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 amino-acid sequence of tyrosinase from Neurospora crassa (monophenol,dihydroxyphenylalanine:oxygen oxidoreductase, EC 1.14.18.1) is reported. This copper-containing oxidase consists of a single polypeptide chain of 407 amino acids. The primary structure was determined by automated and manual sequence analysis on fragments produced by cleavage with cyanogen bromide and on peptides obtained by digestion with trypsin, pepsin, thermolysin, or chymotrypsin. The amino terminus of the protein is acetylated and the single cysteinyl residue 96 is covalently linked via a thioether bridge to histidyl residue 94. The formation and the possible role of this unusual structure in Neurospora tyrosinase is discussed. Dye-sensitized photooxidation of apotyrosinase and active-site-directed inactivation of the native enzyme indicate the possible involvement of histidyl residues 188, 192, 289, and 305 or 306 as ligands to the active-site copper as well as in the catalytic mechanism of this monooxygenase.
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PMID:Amino acid sequence of tyrosinase from Neurospora crassa. 15 Dec 79

The isozymes of tyrosinase from normal and malignant melanocytes were studied; the data indicates that each consists of a basic tyrosinase polypeptide, and differs by post-translational modifications. T3 represents the de novo form of the enzyme; it is converted to T1 in vivo by the addition of sialic acids and neutral sugars, and in turn, to T4 by complexing with mealanosomal membrane constituents. The T2 isomer is suggested to be an artefact of the electrophoretic procedure, and due to deamidation of T3. It is shown that the apparent kinetics of enzyme activity are unafffected by any of these modifications.
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PMID:Mammalian tyrosinase. Structural and functional interraltionship of isozymes. 41 82

Tyrosinase (EC 1.14.18.1) is a copper-containing metalloglycoprotein that catalyzes several steps in the melanin pigment biosynthetic pathway; the hydroxylation of tyrosine to L-3,4-dihydroxyphenylalanine (dopa) and the subsequent oxidation of dopa to dopaquinone. It has been proposed that tyrosinase is also able to oxidize 5,6-dihydroxyindole (DHI), a later product in the melanogenic pathway, to indole-5,6-quinone. Tyrosinase enzymatic activity is deficient in patients with classic type I oculocutaneous albinism (OCA), and more than 50 distinct mutations have now been identified in the tyrosinase genes of such patients. To determine the effects of the various tyrosinase gene mutations on the catalytic activities of the enzyme, we carried out site-directed mutagenesis of human tyrosinase cDNA, transiently expressed the mutant cDNAs in transfected HeLa cells, and assayed the resultant encoded proteins for tyrosine hydroxylase, dopa, and DHI oxidase activities, and resulting melanin production. The tyrosine hydroxylase activity of normal tyrosinase is thermostable, whereas its dopa oxidase and DHI oxidase activities are temperature-sensitive. Although all amino acid substitutions tested generally affected the dopa oxidase and DHI oxidase activities in parallel, several exerted distinctly different effects on the tyrosine hydroxylase activities. Together, these results confirm the DHI oxidase activity of mammalian tyrosinase and suggest that the dopa oxidase and DHI oxidase activities of tyrosinase share a common catalytic site, whereas the tyrosine hydroxylase catalytic site is at least partially distinct in the tyrosinase polypeptide.
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PMID:Mutational mapping of the catalytic activities of human tyrosinase. 142 11

Insolubilizing studies of water-soluble synthetic polypeptides containing lysine residues were examined using organic aliphatic and aromatic cross-linking agents such as dialdehydes, diacyl chlorides and diactive ester, together with an enzyme tyrosinase, in water and simulated seawater systems. The cross-linking reaction was characterized by the viscosity and turbidity changes. Among the organic cross-linking agents used aliphatic glutaraldehyde and aromatic o-phthalaldehyde were the most effective. When excess organic cross-linking agents were added to the lysine polypeptide systems, the corresponding solid gels were formed. As a whole, the molecular weight of the samples, the amino acid compositions, the cross-linking agent used, the molar ratios between cross-linking agents and functional residues and system pH were found to have roles in the insolubilizing reaction and the gel formation. The cross-linking results obtained were compared with those of the polypeptide-tyrosinase systems, whose deep brownish red colour was decolorized by the addition of L-ascorbic acid.
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PMID:Cross-linking and gel formation of water-soluble lysine polypeptides. An insolubilization model reaction for adhesive proteins. 151 2

Type I (tyrosinase-deficient) oculocutaneous albinism (OCA) results from mutations of the gene encoding tyrosinase, the enzyme that catalyzes the first 2 steps of melanin pigment biosynthesis. In type IA (tyrosinase-negative) OCA tyrosinase enzymatic activity is completely absent, and in type IB ("yellow") OCA tyrosinase activity is greatly reduced. Here, we describe 11 novel mutations of the tyrosinase gene in Caucasian patients with these 2 forms of type I OCA. Type I OCA in Caucasians appears to result from a great variety of different uncommon alleles. More than 80% of the known missense substitutions associated with type I OCA cluster within 2 relatively small regions of the tyrosinase polypeptide, suggesting that these may correspond to functionally important sites within the enzyme.
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PMID:Tyrosinase gene mutations in type I (tyrosinase-deficient) oculocutaneous albinism define two clusters of missense substitutions. 164 78

We have identified a common nonpathological polymorphism of the human tyrosinase gene. In Caucasians codon 402 can be either CGA (arginine) [p = .85] or CAA (glutamine) [p = .15]. This polymorphism also occurs in American Blacks, but the codon 402CAA (Gln) allele was not detected in Oriental populations. The substitution of glutamine for arginine at codon 402 results in moderate thermoinstability of the corresponding tyrosinase polypeptide. Tyrosinase enzymatic activity expressed in HeLa cells transfected with a codon 402Gln tyrosinase cDNA is reduced by approximately 75 percent when cells are cultured at 37 degrees C as compared to 31 degrees C, whereas enzymatic activity of codon 402Arg tyrosinase is not temperature-sensitive. However, the genotype at codon 402 of tryosinase is not correlated with the apparent pigmentation phenotype in normal Caucasians.
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PMID:A polymorphism of the human tyrosinase gene is associated with temperature-sensitive enzymatic activity. 182 Feb 7

We detected a nonsense mutation in the tyrosinase gene of two Afghan sibs with classical tyrosinase negative (type IA) oculocutaneous albinism. The mutation, a single base substitution at codon 178, creates an amber termination codon that truncates the 529 amino acid tyrosinase polypeptide at this position. The patients' parents are first cousins, and the patients are therefore homoallelic for this mutation.
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PMID:A nonsense mutation in the tyrosinase gene of Afghan patients with tyrosinase negative (type IA) oculocutaneous albinism. 183 18

We have identified a tyrosinase gene mutation in an American black with classic, tyrosinase-negative oculocutaneous albinism. This mutation results in an amino acid substitution (Cys----Arg) at codon 89 of the tyrosinase polypeptide. The proband is homozygous for the substitution, suggesting that this mutation may be frequently associated with tyrosinase-negative oculocutaneous albinism in blacks.
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PMID:Homozygous tyrosinase gene mutation in an American black with tyrosinase-negative (type IA) oculocutaneous albinism. 189 21

Type I oculocutaneous albinism (OCA) is an autosomal recessive disorder in which deficient synthesis of melanin pigment results from abnormal activity of melanocyte tyrosinase. A novel type I OCA phenotype in which hypopigmentation is related to local body temperature is associated with a missense substitution in tyrosinase, codon 422 CGG (Arg)----CAG (Gln). This substitution results in a tyrosinase polypeptide that is temperature-sensitive. This form of type I OCA thus is homologous to the temperature-related forms of albinism seen in the Siamese cat and the Himalayan mouse.
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PMID:A tyrosinase gene missense mutation in temperature-sensitive type I oculocutaneous albinism. A human homologue to the Siamese cat and the Himalayan mouse. 190 Mar 9

We have identified a tyrosinase gene mutation in several patients with classic, tyrosinase-negative (type IA) oculocutaneous albinism. This mutation, which results in a proline----leucine substitution at codon 81 of the tyrosinase polypeptide (EC 1.14.18.1), was observed in 20% (6 of 30) of oculocutaneous albinism alleles from independent probands, but it was not observed in any normal individuals. This mutation thus appears to be a frequent cause of tyrosinase-negative oculocutaneous albinism.
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PMID:A frequent tyrosinase gene mutation in classic, tyrosinase-negative (type IA) oculocutaneous albinism. 197 Jun 34


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