Search results for "melanin."
showing 10 items of 68 documents
Imaging of Substantia Nigra in Parkinson's Disease: A Narrative Review.
2021
Parkinson’s disease (PD) is a progressive neurodegenerative disorder, characterized by motor and non-motor symptoms due to the degeneration of the pars compacta of the substantia nigra (SNc) with dopaminergic denervation of the striatum. Although the diagnosis of PD is principally based on a clinical assessment, great efforts have been expended over the past two decades to evaluate reliable biomarkers for PD. Among these biomarkers, magnetic resonance imaging (MRI)-based biomarkers may play a key role. Conventional MRI sequences are considered by many in the field to have low sensitivity, while advanced pulse sequences and ultra-high-field MRI techniques have brought many advantages, partic…
Pigmented odontogenic keratocyst : report of a rare case and review of the literature
2018
Pigmented odontogenic keratocyst (OKC) is very rare and its etiology remains uncertain. To the best of our knowledge, only 9 cases of pigmented OKC have been published in English-language literature. This report describes a pigmented OKC in a 14-year-old black male patient. Radiographically, the lesion appeared as a well-circumscribed, unilocular, and radiolucent image. A surgical excision was performed. Histopathological examination revealed an OKC. Additionally, a brownish, sparsed, intracytoplasmic pigmentation was observed in the basal cell layer, which was positive for Fontana-Masson staining. Immunohistochemistry reactions revealed positive dendritic cells for S-100 protein, HMB45 and…
Prediction of tyrosinase inhibition activity using atom-based bilinear indices.
2007
A set of novel atom-based molecular fingerprints is proposed based on a bilinear map similar to that defined in linear algebra. These molecular descriptors (MDs) are proposed as a new means of molecular parametrization easily calculated from 2D molecular information. The nonstochastic and stochastic molecular indices match molecular structure provided by molecular topology by using the kth nonstochastic and stochastic graph-theoretical electronic-density matrices, M(k) and S(k), respectively. Thus, the kth nonstochastic and stochastic bilinear indices are calculated using M(k) and S(k) as matrix operators of bilinear transformations. Chemical information is coded by using different pair com…
Formation of melanin-based wing patterns is influenced by condition and immune challenge in Pieris brassicae
2005
According to life-history theory, trade-offs emerge because organisms possess a limited amount of resources that they have to allocate between different bodily functions. Here, we tested whether there is a trade-off between melanin-based immune response and dark melanized wing patterning in the large white butterfly, Pieris brassicae L. (Lepidoptera: Pieridae), by activating the immune system of pupae and measuring the wing pigmentation of freshly emerged adults. In contrast to expectations, we did not find any negative associations between immune challenge and wing patterning. Furthermore, implanted and punctured male pupae tended to have larger and darker forewing tips as adults compared …
Biocatalytic formation of synthetic melanin: The role of vanadium haloperoxidases, L-DOPA and iodide
2011
The vanadium haloperoxidase (V-HPO) enzyme, extracted from the brown alga Laminaria saccharina, is able to catalyze the formation of a black precipitate, using as precursor the amino acid L-dopa in the presence of hydrogen peroxide and iodide, in one-pot synthesis. The L-dopa oxidation is a multistep reaction with a crucial role played by the iodide in the enzyme catalyzed peroxidative production of dopachrome, a well known intermediate in the synthesis of melanin. Dopachrome is then converted to a synthetic form of melanin through a polymerization reaction. Factors, such as buffer composition and pH, influence significantly the reaction first steps, but further steps of melanin production …
The Recent Crystal Structure of Human Tyrosinase Related Protein 1 (HsTYRP1) Solves an Old Problem and Poses a New One
2017
Show your metal: l-Tyrosine is converted into the protective antioxidative polymer melanin in a sequence of reactions. In humans, the catalytic pathway starts with the tyrosinase HsTYR and two tyrosinase-related proteins HsTYRP1 and HsTYRP2. All three enzymes have the same active site but the latter two contain two zinc ions instead of copper ions.
Role of terrestrial carbon in aquatic UV exposure and photoprotective pigmentation of meiofauna in subarctic lakes
2015
Summary Aquatic organisms are adversely influenced by ultraviolet radiation (UV) and utilise photoprotective strategies, including pigmentation. We examined UV-protective melanin pigmentation of aquatic meiofauna (Cladocera) in relation to the UV exposure across 25 tree line lakes in Finland to address the potential effects of increased UV and altered input of UV-screening terrestrial dissolved organic carbon (DOC) on aquatic organisms. Bio-optical parameters, including concentration of DOC, the coloured dissolved organic matter (CDOM) fraction, a suite of carbon quality indices and chlorophyll a, were analysed from lake water, and their role in controlling underwater UV environment (measur…
Comparative transcriptomics of albino and warningly coloured caterpillars
2018
AbstractColouration is perhaps one of the most prominent adaptations for survival and reproduction of most taxa. Colouration is of particular importance for aposematic species, which rely on their colouring and patterning to act as a warning signal against predators. Most research has focused on the evolution of warning colouration by natural selection. However, little information is available for colour mutants of aposematic species, particularly at the genomic level. Here I compare the transcriptomes of albino mutant caterpillars of the wood tiger moth (Arctia plantaginis) to those of their full-sibs having their distinctive orange-black warning colouration. The results showed >300 dif…
Biosynthesis of fungal melanins and their importance for human pathogenic fungi
2003
For more than 40 years fungi have been known to produce pigments known as melanins. Predominantly these have been dihydroxyphenylalanine (DOPA)-melanin and dihydroxynaphthalene (DHN)-melanin. The biochemical and genetical analysis of the biosynthesis pathways have led to the identification of the genes and corresponding enzymes of the pathways. Only recently have both these types of melanin been linked to virulence in some human pathogenic and phytopathogenic fungi. The absence of melanin in human pathogenic and phytopathogenic fungi often leads to a decrease in virulence. In phytopathogenic fungi such as Magnaporthe grisea and Colletotrichum lagenarium, besides other possible functions in …
Polyphenol Oxidases from Wine Grapes
2017
Wine is produced from grapes which contain enzymes forming unfavorable dark polymers such as melanin, oxidizing proteins, and phenols which may influence their functions. Here we focus on the class of type-3 copper proteins presenting new insights on the structure, the occurrence during the ripening process and during wine making. Then, the reactivity of the enzymes on polyphenols from wine grapes are discussed and the possible consequences on health.