Topic
Tyrosinase
About: Tyrosinase is a research topic. Over the lifetime, 7244 publications have been published within this topic receiving 197919 citations. The topic is also known as: tyrosinase & monophenol oxygenase.
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TL;DR: Constitutive generation of large amounts of reactive oxygen intermediates, if it occurs in vivo, might contribute to the ability of some tumors to mutate, inhibit antiproteases, injure local tissues, and therefore promote tumor heterogeneity, invasion, and metastasis.
Abstract: Few nonphagocytic cells are known to generate reactive oxygen intermediates. Based on horseradish peroxidase-dependent, catalase-inhibitable oxidation of fluorescent scopoletin, seven human tumor cell lines constitutively elaborated H2O2 at rates (up to 0.5 nmol/10(4) cells/h) large enough that cumulative amounts at 4 h were comparable to the amount of H2O2 produced by phorbol ester-triggered neutrophils. Superoxide dismutase-inhibitable ferricytochrome c reduction was detectable at much lower rates. H2O2 production was inhibited by diphenyleneiodonium, a flavoprotein binder (concentration producing 50% inhibition, 0.3 microM), and diethyldithiocarbamate, a divalent cation chelator (concentration producing 50% inhibition, 3 microM), but not by cyanide or azide, inhibitors of electron transport, or by agents that inhibit xanthine oxidase, polyamine oxidase, or cytochrome P450. Cytochrome b559, present in human phagocytes and lymphocytes, was undetectable in these tumor cells by a sensitive spectrophotometric method. Mouse fibroblasts transfected with human tyrosinase complementary DNA made melanin, but not H2O2. Constitutive generation of large amounts of reactive oxygen intermediates, if it occurs in vivo, might contribute to the ability of some tumors to mutate, inhibit antiproteases, injure local tissues, and therefore promote tumor heterogeneity, invasion, and metastasis.
2,417 citations
TL;DR: This article surveys tyrosinase inhibitors newly discovered from natural and synthetic sources and the inhibitory strength is compared with that of a standard inhibitor, kojic acid, and their inhibitory mechanisms are discussed.
Abstract: Tyrosinase is a multifunctional, glycosylated, and copper-containing oxidase, which catalyzes the first two steps in mammalian melanogenesis and is responsible for enzymatic browning reactions in damaged fruits during post-harvest handling and processing. Neither hyperpigmentation in human skin nor enzymatic browning in fruits are desirable. These phenomena have encouraged researchers to seek new potent tyrosinase inhibitors for use in foods and cosmetics. This article surveys tyrosinase inhibitors newly discovered from natural and synthetic sources. The inhibitory strength is compared with that of a standard inhibitor, kojic acid, and their inhibitory mechanisms are discussed.
1,200 citations
1,117 citations
TL;DR: This article overviews the various inhibitors obtained from natural and synthetic sources with their industrial importance, and examines the role of tyrosinase in melanin biosynthesis and its role in dermatological disorders.
Abstract: Tyrosinase is known to be a key enzyme in melanin biosynthesis, involved in determining the color of mammalian skin and hair. Various dermatological disorders, such as melasma, age spots and sites of actinic damage, arise from the accumulation of an excessive level of epidermal pigmentation. In addition, unfavorable enzymatic browning of plant-derived foods by tyrosinase causes a decrease in nutritional quality and economic loss of food products. The inadequacy of current conventional techniques to prevent tyrosinase action encourages us to seek new potent tyrosinase inhibitors. This article overviews the various inhibitors obtained from natural and synthetic sources with their industrial importance.
913 citations
TL;DR: Three additional discoveries have increased interest among plant pathologists in fungal melanins, including a new class of fungicides that prevent direct penetra tion of plant tissue by inhibiting melanin biosynthesis in appressorial cells.
Abstract: Melanins are dark-brown to black pigments found in animals, plants, and microorganisms. These pigments are not essential for growth and develop ment, but rather they enhance the survival and competitive abilities of species in certain environments. The association of melanins with immune responses has been noted for plants (13) and invertebrates (180, 227, 239, 250). Melanin biosynthesis and function have been studied most extensively in animals, primarily because of the association of melanins with skin disorders (25,53, 188) and malignant melanomas (119). Melanins in the eye and inner ear have also received considerable attention because of their interactions with drugs (84). The synthesis of animal melanin from tyrosine by the action of tyrosinase is proven (52, 175, 270). Tyrosinase, the key enzyme in animal melanin synthesis, also occurs and is best characterized in the common mushroom (Agaricus bisporus) and Neurospora crassa (136). Consequently, some researchers have been hasty to conclude that fungal melanins also are derived from tyrosine. The importance of melanins for survival and longevity of fungal propagules has been recognized for many years (126, 235). During the past ten years three additional discoveries have increased interest among plant pathologists in fungal melanins. First, unique pathways for melanin biosynthesis were discovered in both Ascomycotina (16) and Basidiomycotina (234). Second, investigators discovered a new class of fungicides that prevent direct penetra tion of plant tissue by inhibiting melanin biosynthesis in appressorial cells (221, 223). Third, phytotoxins were discovered that are shunt products of
897 citations