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At least 19 recordsLinked to original sources
PubMed1975

Monophenol monooxygenase and lincomysin biosynthesis in Streptomyces lincolnensis.

Monophenol monooxygenase (monophenol, dihydroxyphenylalanine:oxygen oxidoreductase EC 1.14.18.1) was studied in melanin-positive and melanin-negative mutants of Streptomyces lincolnensis NCIB 9413, varying in the lincomycin synthesizing ability. The activities of laccase and tyrosine phenol lyase (EC 4.1.99.2) are absent in this organism. The monophenol monooxygenase catalyzes hydroxylation of monophenols (K(m) and V(max) for l-tyrosine, 2 x 10(-4) M and 8.0 nmol of O(2)/min per ml, respectively) at a slower rate than it dehydrogenates diphenols to o-quinones (K(m) and V(max) for l-3,4-dihydroxyphenylalanine, 7 x 10(-5) M and 51.7 nmol of O(2)/min per ml, respectively. It is inhibited by KCN, beta-mercaptoethanol, ethylenediaminetetraacetate, dipyridyl, thiourea, p-aminobenzoic acids and by some tryptophan metabolites. Changes in the activity of monophenol monooxygenase caused by mutation or by inhibitors are reflected in the synthesis of the antibiotic. Its participation in the biogenesis of the propylhygric moiety of lincomycin is discussed.

Amino Acids↗
PubMed1989

Stereochemical studies on the formation of melanin by monophenol monooxygenase.

The oxidation of tyrosine by monophenol monooxygenase (tyrosinase: EC 1.10.3.1) to melanin has been studied by a combination of ultraviolet, circular dichroism, and nuclear magnetic resonance techniques. It is demonstrated that the chiral intermediate (dopachrome) is generated stereoselectively in this enzymic reaction.

Catechol Oxidase↗
PubMedDate not supplied

[Intracellular localization and characteristics of monophenol monooxygenase in the leaves of tea plants].

The intracellular localization and some properties of monophenol monooxygenase (MPMO) from fresh tea leaves have been studied. It has been demonstrated that MPMO activity is located in cytosole and chloroplasts. These two forms have different properties. Molecular weights of cytosole and chloroplasts MPMO are 41 and 28 kD respectively. The chloroplasts and cytosole forms of MPMO reveal maximum activity at pH 5.3 and 7.1 respectively.

Cytosol↗
PubMed1988

Tyrosinases of murine melanocytes with mutations at the albino locus.

Tyrosinase (monophenol monooxygenase; monophenol, L-dopa:oxygen oxidoreductase, EC 1.14.18.1) is a key enzyme in the synthesis of melanin. Reduced levels of tyrosinase play an important role in albinism. The data described here show differences in the expression and characteristics of tyrosinase in cutaneous murine melanocytes grown in culture from normal wild-type strains (C/C); from three albino locus mutants: himalayan (ch/ch), chinchilla (cch/cch), and albino (c/c); and from the double-mutant heterozygous pink-eyed chinchilla (cchp/cp). Our results suggest that the diminished pigmentation in all mutants is due to abnormal posttranslational modification of the enzyme: the levels of mRNA for tyrosinase in wild-type, himalayan, and pink-eyed chinchilla melanocytes are similar; the himalayan mutation confers a deficiency in N-linked glycosylation, which results in an extremely unstable enzyme that is also temperature sensitive; the chinchilla and albino mutations confer susceptibility to proteolytic cleavage; the pink-eye dilution confers a reduction in the levels of immunoprecipitable tyrosinase, and what little enzyme there is fails to be translocated from the trans-Golgi network to melanosomes. The kinetics of activation and inhibition of the enzyme by the cofactor dopa are unique for the mutants tested and differ from those of tyrosinase from wild-type melanocytes. The findings support the conclusion that the albino locus in mice encodes the structural gene of tyrosinase.

Animals↗
PubMed1990

Murine and human b locus pigmentation genes encode a glycoprotein (gp75) with catalase activity.

Melanogenesis is regulated in large part by tyrosinase (monophenol monooxygenase; monophenol, L-dopa:oxygen oxidoreductase, EC 1.14.18.1), and defective tyrosinase leads to albinism. The mechanisms for other pigmentation determinants (e.g., those operative in tyrosinase-positive albinism and in murine coat-color mutants) are not yet known. One murine pigmentation gene, the brown (b) locus, when mutated leads to a brown (b/b) or hypopigmented (Blt/Blt) coat versus the wild-type black (B/B). We show that the b locus codes for a glycoprotein with the activity of a catalase (hydrogen-peroxide:hydrogen-peroxide oxidoreductase, EC 1.11.1.6) (catalase B). Only the c locus protein is a tyrosinase. Because peroxides may be by-products of melanogenic activity and hydrogen peroxide in particular is known to destroy melanin precursors and melanin, we conclude that pigmentation is controlled not only by tyrosinase but also by a hydroperoxidase. Our studies indicate that catalase B is identical with gp75, a known human melanosomal glycoprotein; that the b mutation is in a heme-associated domain; and that the Blt mutation renders the protein susceptible to rapid proteolytic degradation.

Albinism↗
PubMed1991

The mouse tyrosinase promoter is sufficient for expression in melanocytes and in the pigmented epithelium of the retina.

The mouse c locus encodes tyrosinase (monophenol monooxygenase; monophenol, L-dopa:oxygen oxidoreductase, EC 1.14.18.1), the key enzyme in melanin synthesis, which is expressed in the pigment epithelium of the retina and in melanocytes derived from the neural crest. To define regulatory regions of the gene that are important for cell type-specific expression, a deletion series of the tyrosinase 5' region was fused to a chloramphenicol acetyltransferase (CAT) reporter gene and electroporated into tyrosinase-expressing and -nonexpressing cell lines. We show that 270 base pairs 5' of the transcriptional start site is sufficient for CAT expression in a human and a mouse melanoma cell line. This 5' flanking fragment, when cloned in the context of a tyrosinase minigene construct and injected into fertilized eggs of an albino mouse strain, is sufficient for cell type-specific expression in mice. The transgenic mice were pigmented in both skin and eyes. In situ hybridization analysis shows that the 270-base-pair regulatory region contains elements sufficient for specific expression of the transgene both in the pigmented epithelial cells of the retina, which are derived from the optic cup, and in neural crest-derived melanocytes.

Animals↗
PubMed1975

Melanoma cells resistant to inhibition of growth by melanocyte stimulating hormone.

Melanocyte stimulating hormone (MSH) enhances melanization but inhibits proliferation of Cloudman S91 melanoma cells in culture. We have isolated variants of these cells that can grow in the presence of MSH. The conclusions we have reached from analyses of these cells are the following: (1) Basal tyrosinase activity (monophenol monooxygenase; monophenol, dihydroxyphenylalanine:oxygen oxidoreductase, EC 1.14.18.1), i.e., the activity that is present in the absence of added MSH, is related through a common biochemical pathway to MSH-mediated control of growth. (2) MSH-inducible tyrosinase activity does not appear to be related to MSH control of growth. (3) The morphological changes that occur following the addition of MSH or cAMP are related to controls of growth and not to those of melanization.

Animals↗
PubMed1978

Reductant-dependent electron distribution among redox sites of laccase.

Rhus laccase (monophenol monooxygenase, monophenol,dihydroxyphenylalanine:oxygen oxidoreductase, EC 1.14.18.1) an O2/H2O oxidoreductase containing four copper ions bound to three redox sites (type 1, type 2, and type 3 Cu pair), was titrated anaerobically with several reductants having various chemical and thermodynamic properties. The distribution of electron equivalents among the redox sites was found to be reductant dependent. When the data for titration by various reductants of the type 3 site were plotted against those of the type 1 site according to the Nernst formalism, the slope n varied from 2.0 to 1.0. The redox potential of the reductant's first oxidation step is qualitatively correlated with the value of n and is suggested as the factor that modulates the electron distribution. Such a behavior implies a nonequilibrium situation. A very good simulation of the data was provided by an analysis assuming a formally variable cooperativity between the two type 3 copper ions. This apparent variability is suggested to result from a process whereby sufficiently strong reductants induce a transition of the type 3 site from a cooperative two-electron acceptor to a pair of independent one-electron acceptors. This uncoupled state of the type 3 site is considered metastable. Other possible models were also investigated. Summarizing the available data, we conclude that the two-electron accepting behavior of the 330-nm chromophore is the exception rather than the rule.

Anaerobiosis↗
PubMedDate not supplied

[Study of availability of some hydrolytic and redox enzymes in strains of Fusarium oxysporum (Schlecht.) Snyd. and Hans. isolated from different habitats].

The work authors have used 52 strains of F. oxysporum for the collection of cultures of the Department of Physiology and Taxonomy of Micromycetes of IMV of the NAS of Ukraine. The strains were isolated from three habitats--grain cultures, cultivated and noncultivated soils of different regions of Ukraine. Activity of some hydrolytic (cellulose, endo-1,4-beta-xylanase, beta-glucosidase and amylase) and redox (monophenol-monooxygenase and peroxidase) enzymes of F. oxysporum strains. It has been shown that strains isolated from plant substrates produced more actively hydrolytic enzymes--cellulose, endo-1,4-beta-xylanase and beta-glucosidase. As to the degree of these enzymes activity the studied strains were distributed in the following order: strains from plants (P) > strains from cultivated soil (CS) > strains from noncultivated soils (NS). The soil strains NS > CS > P proved to be more active as to activity manifestation of the redox enzymes (monophenol-monooxygenase and peroxidase).

Fusarium↗
PubMed1997

Phenol-oxidizing enzymes: mechanisms and applications in biosensors.

Phenolic compounds are widely distributed in nature. Enzymes which catalyze their oxidation are monophenol monooxygenases, such as tyrosinases and laccases, and peroxidases. Their metabolic role includes the decomposition of natural complex aromatic polymers as well as polymerization of the oxidation products and the degradation of xenobiotics. Their catalytic properties and broad availability gained impact on the development of biosenors for both environmentally important pollutants and clinically relevant metabolites. Mechanisms for the phenol-oxidizine enzymes tyrosinases, laccases, and peroxidases are reviewed and some examples for their use in the construction of phenol selective biosenors are given.

Biosensing Techniques↗
PubMed2002

Comparative biochemistry of eumelanogenesis and the protective roles of phenoloxidase and melanin in insects.

The phenolic biopolymer eumelanin is an important skin pigment found throughout the animal kingdom. The enzyme, tyrosinase, initiates melanogenesis in mammals. The biogenesis is assisted by a number of mammalian protein factors including dopachrome tautomerase and 5,6-dihydroxyindole-2-carboxylate oxidase. Invertebrates, such as insects, employ phenoloxidase and dopachrome (decarboxylating) isomerase for melanin biosynthesis. Recently generated molecular biological and biochemical data indicate that tyrosinase and phenoloxidase are distinctly different enzymes in spite of possessing both monophenol monooxygenase activity as well as o-diphenoloxidase activity. Similarly, insect dopachrome isomerase also differs significantly from its mammalian counterpart in several of its properties including the nature of the enzymatic reaction. In addition, there are considerable differences in the eumelanogenic pathways of these two animal groups that include the utility of substrates, use of dihydroxyindoles and the nature of eumelanin pigment. Thus, the biochemistry and molecular biology of melanogenesis in mammals and insects are significantly different. The advantages of generating different eumelanin pigments and intermediates by the insects are discussed.

Amino Acid Sequence↗
PubMed1999

Inhibition of tyrosinase by green tea components.

The pigment melanin in human skin is a major defense mechanism against ultraviolet light of the sun, but darkened skin color, which is the result of increased and redistributed epidermal melanin, could be a serious aesthetic problem. Epidemiologically, it is well known that the consumption of green tea may help prevent cancers in humans and also reduce several free radicals including peroxynitrite. In the present study, to assess the efficacy of the inhibition of mushroom tyrosinase (monophenol monooxygenase EC 1.14.18.1), ten kinds of Korean traditional teas were screened for their tyrosinase inhibitory activity. Green tea was the strongest inhibitor, and the major active constituents in the tea are (-)-epicatechin 3-O-gallate (ECG), (-)-gallocatechin 3-O-gallate (GCG), and (-)-epigallocatechin 3-O-gallate (EGCG). All are catechins with gallic acid group as an active site. The kinetic analysis for inhibition of tyrosinase revealed a competitive nature of GCG with this enzyme for the L-tyrosine binding at the active site of tyrosinase.

Agaricales↗
PubMed1985

In vitro studies of 2,4-dihydroxyphenylalanine, a prodrug targeted against malignant melanoma cells.

We have evaluated the chemotherapeutic potential of 2,4-dihydroxyphenylalanine, a targeted prodrug that can be hydroxylated by tyrosinase (monophenol monooxygenase, EC 1.14.18.1) within melanoma cells to form the cellular toxin 2,4,5-trihydroxyphenylalanine (6-hydroxydopa). 2,4-Dihydroxyphenylalanine proved to be cytotoxic to both B-16 and Cloudman melanoma cells in vitro. The immediate effects of 2,4-dihydroxyphenylalanine included inhibition of DNA, RNA, and protein syntheses. In contrast, no decrease in macromolecular synthesis or viability was seen against cultures of MJY-alpha mammary tumor or L-1210 leukemia, two cell types that do not contain tyrosinase. Within the melanoma cultures, greater cytotoxicity was seen against melanotic (tyrosinase-containing) cells than against amelanotic (tyrosinase-lacking) cells. The cytotoxicity of 2,4-dihydroxyphenylalanine was blocked by 1-phenylthiourea, an inhibitor of tyrosinase. These results show that 2,4-dihydroxyphenylalanine is toxic to melanoma cells and that activation of 2,4-dihydroxyphenylalanine requires the presence of tyrosinase.

Animals↗
PubMed1981

Tyrosinase activity and isoenzyme distribution corresponding to growth and regression of melanoma in Sinclair miniature swine.

Malignant melanomas have been shown to contain high levels of monophenol monooxygenase (tyrosinase) enzyme activity; the enzyme is responsible for melanin synthesis. The melanoma of Sinclair miniature swine has a high incidence of spontaneous regression and thus provides a unique system for analyzing changes in tyrosinase activity at various tumor stages. Three tumor stages (progressively growing tumors, partially regressed tumors, and fully regressed tumors) were analyzed for tyrosinase activity. The progressing tumors were 34-fold higher than were the partially regressed lesions and 400-fold higher than were the fully regressed tumors. Histologically, the decrease in enzyme activity correlated with a loss of tumor cells. Sequential biopsies of tumors during the course of tumor development showed a positive correspondence between tumor volume and tyrosinase activity for the early and late stages of tumor growth and regression. Electrophoretic separation of tyrosinase preparations revealed three major tyrosinase "isoenzymes" whose relative abundance fluctuated during developmental increases and decreases in enzyme activity.

Age Factors↗
PubMed2006

Extraction and partial characterization of polyphenol oxidase from banana (Musa acuminata Grande naine) roots.

Polyphenol oxidase activity (PPO, EC 1.14.18.1, monophenol monooxygenase, and EC 1.10.3.2, o-diphenoloxidase) has been extensively studied in banana fruit for its role in enzymatic browning. Rapid discolouration of leaf, stem and root tissue after injury and strong pigmentation of tissue extracts indicate that PPO and phenolic compounds are ubiquitous in vegetative tissue of banana as well. They hamper biochemical and molecular studies in banana, as cumbersome adaptations of extraction protocols are required. On the other hand, PPO and phenolic compounds could be an important part of the plant's defence system against pests and diseases, including root parasitic nematodes. To facilitate future studies in this area, extraction and assay conditions for PPO from roots of banana (Musa acuminata AAA, Grande naine) were optimized. Highest enzyme activities were obtained in a 0.2 M phosphate buffer at pH 7.0 with 5% insoluble polyvinylpyrrolidone and 0.25% Triton X-100. The lowest K(m) values were obtained for dopamine and D-catechin. Monophenolase activity was shown with p-cresol. Banana root PPO was strongly inhibited by dithiothreitol and sodium metabisulfite. In root sections, oxidation of dopamine strongly co-localized with aerenchyma in the cortex. The experiments revealed indications for the involvement of root PPO and dopamine in resistance of banana against the parasitic nematode Radopholus similis.

Catechin↗
PubMed1998

Laccase--and not tyrosinase--is the enzyme responsible for quinone methide production from 2,6-dimethoxy-4-allyl phenol.

Tyrosinase, which is known to possess both monophenol monooxygenase activity (EC 1.14.18.1, tyrosine, 3,4-dihydroxyphenylalanine:oxygen oxidoreductase) and o-diphenoloxidase activity (EC 1.10.3.1, o-diphenol:oxygen oxidoreductase), has been shown to exhibit other related activities. Recently, a new reaction, viz., oxidative conversion of 2,6-dimethoxyallyl phenol to its quinone methide, catalyzed by commercial preparations of mushroom tyrosinase was reported (E. S. Krol, and J. L. Bolton, 1997, Chem. Biol. Interact. 104, 11-27). Since the reaction involves an unusual 1,6-oxidation rather than the conventional 1,4-oxidation, we reexamined this reaction more carefully. The o-diphenoloxidase activity and the dimethoxyallyl phenol oxidase activity of mushroom tyrosinase preparations exhibited different mobilities on size-exclusion chromatography on a Sephacryl S-200 column. A similar behavior was also witnessed on preparative isoelectric focusing in a rotofor cell. Different preparations of mushroom tyrosinase possessed varying ratios of these two activities, further confirming that they are due to two different enzymes. Native polyacrylamide gel electrophoresis followed by activity staining of the gel revealed different mobilities for these two activities. The protein band exhibiting dimethoxyallyl phenol oxidase activity could also be stained by syringaldazine, a well-known substrate for laccase (EC 1.10.3.2, p-diphenol:oxygen oxidoreductase). Two insect phenoloxidases, which are known for their wide substrate specificity, failed to oxidize dimethoxyallyl phenol to any detectable extent, thereby confirming that typical o-diphenoloxidases lack the ability to oxidize dimethoxyallyl phenol. On the other hand, laccase, which is known to convert syringaldazine to its quinone methide derivative, readily produced the quinone methide from dimethoxyallyl phenol. It is therefore concluded that laccase, which is present as a contaminant in the commercial preparations of mushroom tyrosinase--and not tyrosinase (o-diphenoloxidase)--is the enzyme responsible for catalyzing the new conversion of dimethoxyallyl phenol to its corresponding quinone methide.

Basidiomycota↗