Napolitano A, Palumbo A, Misuraca G, Prota G
Department of Organic and Biological Chemistry, University of Naples, Italy.
Biochim Biophys Acta. 1993 Jun 12;1168(2):175-80. doi: 10.1016/0005-2760(93)90122-p.
A possible role of melanin precursors in lipid peroxidation was investigated using the lipoxygenase catalysed oxygenation of arachidonic acid (AA) as a model system. Polarographical monitoring of oxygen consumption showed that, among the metabolites examined, 5,6-dihydroxyindole (DHI) was the most active in inhibiting AA oxygenation catalysed by 15-lipoxygenase. The inhibition was found to be concentration-dependent with an IC50 value of 15 microM. Similar effects were observed in the case of the 5-lipoxygenase promoted reaction. Periodical HPLC analysis of the oxidation mixture showed that, in the presence of DHI, the rate of substrate consumption is markedly reduced. The inhibitory potency was significantly increased either by preincubation of DHI with the enzyme or by increasing the time of residence of the indole in aerated buffer solutions prior to contact with the enzyme. Addition of catalase to the incubation mixture resulted in a partial removal of DHI inhibition. From these and other experiments, an inhibition mechanism is proposed which involves inactivation of the enzyme by reactive species, especially hydrogen peroxide, arising from DHI autoxidation.
利用脂氧合酶催化花生四烯酸（AA）的氧化作为模型系统，研究了黑色素前体在脂质过氧化中的可能作用。极谱法监测氧气消耗表明，在所检测的代谢产物中，5,6 - 二羟基吲哚（DHI）对抑制15 - 脂氧合酶催化的AA氧化最为有效。发现这种抑制作用呈浓度依赖性，IC50值为15微摩尔。在5 - 脂氧合酶促进的反应中也观察到类似的效果。对氧化混合物进行定期的高效液相色谱分析表明，在DHI存在的情况下，底物消耗速率明显降低。通过将DHI与酶预孵育，或者通过增加吲哚在与酶接触之前在曝气缓冲溶液中的停留时间，抑制效力显著提高。向孵育混合物中添加过氧化氢酶导致DHI抑制作用部分消除。从这些以及其他实验中，提出了一种抑制机制，该机制涉及由DHI自氧化产生的活性物质，特别是过氧化氢，使酶失活。
