Koch W H, Chedekel M R
Biochim Biophys Acta. 1987 Jun 22;924(3):458-66. doi: 10.1016/0304-4165(87)90161-9.
We have recently demonstrated that cysteinyldopas, pheomelanogenic precursors and excreted eumelanogenic metabolites, are photolabile and initiate DNA damage in vitro. In this study we have extended our photochemical investigations to eumelanogenic indole intermediates and metabolites. Continuous-wave photolysis of 5,6-dihydroxyindole (DHI), 5,6-dihydroxyindole-2-carboxylic acid (DHICA), or its 5-methoxylated metabolite (HMICA) with biologically relevant ultraviolet radiation (i.e., wavelengths greater than 300 nm) resulted in rapid destruction of starting material. Using ESR spin-trapping techniques we observed the initial production of free radical species; prolonged photolysis resulted in the formation of polymeric photoproducts. Radicals were trapped by the nitrone spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and characterized by their ESR spectra as hydrated electrons and hydrogen atoms. Experiments further demonstrated that while DHI photoionizes, the two indole-2-carboxylic acid derivatives do not ionize appreciably upon irradiation, rather homolysis of X-H bonds appears to be a significant photochemical pathway. The potential photobiological significance of melanogenic indole intermediates is discussed.
我们最近证明，半胱氨酰多巴、褐黑素生成前体和排出的真黑素生成代谢物具有光不稳定特性，并在体外引发DNA损伤。在本研究中，我们将光化学研究扩展到真黑素生成的吲哚中间体和代谢物。用具有生物学相关性的紫外线（即波长大于300nm）对5,6-二羟基吲哚（DHI）、5,6-二羟基吲哚-2-羧酸（DHICA）或其5-甲氧基化代谢物（HMICA）进行连续波光解，导致起始原料迅速分解。使用电子自旋共振（ESR）自旋捕获技术，我们观察到自由基种类的初始产生；长时间光解导致聚合物光产物的形成。自由基被硝酮自旋捕获剂5,5-二甲基-1-吡咯啉N-氧化物（DMPO）捕获，并通过其ESR光谱表征为水合电子和氢原子。实验进一步证明，虽然DHI发生光电离，但两种吲哚-2-羧酸衍生物在辐照时不会明显电离，相反，X-H键的均裂似乎是一条重要的光化学途径。本文讨论了黑素生成吲哚中间体潜在的光生物学意义。
