Dunford R, Land E J, Rozanowska M, Sarna T, Truscott T G
Department of Chemistry, Keele University, Staffordshire, UK.
Free Radic Biol Med. 1995 Dec;19(6):735-40. doi: 10.1016/0891-5849(95)00059-7.
The interaction of dopa-melanin (DM) and cysteinyldopa-melanin (CDM) with carbon- and oxygen-centered radicals generated by benzophenone-photosensitized hydrogen abstraction from ethanol, or by pulse radiolysis of aqueous solutions of methanol and ethanol, is reported. Photosensitized formation of carbon-centered radicals and their interaction with melanin was monitored by electron paramagnetic resonance (EPR) spin trapping using DMPO, and via the melanin free radical signal itself. In the pulse radiolysis experiments, the interaction of DM or CDM with hydroxymethyl, hydroxyethyl, and the corresponding methanol peroxyl radical was monitored by recording time-dependent changes of the melanin absorbance at selected wavelengths. The data indicate that both melanins are good scavengers of carbon-centered radicals, with corresponding rate constants in the range of 10(7) to 10(8) M-1 s-1. Significantly, compared to DM, CDM is also an exceptionally efficient scavenger of oxygen-centered radicals derived from methanol with corresponding rate constants of 2.7 x 10(4) and 2 x 10(6) M-1 s-1 for DM and CDM, respectively. The results are discussed with reference to the potential role of melanin in protecting the integrity of melanosomes by inhibiting peroxidation of lipid components of the organelle membrane.
报道了多巴黑素（DM）和半胱氨酰多巴黑素（CDM）与由二苯甲酮光敏引发的乙醇氢提取产生的碳中心自由基和氧中心自由基的相互作用，或者与甲醇和乙醇水溶液脉冲辐解产生的自由基的相互作用。通过使用DMPO的电子顺磁共振（EPR）自旋捕获以及通过黑素自由基信号本身监测碳中心自由基的光敏形成及其与黑素的相互作用。在脉冲辐解实验中，通过记录选定波长下黑素吸光度的时间依赖性变化，监测DM或CDM与羟甲基、羟乙基以及相应的甲醇过氧自由基的相互作用。数据表明，两种黑素都是碳中心自由基的良好清除剂，相应的速率常数在10(7)至10(8) M-1 s-1范围内。值得注意的是，与DM相比，CDM也是甲醇衍生的氧中心自由基的异常高效清除剂，DM和CDM的相应速率常数分别为2.7 x 10(4)和2 x 10(6) M-1 s-1。结合黑素通过抑制细胞器膜脂质成分的过氧化作用来保护黑素体完整性的潜在作用对结果进行了讨论。
