Cuevas A A, García-Castiñeiras S
Department of Ophthalmology, School of Medicine, Univeristy of Puerto Rico, San Juan 00936-5067.
P R Health Sci J. 1993 Jun;12(2):129-35.
Based on previous findings that lens pigments and melanins share many physicochemical properties, human lens pigments and natural (hair) and synthetic melanins were submitted to oxidation with permanganate under strong acidic conditions. This procedure has been utilized for the characterization of melanins and results in the well defined products, thiazole-4,5-dicarboxylic acid (TDCA) and pyrrole-2,3,5-tricarboxylic acid (PTCA), which can be quantitated by high performance liquid chromatography (HPLC). PTCA is regarded as a marker of black eumelanins and was therefore a main component of synthetic DOPA-eumelanin and dark hair. Its identity was established by synthesis from 5-hydroxyindole-2-carboxylic acid. TDCA derives from pheomelanins and was therefore an important component of red hair and synthetic GSH-pheomelanin. TDCA was identified by its retention time relative to PTCA. The analysis of a series of cataract digests of increasing pigmentation (type I < type IV < type V) and a purified fraction of lens pigments (DE52 pigment) revealed the presence in these preparations of both PTCA and TDCA. The concentration of TDCA significantly increased with the degree of pigmentation of the digests and reached a maximum in the DE52 pigment. The TDCA/PTCA ratio was high in the lens preparations and comparable to that given by hair pheomelanin. These findings support that pheomelanin is an integral part of lens pigments. By comparing the yields of TDCA in GSH-pheomelanin and in the purified lens pigment, a 9% contribution of pheomelanin to the lens pigment was estimated.
基于之前的研究发现，晶状体色素和黑色素具有许多物理化学性质，因此将人晶状体色素、天然（毛发）黑色素和合成黑色素在强酸性条件下用高锰酸盐进行氧化处理。该方法已用于黑色素的表征，并产生了定义明确的产物噻唑 - 4,5 - 二羧酸（TDCA）和吡咯 - 2,3,5 - 三羧酸（PTCA），它们可通过高效液相色谱（HPLC）进行定量分析。PTCA被视为黑色真黑色素的标志物，因此是合成多巴真黑色素和深色毛发的主要成分。通过由5 - 羟基吲哚 - 2 - 羧酸合成确定了其结构。TDCA源自褐黑素，因此是红发和合成谷胱甘肽 - 褐黑素的重要成分。通过与PTCA的保留时间对比鉴定出了TDCA。对一系列色素沉着程度增加的白内障消化物（I型<IV型<V型）以及晶状体色素的纯化级分（DE52色素）进行分析，结果显示这些制剂中同时存在PTCA和TDCA。TDCA的浓度随着消化物色素沉着程度的增加而显著升高，并在DE52色素中达到最大值。晶状体制剂中的TDCA/PTCA比值较高，与毛发褐黑素的比值相当。这些发现支持褐黑素是晶状体色素的一个组成部分。通过比较谷胱甘肽 - 褐黑素和纯化的晶状体色素中TDCA的产量，估计褐黑素对晶状体色素的贡献为9%。
