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We investigate the melanin biosynthesis stimulatory

N2 - Melanins are hydrophobic polymers of high molecular weight, formed by oxidative polymerization of phenolic and indolic compounds, produced by organisms in all Kingdoms. They are typically black or dark brown in color and their molecular structures are diverse. Several fungi can produce melanins and the functions of this pigment enhance microbial survival under diverse unfavorable environmental and host conditions. The major melanin type encountered among fungi is the 1,8-dihydroxynaphthalene (DHN) melanin that is synthesized from acetyl-coenzyme A via the polyketide pathway. This melanin is generated by several human pathogenic fungi, such as Fonsecaea pedrosoi, Exophialla dermatitidis, Aspergillus fumigatus, Histoplasma capsulatum and Sporothrix schenckii. It is also present in phytopathogenic fungi such as Colletotrichum spp., Magnaporte orizae and Ascochyta rabiei. In addition to DHN melanin, fungi can also produce melanin via dihydroxyphenylalanine (DOPA), in which tyrosinases or laccases hydroxylate tyrosine via DOPA to dopaquinone that then auto-oxidizes and polymerizes, resulting in a polyphenolic heteropolymer of black color known as eumelanin. Cryptococcus neoformans is the best known fungus to produce this type of melanin, but other fungi such as Candida albicans, Paracoccidioides brasiliensis and S. schenckii can also produce eumelanin. A type of soluble fungal melanin is produced from L-tyrosine through p-hydroxyphenylpyruvate and homogentisic acid. This pigment is called pyomelanin and it is similar to alkaptomelanin produced by humans. A. fumigatus, Madurella mycetomatis and Yarrowia lipolytica are examples of fungi that can produce this type of pigment. Fungal melanins play an important role in the protection of fungi from several environmental stresses, such as desiccation, UV irradiation, heavy metals, temperature fluctuation and digestion by hydrolytic enzymes. Melanins also play a role in the virulence of a broad range of pathogenic fungi. These pigments protect the fungi from host defense mechanisms and antifungal agents. Although melanins challenge the immunological strategies of host defense, they are also targets for alternative antimicrobial strategies, by the use of antibodies against melanin or inhibitors of melanin synthesis.

BT - Melanin: Biosynthesis, Functions and Health Effects

Ballotti (1996) Ultraviolet B radiation acts through the nitric oxide and cGMP signal transduction pathway to stimulate melanogenesis in human melanocytes.

(1955) Glutathione inhibition of melanin synthesis in vitro.

Hearing (1993) Melanin biosynthesis patterns of following hormonal stimulation.

IUBMB Life. 2013. Phenylalanine hydroxylase: function, structure, and regulation. Mammalian phenylalanine hydroxylase (PAH) catalyzes the rate-limiting step in the phenylalanine catabolism, consuming about 75% of the phenylalanine input from the diet and protein catabolism under physiological conditions. In humans, mutations in the PAH gene lead to phenylketonuria (PKU), and most mutations are mainly associated with PAH misfolding and instability. The established treatment for PKU is a phenylalanine-restricted diet and, recently, supplementation with preparations of the natural tetrahydrobiopterin cofactor also shows effectiveness for some patients. Since 1997 there has been a significant increase in the understanding of the structure, catalytic mechanism, and regulation of PAH by its substrate and cofactor, in addition to improved correlations between genotype and phenotype in PKU. Importantly, there has also been an increased number of studies on the structure and function of PAH from bacteria and lower eukaryote organisms, revealing an additional anabolic role of the enzyme in the synthesis of melanin-like pigments. In this review, we discuss these recent studies, which contribute to define the evolutionary adaptation of the PAH structure and function leading to sophisticated regulation for effective catabolic processing of phenylalanine in mammalian organisms.

Inhibitors of melanin biosynthesis from marine microalgae were screened against a melanin-producing microorganism, Streptomyces bikiniensis. From 28 marine microalgal strains, 5 were found showing inhibitory activity. Of these, the extracts (50μl, 2μg total organic carbon/μl) from two marine green algae showed strongly inhibited melanin biosynthesis, but showed less than 30 % inhibitory activity against mushroom tyrosinase.

In humans, melanin is the primary determinant of skin color

AB - Melanins are hydrophobic polymers of high molecular weight, formed by oxidative polymerization of phenolic and indolic compounds, produced by organisms in all Kingdoms. They are typically black or dark brown in color and their molecular structures are diverse. Several fungi can produce melanins and the functions of this pigment enhance microbial survival under diverse unfavorable environmental and host conditions. The major melanin type encountered among fungi is the 1,8-dihydroxynaphthalene (DHN) melanin that is synthesized from acetyl-coenzyme A via the polyketide pathway. This melanin is generated by several human pathogenic fungi, such as Fonsecaea pedrosoi, Exophialla dermatitidis, Aspergillus fumigatus, Histoplasma capsulatum and Sporothrix schenckii. It is also present in phytopathogenic fungi such as Colletotrichum spp., Magnaporte orizae and Ascochyta rabiei. In addition to DHN melanin, fungi can also produce melanin via dihydroxyphenylalanine (DOPA), in which tyrosinases or laccases hydroxylate tyrosine via DOPA to dopaquinone that then auto-oxidizes and polymerizes, resulting in a polyphenolic heteropolymer of black color known as eumelanin. Cryptococcus neoformans is the best known fungus to produce this type of melanin, but other fungi such as Candida albicans, Paracoccidioides brasiliensis and S. schenckii can also produce eumelanin. A type of soluble fungal melanin is produced from L-tyrosine through p-hydroxyphenylpyruvate and homogentisic acid. This pigment is called pyomelanin and it is similar to alkaptomelanin produced by humans. A. fumigatus, Madurella mycetomatis and Yarrowia lipolytica are examples of fungi that can produce this type of pigment. Fungal melanins play an important role in the protection of fungi from several environmental stresses, such as desiccation, UV irradiation, heavy metals, temperature fluctuation and digestion by hydrolytic enzymes. Melanins also play a role in the virulence of a broad range of pathogenic fungi. These pigments protect the fungi from host defense mechanisms and antifungal agents. Although melanins challenge the immunological strategies of host defense, they are also targets for alternative antimicrobial strategies, by the use of antibodies against melanin or inhibitors of melanin synthesis.

N2 - Inhibitors of melanin biosynthesis from marine microalgae were screened against a melanin-producing microorganism, Streptomyces bikiniensis. From 28 marine microalgal strains, 5 were found showing inhibitory activity. Of these, the extracts (50μl, 2μg total organic carbon/μl) from two marine green algae showed strongly inhibited melanin biosynthesis, but showed less than 30 % inhibitory activity against mushroom tyrosinase.

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Fungal melanins : Biosynthesis and biological functions

Topics include melanogenesis and natural hypopigmentation agents; fungal melanins; the coat color genes that regulate eumelanin and pheomelanin synthesis in melanocytes; the role of melanin production in gaeumannomyces graminis infection of cereal plants and the occurrence and function of melanic pigmentation in ectothermic vertebrates.

Melanin: Biosynthesis, Functions and Health Effects

AB - Melanins serve a variety of protective functions in plants and animals, but in fungi such as Cryptococcus neoformans they are also associated with virulence. A recently developed solid-state nuclear magnetic resonance (NMR) strategy, based on the incorporation of site-specific 13C-enriched precursors into melanin, followed by spectroscopy of both powdered and solvent-swelled melanin ghosts, was used to provide new molecular-level insights into fungal melanin biosynthesis. The side chain of an L-dopa precursor was shown to cyclize and form a proposed indole structure in C. neoformans melanin, and modification of the aromatic rings revealed possible patterns of polymer chain elongation and cross-linking within the biopolymer. Mannose supplied in the growth medium was retained as a β-pyranose moiety in the melanin ghosts even after exhaustive degradative and dialysis treatments, suggesting the possibility of tight binding or covalent incorporation of the pigment into the polysaccharide fungal cell walls. In contrast, glucose was scrambled metabolically and incorporated into both polysaccharide cell walls and aliphatic chains present in the melanin ghosts, consistent with metabolic use as a cellular nutrient as well as covalent attachment to the pigment. The prominent aliphatic groups reported previously in several fungal melanins were identified as triglyceride structures that may have one or more sites of chain unsaturation. These results establish that fungal melanin contains chemical components derived from sources other than L-dopa polymerization and suggest that covalent linkages between L-dopa-derived products and polysaccharide components may serve to attach this pigment to cell wall structures.

Melanin Biosynthesis in Cryptococcus neoformans …

AB - Inhibitors of melanin biosynthesis from marine microalgae were screened against a melanin-producing microorganism, Streptomyces bikiniensis. From 28 marine microalgal strains, 5 were found showing inhibitory activity. Of these, the extracts (50μl, 2μg total organic carbon/μl) from two marine green algae showed strongly inhibited melanin biosynthesis, but showed less than 30 % inhibitory activity against mushroom tyrosinase.

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