opioid peptides with mushroom tyrosinase in the presence of an excess of a thiol compound gives rise to cysteinyldopaenkephalins (CDEnks). The major product is represented by the 5-S-CDEnk (80%) and the minor one by the isomer 2-S-CDEnk (20%). The adducts between leucine-enkephalin (Leu-enk) and cysteine have been isolated by high performance liquid chromatography (HPLC) and identified by amino acid analysis and electrospray ion mass spectrometry. 5-S-CDEnk is able to bind to opioid receptors in bovine brain membranes. Its binding affinity is higher for delta than for mu receptors and about 8-fold lesser than that exploited by Leu-enk. In the presence of the peroxidase/H(2)O(2) system, CDEnks can be converted into the corresponding pheo-opiomelanins.
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PMID:Cysteinyldopaenkephalins: synthesis, characterization and binding to bovine brain opioid receptors. 1071 71


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