Pilas B, Sarna T, Kalyanaraman B, Swartz H M
Department of Biophysics, Jagiellonian University, Krakow, Poland.
Free Radic Biol Med. 1988;4(5):285-93. doi: 10.1016/0891-5849(88)90049-4.
The effects of melanin on the iron-catalyzed decomposition of hydrogen peroxide to hydroxyl radicals and hydroxyl ions have been studied using electron spin resonance, spin trapping and visible light spectrophotometry. Melanin altered these reactions by several different mechanisms and consequently, depending on conditions, can significantly increase or decrease the yield of reactive products, including hydroxyl radicals. For low concentrations of ferrous ions, melanin decreased the yield of hydroxyl radicals due to binding of ferrous ions by melanin; ferrous ions bound to melanin did not decompose H2O2 efficiently. Melanins increased the rate of hydroxyl radical production if the predominant form of iron was ferric, due to the ability of melanin to reduce ferric to ferrous iron. Hydroxyl radical production in the presence of a strong chelator (e.g. EDTA) and melanin was greater than in the presence of a weak chelator (e.g. ADP) and melanin. Melanin also increased the rate of destruction of the DMPO-OH adduct.
利用电子自旋共振、自旋捕获和可见光分光光度法研究了黑色素对铁催化过氧化氢分解为羟基自由基和氢氧根离子的影响。黑色素通过几种不同机制改变这些反应，因此，根据条件的不同，它可以显著增加或降低包括羟基自由基在内的反应产物的产量。对于低浓度的亚铁离子，由于黑色素与亚铁离子结合，黑色素降低了羟基自由基的产量；与黑色素结合的亚铁离子不能有效地分解过氧化氢。如果铁的主要形式是三价铁，黑色素会提高羟基自由基的产生速率，这是因为黑色素具有将三价铁还原为二价铁的能力。在存在强螯合剂（如乙二胺四乙酸）和黑色素的情况下，羟基自由基的产生量大于存在弱螯合剂（如二磷酸腺苷）和黑色素的情况。黑色素还提高了DMPO-OH加合物的破坏速率。
