5-S-Cysteinyldopa, a diffusible product of melanocyte activity, is an efficient inhibitor of hydroxylation/oxidation reactions induced by the Fenton system


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Interest in 5-S-cysteinyldopa (5-S-CD), a major excretion product of normal and malignant melanocytes, has traditionally concentrated on its significance as a biosynthetic precursor of pheomelanins, the characteristic pigments of red hair, and as a specific biochemical marker for monitoring melanoma progression. The present study shows that 5-S-CD is a potent inhibitor of hydroxylation/oxidation reactions mediated by hydrogen peroxide and the Fe2+/EDTA complex under both aerobic and anaerobic conditions. The inhibitory effect of 5-S-CD, as determined by the deoxyribose and salicylic acid assays in phosphate buffer (pH 7.4), is much stronger than that of dopa, acctylsalicylic acid and mannitol, increases with increasing ligand-to-metal ratio, and is inversely proportional to the concentration of EDTA present in the Fenton system. Spectrophotometric evidence and competition experiments indicate that 5-S-CD forms a chelate complex with ferric ions (mux = 500 nra at pH 7.4), which may account for both an altered production of hydroxyl radicals by the Fenton reagent and a site-specific localization of oxidative damage on the chelate complex itself.
机译:对5-S-半胱氨酰多巴(5-S-CD)(正常和恶性黑素细胞的主要排泄产物)的兴趣传统上一直集中在其作为色甘素的生物合成前体,红发特征性色素以及特定生化物质的意义上。监测黑色素瘤进展的标志物。本研究表明5-S-CD是有氧和厌氧条件下由过氧化氢和Fe2 + / EDTA复合物介导的羟化/氧化反应的有效抑制剂。通过磷酸盐缓冲液(pH 7.4)中的脱氧核糖和水杨酸测定法确定的5-S-CD抑制作用远强于多巴,乙酰基水杨酸和甘露醇,并随着配体与金属比的增加而增加,并且与Fenton系统中存在的EDTA浓度成反比。分光光度的证据和竞争实验表明,5-S-CD与三价铁离子形成螯合物(在pH 7.4时,mux = 500 nra),这既可以解释芬顿试剂对羟基自由基产生的影响,也可以解释为特定位点螯合复合物本身上氧化损伤的定位。


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