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)

We have analyzed the tyrosinase coding region of three individuals having Type IA OCA within an extended family using genomic DNA amplification and dideoxy sequencing. Two of the affected individuals are dizygotic twins. All three have a common missense mutation at codon 81 (Pro----Leu) within exon I. The twins have a second missense mutation at codon 371 (Asn----Thr) within exon III and the third individual has a second missense mutation at codon 47 (Gly----Asp) within exon I. For each of these three individuals, the loss of enzyme function is the result of two different mutations, showing that they are compound heterozygotes of two mutant tyrosinase alleles.
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PMID:Molecular analysis of an extended family with type IA (tyrosinase-negative) oculocutaneous albinism. 167 41

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

Two analogues of alpha-MSH (Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2), Ac-[Nle4, Asp5, D-Phe7, Lys10]alpha-MSH4-10NH2 and Ac-[Nle4, Asp5, D-Phe7, Lys10] alpha-MSH4-10-NH2, were synthesized, and the melanotropic activities of the peptides were compared in several bioassays. Potencies were determined in the in vitro frog and lizard skin bioassays and in the S91 melanoma cell tyrosinase assay. Both analogues were equipotent or more potent than alpha-MSH in all bioassays, and the activities of the analogues were prolonged compared to alpha-MSH. The two analogues were very resistant to inactivation by purified proteolytic enzymes (alpha-chymotrypsin, trypsin, and pepsin). The two peptides could be topically applied and transdermally delivered across the skin of mice in vivo, resulting in a shift from pheomelanogenesis to eumelanogenesis within follicular melanocytes. The cyclic analogue exhibited greater potency, prolonged activity, and stability against enzyme inactivation than did the linear peptide. The significance of the findings for the further design of melanotropin analogues is discussed, as in the possible relevance of these melanotropin analogues for use in biomedical studies.
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PMID:Linear and cyclic alpha-melanotropin [4-10]-fragment analogues that exhibit superpotency and residual activity. 255 3

Trematode parasites protect their eggs with a tough tanned eggshell. Eggshell precursor proteins are synthesized and stockpiled within the extensive vitellaria of the animal. A major eggshell precursor protein with an apparent molecular weight of 31,000 and pI of 7.4 was isolated from the vitellaria of Fasciola hepatica. This protein, which represents 6-7% of the total protein in mature Fasciola, is unique in containing rather high levels of the amino acid 3,4-dihydroxyphenylalanine (DOPA), i.e., 110 residues per 1000. Other prominent amino acids are glycine, aspartic acid, and lysine. A prominent DOPA-containing tryptic peptide derived from eggshell precursor protein has the sequence Gly-Gly-Gly-DOPA-Gly-Gly-DOPA-Gly-Lys. DOPA residues disappear during the maturation of the eggshell and by treatment in vitro with mushroom polyphenol oxidase. This disappearance may be related to the formation of cross-links in the eggshell protein.
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PMID:Presclerotized eggshell protein from the liver fluke Fasciola hepatica. 342 7

Opioid peptides can be converted by tyrosinase into melanin-like compounds, in which the peptide moiety is retained. Such pigments, named opio-melanins, exhibit a characteristic absorption spectrum with a maximum at about 330 nm and a different solubility behaviour with respect to dopa-melanin, being completely soluble in hydrophylic solvents at neutral and basic pH. Opio-melanins precipitate in aqueous solutions below pH 5.0, and show apparent pKa values of 3.1, 3.6 and 4.4 for Tyr-Gly-melanin, Tyr-Gly-Gly-melanin and leuenk-melanin, respectively. The concomitant oxidation of dopa and opioid peptides by tyrosinase produces mixed polymers, showing the distinctive absorption peak at 330 nm. In the dark, in the pH range 5.5-7.0 the pigments are completely stable, whereas H2O2 addition provokes a slight degradation. At higher pH values or under simulated solar illumination with or without hydrogen peroxide, bleaching occurs more rapidly than in dopa-melanin. Upon photoirradiation the absorption spectrum of opio-melanins undergoes a marked variation, the peak at 330 nm being replaced by a broad shoulder in the range 280-350 nm. The absorption spectra of native and bleached pigments and the extent of opio-melanins degradation by bleaching agents, confirm the hypothesis that the different initial structure of the precursors accounts for a final diverse polymeric architecture of these pigments with respect to dopa-melanin.
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PMID:Spectroscopic features of native and bleached opio-melanins. 782 10

N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymers containing doxorubicin (DOX, approximately 8% by weight) bound via the lysosomally degradable spacer Gly-Phe-Leu-Gly and, in certain cases, also melanocyte-stimulating hormone (MSH, 5-10% by weight) were synthesized with the aim of developing a drug conjugate for site-specific delivery to malignant melanoma. Polymer-bound MSH, like free MSH, was able to stimulate tyrosinase activity in B16F10 cells in vitro, confirming the ability of conjugated hormone to interact with the MSH receptor. Similarly, a 125I-labelled conjugate containing MSH was captured by B16F10 cells in vitro more rapidly than a similar polymer without the targeting moiety. HPMA copolymers containing DOX bound via the lysosomally degradable Gly-Phe-Leu-Gly linkage were cytotoxic to a mouse melanoma cell line (M3 S91) in vitro, the MSH-containing conjugate being more active than that without (although the difference in the ID50 was not significant). When administered intraperitoneally or intravenously to C57BL/6J mice bearing intraperitoneal B16F10 tumours, HPMA copolymers containing DOX linked via this biodegradable spacer (with or without MSH) significantly increased animal survival, the maximum ratio of the mean survival of the test group (T) to that of the untreated control (C) T/C observed (approximately 200) over the dose range 5-20 mg DOX/kg being similar to that seen for free DOX. In contrast, neither polymer conjugates containing DOX bound via a non-degradable linkage (Gly-Gly) nor free MSH showed antitumour activity. In mice bearing established subcutaneous B16F10 tumours, biodegradable polymer-bound DOX conjugates given intraperitoneally were more effective than free DOX (which was virtually inactive in this system); conjugates containing MSH were significantly more effective than those without, the maximum T/C being approximately 148 and 324 respectively. Preliminary pharmacokinetic experiments showed evidence of selective MSH targeting of polymer conjugates to subcutaneous B16F10.
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PMID:Polymeric drug-carriers containing doxorubicin and melanocyte-stimulating hormone: in vitro and in vivo evaluation against murine melanoma. 806 63

In vitro experiments are reported showing that NAD(P)H:(quinone acceptor) oxidoreductase (QR), purified from Glycine max seedlings, reduces Leu- and Met-enkephalin-tyrosinase oxidation products, in the presence of NADH or NADPH. QR was not capable to catalyze the reduction of N-acetyl-dopaquinone formed by the cation of mushroom tyrosinase on N-acetyl-L-tyrosine, while it was able to reduce dopachrome. The results support the hypothesis that QR can inhibit the formation of melanin-like compounds, as catalyzed by the action of tyrosinase on Leu-enkephalin and Met-enkephalin. It is proposed that, in the presence of NAD(P)H as the electron donor, the inhibition occurs by the specific conversion of the dopachrome-derivative into the reduced precursor, leucodopachrome-derivative.
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PMID:Effect of NAD(P)H:quinone oxidoreductase on tyrosinase-mediated oxidation of opioid neuropeptides Leu-enkephalin and Met-enkephalin. 867 15

We have previously reported that melatonin was an effective lightening agonist in the teleost Synbranchus marmoratus, the amphibians Rana pipiens and Bufo ictericus, and in the lizard Anolis carolinensis. The hormone, previously applied to the preparations, effectively inhibited alpha-MSH darkening activity in a dose-independent manner, and was also able to reverse MSH-induced darkening. We presently describe the inhibitory effect of the indoleamine on the murine melanoma cell proliferation. Interestingly, the hormone also stimulated tyrosinase activity, with a correlated increase in melanin content. We also demonstrate that in a diverse lizard species, Urosaurus ornatus, the indoleamine was totally ineffective. The competitive MSH antagonistic activity of H-His-D-Arg-Ala-Trp-D-Phe-Lys-NH2 has been demonstrated previously in R. pipiens and U. ornatus. Herein, its inhibitory activity is also reported in another lizard species, A. carolinensis. However, this MSH analogue was inactive in S. marmoratus, and in murine melanoma cells. On the other hand, the 7 thru 10 alpha-MSH fragment, Ac-Phe-Arg-Trp-Gly-NH2, although ineffective in S. marmoratus and R. pipiens, was an alpha-MSH antagonist in A. carolinensis. Surprisingly, in the melanoma cell line, the MSH fragment exhibited no agonist or antagonist activity, but dramatically potentiated the MSH-induced increase in tyrosinase activity. These data might suggest that the fragment is participating either in the process of facilitation or in positive cooperativity. The present results, taken together with our previously reported data, demonstrate a major interspecies diversity of the MC1 subtype of melanocortin receptor, and point out the relevance of the membrane microenvironment for the final receptor configuration.
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PMID:Comparative biological activities of alpha-MSH antagonists in vertebrate pigment cells. 907 3

Opioid peptides and other Tyr-NH2-terminal peptides are substrates in vitro for mushroom and sepia tyrosine, giving rise to synthetic melanins retaining the peptide moiety (opiomelanins). The melanopeptides are characterized by a total solubility in hydrophylic solvents at neutral and basic pH. Opioid peptides (enkephalins, endorphins, and esorphins), if oxidized by tyrosinase in the presence of Dopa, are easily incorporated into Dopa-melanin, producing mixed-type pigments that can also be solubilized in hydrophylic solvents. Melanins derived from opioid peptides exhibit paramagnetism, as evidenced by an EPR spectrum identical to that of Dopa-melanin. However, the presence of the linked peptide chain is able to influence dramatically the electron transfer properties and the oxidizing behaviour of the melanopeptides, so that whereas Tyr-Gly-melanin appears to behave as Dopa-melanin, Enk-melanin does not exhibit any oxidizing activity. Opiomelanins are characterized by a peculiar UV-VIS spectrum; that is, by the presence of a distinct peak (330 nm) that disappears upon chemical treatment by acid hydrolysis. Opiomelanins are stable pigments at neutral and basic pH in the dark, whereas the addition of H2O2 leads to a 15% degradation. Under stimulated solar illumination, opiomelanins are more easily destroyed with respect to Dopa-melanin, with increasing degradation when exposed to increased hydrogen peroxide concentrations and more alkaline pH. Some speculations on the possible existence and role of opiomelanins have been outlined.
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PMID:Melanins from opioid peptides. 912 50

Opioid peptides and other Tyr-NH2-terminal peptides are substrates in vitro for mushroom and sepia tyrosinase giving rise to synthetic melanins retaining the peptide moiety (opiomelanins). The melanopeptides are characterized by a total solubility in hydrophilic solvents at neutral and basic pH. Opioid peptides (enkephalins, endorphins, esorphins), if oxidized by tyrosinase in the presence of Dopa are easily incorporated into Dopa-melanin, producing mixed-type pigments which can also be solubilized in hydrophilic solvents. Melanins deriving from opioid peptides exhibit paramagnetism as evidenced by an EPR spectrum identical to that of Dopa-melanin. However the presence of the linked peptide chain is able to influence dramatically the electron transfer properties and the oxidizing behaviour of the melanopeptides, so that whereas Tyr-Gly-melanin appears to behave as Dopa-melanin, Enk-melanin does not exhibit any oxidizing activity. Opiomelanins are characterized by a peculiar UV-VIS spectrum i.e. by the presence of a well distinct peak (330 nm) disappearing upon chemical treatment by acid hydrolysis. Opiomelanins are stable pigments at neutral and basic pH in the dark, whereas H2O2 addition leads to a 15% degradation. Under simulated solar illumination opiomelanins are more easily destroyed with respect to Dopa-melanin with increasing degradation of exposed to increased hydrogen peroxide concentrations and more alkaline pH. Some speculations on the possible existence and role of opiomelanins have been outlined.
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PMID:[New possible pathways for melanogenesis: opiomelanins]. 917 71


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