Roberts J E, Hu D N, Wishart J F
Fordham University, New York, NY 10023, USA.
J Photochem Photobiol B. 1998 Feb;42(2):125-32. doi: 10.1016/s1011-1344(97)00132-2.
The endogenous indole melatonin and the melatonin receptor agonist 6-chloromelatonin block the proliferation of both dermal and uveal melanoma cells by mechanisms that may involve redox reactions. The interactions of hydrated electrons, the azide radical, hydroxyl radicals and superoxide with melatonin and its 6-chloro analogue have been studied using the technique of pulse radiolysis. The reaction rate constants of eaq- and N3 x with these compounds were found to be dependent on substitution at the sixth position. The rate constants for reaction of 6-chloromelatonin and melatonin with solvated electrons are 4.5 x 10(9) M-1 s-1 and 4.2 x 10(8) M-1 s-1, respectively. The reaction rate constants of N3 x with malatonin and chloromelatonin are 9.8 x 10(9) M-1 s-1 and 3.5 x 10(9) M-1 s-1 and 3.5 x 10(9) M-1 s-1, respectively. Melatonin and 6-chloromelatonin react with hydroxyl radicals at near diffusion controlled rates (1.3 x 10(10) M-1 s-1, 8.2 x 10(9) M-1 s-1). Melatonin and 6-chloromelatonin did not react with superoxide radicals and we calculate an upper limit of 1.0 x 10(4) M-1 s-1 for the rate constant for reaction of melatonin and 6-chloromelatonin with superoxide ion.
内源性吲哚褪黑素和褪黑素受体激动剂6-氯褪黑素通过可能涉及氧化还原反应的机制，阻断皮肤黑素瘤细胞和葡萄膜黑素瘤细胞的增殖。利用脉冲辐解技术研究了水合电子、叠氮自由基、羟基自由基和超氧阴离子与褪黑素及其6-氯类似物的相互作用。发现水合电子和叠氮自由基与这些化合物的反应速率常数取决于第六位的取代情况。6-氯褪黑素和褪黑素与溶剂化电子反应的速率常数分别为4.5×10⁹ M⁻¹ s⁻¹和4.2×10⁸ M⁻¹ s⁻¹。叠氮自由基与褪黑素和氯褪黑素的反应速率常数分别为9.8×10⁹ M⁻¹ s⁻¹和3.5×10⁹ M⁻¹ s⁻¹。褪黑素和6-氯褪黑素以接近扩散控制的速率（1.3×10¹⁰ M⁻¹ s⁻¹，8.2×10⁹ M⁻¹ s⁻¹）与羟基自由基反应。褪黑素和6-氯褪黑素不与超氧阴离子反应，我们计算出褪黑素和6-氯褪黑素与超氧离子反应速率常数的上限为1.0×10⁴ M⁻¹ s⁻¹。
