Zavodnik I B, Domanski A V, Lapshina E A, Bryszewska M, Reiter R J
Department of Membrane Biochemistry, Institute of Biochemistry, National Academy of Sciences of Belarus, Blvd. Leninskogo Komsomola 50, 230017 Grodno, Belarus.
Life Sci. 2006 Jun 20;79(4):391-400. doi: 10.1016/j.lfs.2006.01.030. Epub 2006 May 15.
Melatonin, a pineal secretory product, has properties of both direct and indirect powerful antioxidant. The aim of the present study was to compare the radical-scavenging, structural and electronic properties of melatonin and tryptophan, precursor of melatonin. Using the alkoxyl- and peroxyl radical-generating systems [the organic peroxide-treated human erythrocytes and a cell-free system containing the azo-initiator 2,2'-azobis(2-amidinopropane)dihydrochloride], we evaluated the radical-scavenging effects of melatonin and tryptophan. Melatonin rather than tryptophan at concentrations of 100-2000 microM markedly inhibited membrane lipid peroxidation in human erythrocytes treated with organic hydroperoxide as well as radical-induced generation of luminol-dependent chemiluminescence. The apparent Stern-Volmer constants for inhibition of membrane lipid peroxidation by melatonin and tryptophan were estimated to be (0.23+/-0.05) x 10(4) M(-1) and (0.02+/-0.005) x 10(4) M(-1), respectively. The apparent Stern-Volmer constants for inhibition of azo-initiator-derived peroxyl radical generation by melatonin and tryptophan were determined to be (0.42+/-0.05) x 10(4) M(-1) and (0.04+/-0.01) x 10(4) M(-1), respectively. The structural and electronic properties of melatonin and its precursor, tryptophan, were determined theoretically by performing semi-empirical and ab initio calculations. The high radical-scavenging properties of melatonin may be explained by the high surface area value and high dipole moment value. From the thermodynamic standpoint, based on our calculations, N(1)-acetyl-N(2)-formyl-5-methoxykynuramine (AFMK), was the most stable end oxidative product of melatonin.
褪黑素是松果体分泌的一种产物，具有直接和间接的强大抗氧化特性。本研究的目的是比较褪黑素与其前体色氨酸的自由基清除、结构和电子特性。我们使用烷氧基和过氧自由基生成系统（有机过氧化物处理的人类红细胞以及含有偶氮引发剂2,2'-偶氮二（2-脒基丙烷）二盐酸盐的无细胞系统）评估了褪黑素和色氨酸的自由基清除效果。在100 - 2000微摩尔浓度下，褪黑素而非色氨酸能显著抑制经有机氢过氧化物处理的人类红细胞中的膜脂质过氧化以及自由基诱导的鲁米诺依赖性化学发光的产生。褪黑素和色氨酸抑制膜脂质过氧化的表观斯特恩 - 沃尔默常数分别估计为(0.23±0.05)×10⁴ M⁻¹和(0.02±0.005)×10⁴ M⁻¹。褪黑素和色氨酸抑制偶氮引发剂衍生的过氧自由基生成的表观斯特恩 - 沃尔默常数分别确定为(0.42±0.05)×10⁴ M⁻¹和(0.04±0.01)×10⁴ M⁻¹。通过进行半经验和从头计算从理论上确定了褪黑素及其前体色氨酸的结构和电子特性。褪黑素的高自由基清除特性可能由其高表面积值和高偶极矩值来解释。从热力学角度来看，基于我们的计算，N(1)-乙酰基-N(2)-甲酰基-5-甲氧基犬尿胺（AFMK）是褪黑素最稳定的最终氧化产物。
