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)

With the objective of elucidating the mechanisms of dioxygen activation by transition metal complexes, we have investigated functional models of some metalloenzymes, such as phenoxazinone synthase and catechol oxidase, based on bisdimethylglyoximatocobalt(II) and -iron(II) complexes. Kinetic studies and the identification of intermediates permitted to establish a free radical mechanism. The catalytic cycle involves H-atom abstraction from the catechol by a superoxo complex, generating a semi-quinone anion radical, which coordinates to the metal, affording new complexes. Useful free-radical intermediates in biological systems are not impossible since tyrosinase has been shown to contain coordinated tyrosyl radical as an integral part of the active enzyme. We have interpreted the structure-reactivity relationship observed in the reaction of the [Pd2Cl2(dppm)2] dimer with arenesulfonyl azides.
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PMID:[Kinetics and mechanisms of the reactions of transition metal complexes]. 1137 32

The concentration of melanin determines the intensity of colors of the skin and hair of animals. Melanin pigments are tyrosine-based polymers formed in melanocytes within specialized organelles called melanosomes. In order to understand the mechanism of melanin polymerization, lactoferrin, a basic protein with a pI value of 9.0, has been used to produce melanin. Lactoferrin is a monomeric iron-binding protein with a molecular weight of 80 kDa. The crystals of lactoferrin were soaked in a solution containing dihydroxyphenylalanine (DOPA) and tyrosinase enzyme. These crystals were used for X-ray intensity data collection. The intensity data were collected to 2.7-A resolution to an overall completeness of 91% with an R(sym) of 0.071. The crystals belong to orthorhombic space group P2(1)2(1)2(1) with cell dimensions: a = 85.0 A, b = 99.8 A, c = 103.4 A. The structure was determined by molecular replacement method, using the model of diferric mare lactoferrin, and refined to an R-factor 0.215 (R(free) = 0.287) for all the data to 2.7-A resolution. The final model comprises 5,281 protein atoms from 689 amino acids, 2Fe(3+), 2CO(2-)(3) ions, 2 indole-5,6-quinone molecules (IQ), and 73 water molecules. Two IQ molecules, one in each lobe, bind to lactoferrin. In the C-lobe, the IQ binds in the iron-binding cleft, whereas in the N-lobe, it is located in the side pocket between two alpha-helices, filled with solvent molecules in the native iron-saturated mare lactoferrin. The IQ molecules interact with protein molecule mainly through glutamic acid in both lobes, without significant perturbation to the protein structure. The orientation of N- and C-lobes in the present structure is similar to that observed in the native iron-saturated protein. However, as a result of the binding of IQ molecules, the orientations of the domains N1, N2 and C1, C2 in the two cases differ slightly.
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PMID:Lactoferrin-melanin interaction and its possible implications in melanin polymerization: crystal structure of the complex formed between mare lactoferrin and melanin monomers at 2.7-A resolution. 1159 26

Three adhesive polyoctapeptides (X/Y-Gly-Tyr-Ser-Ala-Gly-Tyr-Lys)n (X, Thr and Ala: Y, Thr:Ala = 3:2), which are the C-terminal octapeptide sequences shared by all those consensus motifs of a ribbed mussel Geukensia demissa adhesive protein (RMAP), have been synthesized by the polycondensation of the active esters. The correlation between wettability and adhesion with the alternative substitution by hydrophobic Ala and hydrophilic Thr in the synthetic RMAPs in aqueous solution and as films on high and low surface free energy (sfe) surfaces has been investigated by surface chemical approaches. The side chain moieties of RMAPs arrange their local conformation to adapt to the inherent surface character, and they orientate on high and low sfe surfaces. On a high sfe glass the hydrophilic side chains of the RMAP molecules face toward the surface, and on a low sfe polyethylene (HDPE) the hydrophobic side chains face toward the surface. The bonding strengths of synthetic RMAPs on glass and HDPE with and without enzymatic oxidation have been examined. Increased starting concentration exhibited the strongest adhesive capability (7.5 kgf/cm2) on alumina due to the increased cohesion among RMAP molecules. As another factor to increase adhesive ability, the intermolecular cross-linking among RMAP molecules by tyrosinase increases their adhesive capability by about 20% on HDPE, glass, and alumina except iron.
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PMID:Synthesis and wettability characteristics of model adhesive protein sequences inspired by a marine mussel. 1171 Jan 79

After reduction of phytate with phytase, water slurries of two high-tannin cereal flours were incubated with polyphenol oxidase (mushroom tyrosinase), and the effects on different phenolic groups and on in vitro accessible iron were studied. Enzyme incubation was also performed after cooking, soaking, and germination of the cereals. Phytase incubation significantly decreased the phytate content, and incubation with polyphenol oxidase had a reducing effect on the total phenol content, as well as on the amount of catechol and resorcinol groups. The in vitro accessible iron increased when the cereals were incubated with phytase and polyphenol oxidase, and the highest accessibility of iron was obtained when the germinated samples were incubated. The results from this study imply that oxidation of polyphenols in high-tannin cereals, after reduction of phytate, may be used to increase the bioavailability of iron in foods prepared from these cereals.
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PMID:Oxidation of polyphenols in phytate-reduced high-tannin cereals: effect on different phenolic groups and on in vitro accessible iron. 1171 70

In the presence of iron or copper ions, the course of the oxidation in air of 5-S-cysteinyldopa (1), the main biosynthetic precursor of pheomelanins and trichochromes, was markedly changed affording two main products. One of these was identified as the oxobenzothiazine 8, previously obtained under nonphysiologically relevant conditions, while the other was characterized as the novel hydroxybenzothiazole 9. Besides 8 and 9, carboxylated and noncarboxylated benzothiazine products were obtained by persulfate oxidation of 1 in the presence of iron or copper ions. The ratio of formation yields of carboxylated/noncarboxylated benzothiazines, determined after reduction of the mixture, was lower than that of the control reaction run in the absence of metal ions, and much lower than that of the oxidation carried out in the presence of zinc ions, in agreement with a recent report. Notably, 8 and 9 were formed in variable yields under different oxidation conditions including tyrosinase/O(2), peroxidase/hydrogen peroxide, and the hydrogen peroxide/or (9E,11Z,13S)-13-hydroperoxyoctadeca-9,11-dienoic acid/Fe(III) systems. Mechanistic routes to 8 and 9 were proposed based on the results of experiments involving in situ generation of labile benzothiazine intermediates. Overall, these results allow to formulate an improved biosynthetic scheme in which metal ions act as critical regulatory factors determining pheomelanin vs. trichochromes formation.
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PMID:Metal ions as potential regulatory factors in the biosynthesis of red hair pigments: a new benzothiazole intermediate in the iron or copper assisted oxidation of 5-S-cysteinyldopa. 1204 96

Amphibia Kupffer cells (i.e., liver resident macrophages) show many common characteristics when compared with Mammalia Kupffer cells: filopodia, microvillous-like structures, lamellipodia, fuzzy coat, coated vesicles, bristled vacuoles, nonspecific esterase activity, and pinocytotic and phagocytic activity are present both in Amphibia and Mammalia Kupffer cells. On the other hand, some differences are present between Kupffer cells of both zoological classes: phagocytosed red cells and their derivatives, iron-protein complexes, and lipofuscin bodies are normally present in Amphibia Kupffer cells, but absent in the same cells of healthy mammals. Worm-like structures are not seen in Amphibia and endogenous peroxidase activity is very weak in these animals compared with Mammalia. The most important difference lies in the ability of Amphibia Kupffer cells to produce melanins: in fact the tyrosinase gene is expressed, "melanosome centers" are present, and dopa oxidase activity is demonstrable.
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PMID:Amphibia Kupffer cells. 1211 30

Copper is next to iron the most important element in the biological transport, storage and in redox reactions of dioxygen. A bioanalogous activation of dioxygen with copper complexes is used for catalytical epoxidation, allylic hydroxylation and oxidative coupling of aromatic substrates, for example. With stereochemical information in form of chiral ligands, enantioselective reactions may be possible. Another aspect of interest on copper catalyzed reactions with dioxygen is that the exact mechanism and biological function of some enzymes (especially catechol oxidase) is yet not fully clear. For studies mimicking the copper-containing catechol oxidase appropriate chiral steroid ligands with defined stereochemistry and conformation have been synthesized. The four diastereomeric 16,17-aminoalcohols of the 3-methoxy-estra-1,3,5(10)-triene series have been condensed with salicylic aldehyde and different beta-ketoenols to the chiral ligand types 1-5. These compounds with different steric and electronic properties and different arrangements of the neighboring hydroxy and nitrogen functions were reacted with copper(II) acetate to copper complexes. The structure of these complexes will be discussed. The bioanalogous oxidation of 3,5-di-tbutyl-catechol (dtbc) to the corresponding quinone was catalyzed by most of the complexes, indicating their ability to activate dioxygen. The trans configurations c and d showed an activity one magnitude higher than the cis configurations a and b. Comparing compounds with the same diastereomeric configuration, the main influence was that of the peripheral R(1-3) substituents at the beta-ketoenaminic group which are useful for the fine-tuning of the properties of the copper atoms like redox potential and Lewis acidity.
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PMID:Synthesis, structure and catechol-oxidase activity of copper(II) complexes of 17-hydroxy-16-(N-3-oxo-prop-1-enyl)amino steroids. 1223 Nov 19

Historically, in vivo imaging methods have largely relied on imaging gross anatomy. More recently it has become possible to depict biological processes at the cellular and molecular level. These new research methods use magnetic resonance imaging (MRI), positron emission tomography (PET), near-infrared optical imaging, scintigraphy, and autoradiography in vivo and in vitro. Of primary interest is the development of methods using MRI and PET with which the progress of gene therapy in glioblastoma (herpes simplex virus-thymidine kinase) and Parkinson's disease can be monitored and graphically displayed. The distribution of serotonin receptors in the human brain and the duration of serotonin-receptor antagonist binding can be assessed by PET. With PET, it is possible to localize neurofibrillary tangles (NFTs) and beta-amyloid senile plaques (APs) in the brains of living Alzheimer disease (AD) patients. MR tracking of transplanted oligodendrocyte progenitors is feasible for determining the extent of remyelinization in myelin-deficient rats. Stroke therapy in adult rats with subventricular zone cells can be monitored by MRI. Transgene expression (beta-galactosidase, tyrosinase, engineered transferrin receptor) can also be visualized using MRI. Macrophages can be marked with certain iron-containing contrast agents which, through accumulation at the margins of glioblastomas, ameliorate the visual demarcation in MRI. The use of near-infrared optical imaging techniques to visualize matrix-metalloproteinases and cathepsin B can improve the assessment of tumor aggressiveness and angiogenesis-inhibitory therapy. Apoptosis could be detected using near-infrared optical imaging representation of caspase 3 activity and annexin B. This review demonstrates the need for neurohistological research if further progress is to be made in the emerging but burgeoning field of molecular imaging.
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PMID:Molecular imaging: Bridging the gap between neuroradiology and neurohistology. 1502 22

The crystal structure and catecholase-like activity of a mononuclear complex, Cu(EDTB)(NO3)2.C2H5OH (here EDTB stands N,N,N',N'-tetrakis(2'-benzimidazolyl methyl)-1,2-ethanediamine) has been studied in comparison with a binuclear complex Cu2(EDTB)(NO3)4.3H2O. The results show that the reactive rate constants increase with increases of reaction temperature and pH value of intermediate. Electrospray ionization mass spectrum (ESI-MS) shows that tautomerism isomers of catechol with the title complex exist in reaction solution, and catechol is oxidized to quinone, then it is further oxidized resulting in muconic acid and its derivatives via an intradiol mechanism, just like that catalyzed by a mononuclear non-heme iron-containing dioxygenase.
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PMID:Crystal structure and catecholase-like activity of a mononuclear complex [Cu(EDTB)]2+ (EDTB=N,N,N',N'-tetrakis(2'-benzimidazolyl methyl)-1,2-ethanediamine). 1527 7

Dioximato-cobalt(II), -iron(II) and -manganese(II) complexes (1)-(6), acting as functional catecholase and phenoxazinone synthase models, exhibit a deuterium kinetic isotope effect predicted by theory (k4H/k4D < or = 3) in the catalytic oxidative dehydrogenation of 3,5-di-tert-butylcatechol and 2-aminophenol by O2. KIEs in the range of (k4H/k4D approximately 1.79-3.51) are observed with (1) and (2) as catalysts, pointing to hydrogen atom transfer in the rate-determining step from the substrate hydroxy group to the metal-bound superoxo ligand. Less significant KIEs (1.06-1.20) are exhibited by catalysts systems (3)-(6), indicating that proton-coupled electron transfer is the preferred route in those cases.
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PMID:Hydrogen atom vs electron transfer in catecholase-mimetic oxidations by superoxometal complexes. Deuterium kinetic isotope effects. 1561 28


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