A new spectrophotometric assay for dopachrome tautomerase

Aroca, Pilar; Solano, Francisco; García-Borrón, J.C.; Lozano, JoséA.

doi:10.1016/0165-022x(90)90043-c

Cited by 58 publications

(41 citation statements)

References 17 publications

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“…The literature values for the absorption cross sections of DHI and DHICA vary, depending on the solvent, pH, or both; representative values are 1720 (in deaerated water) and 6590 M -1 cm -1 (in NaOH solution), respectively. [40][41][42] Both molecules exhibit larger absorption cross sections in phosphate buffer (4485 and 8205 M -1 cm -1 for DHI and DHICA, respectively). Thus, if the DHI/DHICA ratio were to change for the eumelanin present in the melanosomes from different colored irides, then the data in Table 1 could reflect changes in the eumelanin pigment.…”

Section: Discussionmentioning

confidence: 99%

The Ultraviolet Absorption Coefficient of Melanosomes Decreases with Increasing Pheomelanin Content

Peles

Simon

2010

J. Phys. Chem. B

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Uveal melanosomes from the iridal stroma contain both eumelanin and pheomelanin, the ratio of which varies with iris color. Herein, we report the absorption coefficient at λ ) 244 nm for individual human iridal stroma melanosomes from dark brown and blue-green irides. The melanosomes are nearly identical in size, but differ in the relative concentration composition, ranging from a eumelanin/pheomelanin ratio of 14.8:1 (dark brown) to 1.3:1 (blue-green or hazel). The absorption coefficient of the melanosome decreases as its pheomelanin content increases. The origin of this decrease is attributed to a corresponding decrease in the number of UV-absorbing chromophores, reflecting the different molecular volumes of the monomeric building blocks of the two pigments. In agreement with reported data on synthetic pigments, the absorption coefficient of pheomelanin is found to be slightly larger than that for eumelanin at λ ) 244 nm (by a factor of 1.2). On the basis of the reported optical properties of synthetic models, this result suggests that the absorption of pheomelanin is less than eumelanin at wavelengths of biological relevance (∼315-400 nm).

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Section: Discussionmentioning

confidence: 99%

The Ultraviolet Absorption Coefficient of Melanosomes Decreases with Increasing Pheomelanin Content

Peles

Simon

2010

J. Phys. Chem. B

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“…Some inhibitors have already been identified, e.g., N-(3,5-dimethylphenyl)-3-methoxybenzamide [83] and Neolitsea aciculata extract [84]. Further identification of TRP-2 inhibitors appears to be crucial, and a bioassay consisting of spectrophotometrical monitoring at 308 nm of the absorbance increase due to the TRP-2 controlled tautomerization of DOPAchrome to DHICA as a function of time has been developed [85].…”

Section: Testing the Whitening Potential Of A Given Substancementioning

confidence: 99%

Skin Whitening Cosmetics: Feedback and Challenges in the Development of Natural Skin Lighteners

et al. 2016

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Abstract:With the public's growing interest in skin whitening, lightening ingredients only used under dermatological supervision until recently, are more and more frequently incorporated into cosmetic formulas. The active agents that lighten skin tone are either natural or synthetic substances, and may act at various levels of melanogenesis. They are used to treat various skin pigmentation disorders or simply to obtain a lighter skin tone as whiter skin may be synonymous of wealth, health, youth, and/or beauty in different cultures. However, recent studies demonstrated the adverse effects of some of these ingredients, leading to their interdiction or restricted use under the European Directive and several other international regulations. After an overview of skin whitening practices and the associated risks, this article provides insight into the mechanisms involved in melanin synthesis and the biological assays available to attest the lightening activity of individual ingredients. The legislation dealing with the use of skin lighteners is then discussed. As traditional depigmenting agents such as hydroquinone and corticosteroids are of safety concern, the potential of natural extracts has been investigated more and more; finally, a synthesis of three years of research in our laboratory for such plant extracts will be given.

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“…The assay medium was 0.1 mM L-dopachrome in 10 mM sodium phosphate, pH 6.0, containing 0.1 mM EDTA. L-Dopachrome was chemically prepared, immediately before use, by L-Dopa oxidation with sodium periodate, using a stoichiometry of 1 : 2 [17]. D-Dopachrome and L-dopachrome methyl ester were prepared from D-Dopa and L -D o~ methyl ester in a similar way.…”

Section: Enzyme Activity Determinationsmentioning

confidence: 99%

“…DCT activity was spectrophotometrically determined by monitoring the decrease in absorbance at 475 nm ( E = 3700 M-' cm-') due to L-dopachrome decoloration [lo, 111, or alternatively the increase in absorbance at 308 nm [17] due to the conversion of dopachrome to DHICA. Both reactions were carried out at 30 "C in a thermostatically regulated Varian spectrophotometer.…”

Section: Enzyme Activity Determinationsmentioning

confidence: 99%

Regulation of the final phase of mammalian melanogenesis

Aroca

Solano

Salinas

et al. 1992

European Journal of Biochemistry

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The regulation of the final steps of the melanogenesis pathway, after ~-2-carboxy-2,3-dihydroindole-5,h-quinonc (dopachrome) formation, is studied. It is shown that both tyrosinase and dopachrome tautomerase are involved in the process. In vivo, it seems that tyrosinase is involved in the regulation of the amount of melanin formed, whereas dopachrome tautomerase is mainly involved in the size, structure and composition of melanin, by regulating to the incorporation of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) into the polymer. Moreover, using ~-3,4-dihydroxyphenylalanine (dopa) and related compounds, it was shown that the presence of dopachrome tautomerase mediates an initial acceleration of melanogenesis since L-dopachrome is rapidly transformed to DHICA, but that melanin formation is inhibited because of the stability of this carboxylated indole compared to 5,6-dihydroxyindole (DHI), its decarboxylated counterpart obtained by spontaneous decarboxylation of L-dopachrome. Using L-dopa methyl ester as a precursor of melanogenesis, it is shown that this carboxylated indole does not polymerize in the absence of DHI, even in the presence of tyrosinase. However, it is incorporated into the polymer in the presence of both tyrosinase and DHI. Thus, this study suggests that DHI is essential for melanin formation, and the rate of polymerization depends on the ratio between DHICA and DHI in the medium. In the melanosome, this ratio should be regulated by the ratio between the activities of dopachrome tautomerase and tyrosinase.In mammals, melanin pigmentation results from the biosynthetic and secretory activity of specialized cells called melanocytes. The main biological function of melanin is in protection against ultraviolet radiation [l], but another possible role for this pigment is to act as a scavenger of cytotoxic agents, such as amines, free radicals and metal ions, preventing undesirable cellular processes [2, 31.The early key steps in the melanogenic pathway, the 0-hydroxylation of c-Tyr to ~-3,4-dihydroxyphenylalanine (dopa) and the oxidation of L-Dopa to L-dopaquinone, are catalyzed by tyrosinase [4, 51. Until 1980, it was believed that the reactions subsequent L-dopaquinone in the pathway leading to melanin, the Raper-Mason pathway, were spontaneous and proceeded through a series of unstable intermediates, such as (2-carboxy-2,3-dihydroindole-5,6-quinone) (Ldopachrome), 5,6-dihydroxyindole (DHI) and 5,6-indolequinone (IndQu) [4-61. However. the content of carboxylic Correspondence to F. Solano,

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A new spectrophotometric assay for dopachrome tautomerase

Cited by 58 publications

References 17 publications

The Ultraviolet Absorption Coefficient of Melanosomes Decreases with Increasing Pheomelanin Content

The Ultraviolet Absorption Coefficient of Melanosomes Decreases with Increasing Pheomelanin Content

Skin Whitening Cosmetics: Feedback and Challenges in the Development of Natural Skin Lighteners

Regulation of the final phase of mammalian melanogenesis

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