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 reaction products of peroxidase, a hydrogen donor and hydrogen peroxide decreased the amount of lysine recovered from proteins after acid hydrolysis. Oxidation of peroxidase treated proteins with performic acid prior to hydrolysis formed alpha-amino adipic acid indicating that the peroxidase or the quinones formed by peroxidase had oxidatively deaminated some lysyl residues of the protein to form lysyl aldehyde. Gel filtration and polyacrylamide gel electrophoresis revealed dimers, trimers and higher protein polymers that were not detected when peroxidase was omitted. Since some of the protein polymers were not dissociated by gel electrophoresis in the presence of dodecyl sulfate, urea and mercaptoethanol, it suggests that the free radicals or quinones formed by peroxidase had interacted with or cross-linked protein molecules by the formation of covalent bonds. Oxidative enzymes like peroxidase and polyphenol oxidase may lower the nutritive value of proteins by the oxidative deamination of lysine, reaction with cysteine and methionine and by cross-linking protein molecules to reduce their susceptibility to enzymatic hydrolysis.
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PMID:Cross-linking of protein by peroxidase. 2 Jul 49

When Rana cancrivora were collected from fresh water and dehydrated (weight loss 4-10%) by exposure to saline, the plasma titre of hydro-osmotic activity, measured by amphibian bladder assay, was increased three-to fourfold. This activity, which was abolished by thioglycollate and by incubation with tyrosinase or trypsin, was ascribed to vasotocin. The plasma vasotocin activities (hydrated and dehydrated frogs respectively) were estimated to be 0-03-0-5 and 0-15-0-25 mug/1; if referred to oxytocin as a standard the equivalent values were 10 and 30-60 mu./ml. Assuming that the increase represented released pituitary hormone, the amount of vasotocin released by osmotic dehydration was calculated to be of the order of 1 ng. Pituitary glands of hydrated and dehydrated frogs were estimated to have 0.15 and 0-18 mug vasotocin/gland respectively. The possible physiological function of released vasotocin in promoting reabsorption of urea from the urinary bladder is discussed in relation to the euryhaline ability of R. cancrivora.
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PMID:Vasotocin-like activity in the plasms of the euryhaline frog (Rana cancrivora) after transfer from fresh water to saline. 81 47

The purification of two isoenzymes of tyrosinase has been carried out in Harding-Passey mouse melanoma. One is found in the cytosol and the other one bound to melanosomes. Both migrate as single bands on sodium dodecyl sulphate/polyacrylamide gels, having an apparent Mr of 58 000. Solubilized particulate tyrosinase showed an aggregation equilibrium involving a monomer, tetramer, octamer and a high-Mr micellar form with Brij 35, the solubilizing agent. H.p.l.c. studies indicated a interconversion between those species, the monomer contribution increasing with the sample dilution. The tetramer and the octamer probably represent the predominant forms in vivo. Soluble tyrosinase showed a simpler aggregation equilibrium, involving two forms, monomer and tetramer, with the same interconversion pattern. Fluorescence studies suggested that tryptophan residues were exposed to the aqueous environment when tyrosinase was dissociated by dilution. Tyrosinase shows a tendency to aggregate, at low protein concentration, and a resistance to dissociation by urea or SDS so remarkable that gel-permeation chromatography in 4M-urea does not affect the equilibrium, and the band obtained on SDS/polyacrylamide-gel electrophoresis is a dimer.
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PMID:Aggregation equilibria of tyrosinase of Harding-Passey mouse melanoma. 392 35

Oxidation of tyrosine in the presence of bovine lens proteins leads to the formation of brown or black melanoproteins. Both tyrosinase and the oxidizing system of ferrous sulphate-ascorbic acid-EDTA are effective. The fluorescence of the lens proteins is both altered and enhanced by the tyrosine-oxidizing systems. Their fluorescence spectra resemble those of urea-insoluble proteins of human cataractous lens and of 1,2-naphthaquinone-proteins of naphthalene cataract. The lens proteins lose their thiol groups and, in acid hydrolysates of treated beta-and gamma-crystallins, a substance has been detected chromatographically that behaves similarly to a compound formed when 3,4-dihydroxyphenylalanine (dopa) is oxidized by tyrosinase in the presence of cysteine. Analysis and behaviour of this substance from hydrolysates of lens proteins suggest that it is a compound of cysteine and dopa.
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PMID:Reaction of tyrosine oxidation products with proteins of the lens. 497 Dec 87

1. Purified pro-tyrosinase from epidermis of the frog Rana esculenta ridibunda can be activated in vitro by several proteinases (trypsin, alpha-chymotrypsin, Pronase) and by light. 2. Both pro-tyrosinase and tyrosinase are composed of a single type of subunit having pI 7.2 and approximate molecular weights 68000 and 62000 respectively. A peptide of low molecular weight is released as a consequence of the proteolytic activation. Pro-tyrosinase and tyrosinase have different quaternary structures, the proenzyme being a dimer of Mr approx. 115000 and the enzyme a tetramer of Mr approx. 210 000. 3. The activation process was affected by several agents (L-3,4-dihydroxyphenylalanine, urea, formamide) that prevented, partially or totally, the activation of pro-tyrosinase. 4. The activation of pro-tyrosinase seems to be the result of a cleavage of the polypeptide chain that determines changes in tertiary or quaternary structure.
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PMID:The process for the activation of frog epidermis pro-tyrosinase. 681 26

Histamine displayed specific and saturable binding to membrane fractions of the human melanoma cell line MM96E (Kd = 72.4 nM and Bmax = 487 fmol/mg protein). There was weak competition with isothioureas that inhibit tyrosinase in intact cells: dimaprit (an H2 agonist) nordimaprit and S-[2-(N,N-diisopropyl)ethyl]isothiourea (DINOR). Under culture conditions, rapid, pH-dependent hydrolysis of the isothioureas occurred, with cleavage to urea and a thiol which spontaneously oxidised to the disulphide. The H3 agonist imetit, which also inhibited tyrosinase, behaved similarly. The disulphide breakdown product of DINOR but not the thiol inhibited tyrosinase activity in intact MM96E cells to a similar extent as DINOR itself. Isothioureas with more bulky substituents, however, were stable in culture and did not inhibit tyrosinase. The results show that (a) certain histaminergic drugs exert effects via a disulphide hydrolysis product independently of the histamine H2 receptor, and (b) beta-aminoethyldisulphides are depigmenting agents.
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PMID:Dimaprit analogues inhibit tyrosinase via a disulphide breakdown product independently of the histamine H2 receptor. 800 3

The in vitro enzymatic polymerization of the polyphenolic protein purified from the mussels Aulacomya ater, Mytilus edulis chilensis and Choromytilus chorus was studied. Mushroom tyrosinase was used to oxidize the dopa residues present in these proteins, and polymerization was monitored by acid-urea polyacrylamide gel electrophoresis. The protein from A. ater polymerized at a faster rate than the other two. Amino acid analysis of the crosslinked protein showed a notable decrease in the content of dopa, but no significant change of other amino acids. This suggests that crosslink formation may be limited to the oxidized dopa derivatives of the protein molecules.
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PMID:In vitro polymerization of mussel polyphenolic proteins catalyzed by mushroom tyrosinase. 1100 80

The frequent loss of both INK4a and ARF in melanoma raises the question of which INK4a-ARF gene product functions to suppress melanoma genesis in vivo. Moreover, the high incidence of INK4a-ARF inactivation in transformed melanocytes, along with the lack of p53 mutation, implies a cell type-specific role for INK4a-ARF that may not be complemented by other lesions of the RB and p53 pathways. A mouse model of cutaneous melanoma has been generated previously through the combined effects of INK4a(Delta2/3) deficiency (null for INK4a and ARF) and melanocyte-specific expression of activated RAS (tyrosinase-driven H-RAS(V12G), Tyr-RAS). In this study, we made use of this Tyr-RAS allele to determine whether activated RAS can cooperate with p53 loss in melanoma genesis, whether such melanomas are biologically comparable to those arising in INK4a(Delta2/3-/-) mice, and whether tumor-associated mutations emerge in the p16(INK4a)-RB pathway in such melanomas. Here, we report that p53 inactivation can cooperate with activated RAS to promote the development of cutaneous melanomas that are clinically indistinguishable from those arisen on the INK4a(Delta2/3) null background. Genomewide analysis of RAS-induced p53 mutant melanomas by comparative genomic hybridization and candidate gene surveys revealed alterations of key components governing RB-regulated G(1)/S transition, including c-Myc, cyclin D1, cdc25a, and p21(CIP1). Consistent with the profile of c-Myc dysregulation, the reintroduction of p16(INK4a) profoundly reduced the growth of Tyr-RAS INK4a(Delta2/3-/-) tumor cells but had no effect on tumor cells derived from Tyr-RAS p53(-/-) melanomas. Together, these data validate a role for p53 inactivation in melanomagenesis and suggest that both the RB and p53 pathways function to suppress melanocyte transformation in vivo in the mouse.
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PMID:Dual inactivation of RB and p53 pathways in RAS-induced melanomas. 1123 48

The suitability of 4-di(2-chloroethyl)aminoanilino-4-hydroxyphenethylaminomethanone 2 to act as a prodrug for melanocyte-directed enzyme prodrug therapy (MDEPT) is assessed. Thus its synthesis, ability to generate a cytotoxic agent upon exposure to tyrosinase, and stability within different sera are reported. A comparison is made to illustrate that the new urea prodrug 2 is a more suitable candidate for MDEPT than the corresponding carbamate prodrug 1.
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PMID:Synthesis and analysis of urea and carbamate prodrugs as candidates for melanocyte-directed enzyme prodrug therapy (MDEPT). 1205 51

Using L-DOPA as a probe, phenoloxidase (PO) from Penaeus chinensis hemolymph was purified by gel-filtration and ion-exchange chromatography, and characterized in terms of its molecular weight and enzymatic properties in this study. It was found that prophenoloxidase (proPO) isolated as monomeric protein had a molecular weight of 87.5 kD, and a 77 kD phenoloxidase molecule was often contained in preparations. The 87.5 kD proPO had a very low enzymatic activity on 0.02 mmol/L L-DOPA, whereas the 77 kD PO had a very high enzymatic activity on L-DOPA. Enzymatic activity of PO against L-DOPA was optimal at pH 6.0, temperature of 40 degrees, and with an apparent K(m) value of 1.99 mmol/L. The PO activity was extremely sensitive to ascorbic acid, cysteine and dithiothreitol, very sensitive to thio urea, however not sensitive to sodium sulfite, citric acid and benzoic acid, confirmed that it was a phenoloxidase, combined with its specific oxidase activity on substrate of monophenol and L-DOPA, indicate that it was a tyrosinase type phenoloxidase. This enzyme is very sensitive to EDTA and metal ions, its activity is strongly enhanced by Mg(2+) and strongly inhibited by Cu(2+), which indicates that this PO is probably a kind of metalloenzyme.
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PMID:[Purification and partial biochemical characterization of phenoloxidase from Penaeus chinensis]. 1219 61


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