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Interference of Some Tryptophan Metabolites in the Formation of Melanin In Vitro

机译:黑色素形成过程中某些色氨酸代谢产物的干扰

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Melanin (eumelanin) is commonly produced in mammals starting from tyrosine and/or 3,4-dioxyphenylalanine (DOPA) under the action of tyrosinase. 3-Hydroxyanthranilic acid and 3-hydroxykynurenine are intermediates occurring in the kynurenine pathway of tryptophan catabolism. In this paper, we show that these substances can interfere in melanin formation in vitro when tyrosine or DOPA is oxidized by molecular oxygen under catalysis by tyrosinase. In particular, when 3-hydroxyanthranilic acid is present, a brown and apparently water-soluble pigment is formed, whereas the typical eumelanin granules seem to become more and more rare as the concentration of 3-hydroxyanthranilic acid increases. Also in the presence of the latter, the rate of tyrosine and/or DOPA consumption decreases. A very complicated ~(13)C-NMR spectrum indicates the high complexity of the reaction. This involves both the true melanin precursor(s) and the tryptophan metabolite, even if with peculiar mechanism and kinetics. When 3-hydroxykynurenine is substituted for 3-hydroxyanthranilic acid the reaction leads to reddish pigments whereas xanthommatins (the typical oxidation products of 3-hydroxykynurenine) are absent. A possible relationship between some dischromic pathologies and tryptophan metabolic disorders is suggested.
机译:黑色素(木聚糖)通常在酪氨酸酶的作用下从酪氨酸和/或3,4-二氧苯基丙氨酸(DOPA)开始在哺乳动物中产生。 3-羟基邻氨基苯甲酸和3-羟基犬尿氨酸是色氨酸分解代谢的犬尿氨酸途径中的中间体。在本文中,我们表明当酪氨酸酶或酪氨酸酶催化酪氨酸或DOPA被分子氧氧化时,这些物质可在体外干扰黑色素的形成。特别地,当存在3-羟基邻氨基苯甲酸时,形成棕色且显然是水溶性的颜料,而典型的丁晴类颗粒随着3-羟基邻氨基苯甲酸浓度的增加而变得越来越稀有。同样在后者的存在下,酪氨酸和/或DOPA消耗的速率降低。非常复杂的〜(13)C-NMR光谱表明反应高度复杂。即使具有独特的机理和动力学,这也涉及真正的黑色素前体和色氨酸代谢产物。当用3-羟基尿嘧啶酸代替3-羟基邻氨基苯甲酸时,该反应导致带红色的颜料,而没有黄嘌呤类固醇(3-羟基尿嘧啶的典型氧化产物)。建议在某些变色病理和色氨酸代谢紊乱之间可能存在关系。

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