In order to characterize the phenotype and to examine the effects of sun exposure on the color and structure of eumelanin (EM) and pheomelanin (PM) in alpaca fibers, we applied Soluene-350 solubilization, alkaline hydrogen peroxide oxidation (AHPO) and hydroiodic acid (HI) hydrolysis to the base and tip fibers of 20 true-black (TB) and 20 warm-black (WB) alpacas. We analyzed absorbances at 500 nm (A500) and 650 nm (A650), Free and Total pyrrole-2,3,5-tricarboxylic acid (PTCA), 2,3,4,5-tetracarboxylic acid (PTeCA) as degradative products from EM, and 4-amino-3-hydroxyphenylalanine (4-AHP), 3-amino-4-hydroxyphenylalanine (3-AHP) and thiazole-2,4,5-tricarboxylic acid (TTCA) as degradative products from PM. We found that the ratio of PTeCA/Total PTCA increased significantly from the base to the tip in both colors of alpaca fibers, while the ratios of A650/A500 and 4-AHP/3-AHP decreased significantly. These results show that structures made of both EM and PM in alpaca fibers are modified significantly by sun exposure inducing color change. This study indicates that the ratios of A650/A500, PTeCA/Total PTCA and 4-AHP/3-AHP are highly sensitive markers of color change and photodegradation of EM and PM, respectively.

中文翻译：

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黑色素的光漂白氧化降解：羊驼纤维中黑色素的化学表征

为了表征表型并检查阳光照射对羊驼纤维中真黑素 (EM) 和褐黑素 (PM) 颜色和结构的影响，我们应用了 Soluene-350 增溶、碱性过氧化氢氧化 (AHPO) 和氢碘酸(HI) 水解为 20 只真黑 (TB) 和 20 只暖黑 (WB) 羊驼的基部和尖端纤维。我们分析了 500 nm (A500) 和 650 nm (A650)、游离和总吡咯-2,3,5-三羧酸 (PTCA)、2,3,4,5-四羧酸 (PTeCA) 作为降解产物的吸光度EM 和 4-氨基-3-羟基苯丙氨酸 (4-AHP)、3-氨基-4-羟基苯丙氨酸 (3-AHP) 和噻唑-2,4,5-三羧酸 (TTCA) 作为 PM 的降解产物。我们发现，在两种颜色的羊驼毛纤维中，PTeCA/Total PTCA 的比例从基部到尖端都显着增加，而A650/A500和4-AHP/3-AHP的比值显着下降。这些结果表明，羊驼纤维中由 EM 和 PM 制成的结构通过阳光照射引起的颜色变化显着改变。该研究表明，A650/A500、PTeCA/Total PTCA 和 4-AHP/3-AHP 的比率分别是 EM 和 PM 颜色变化和光降解的高度敏感标志物。