Department of Material and Life Science, Graduate School of Engineering, Osaka University, SORST, Japan Science and Technology Agency (JST), Suita, Osaka 565-0871, Japan.
J Phys Chem B. 2010 Jan 14;114(1):675-80. doi: 10.1021/jp909314t.
Neurotransmitters such as catecholamines (dopamine, L-dopa, epinephrine, norepinephrine) have phenol structure and scavenge reactive oxygen species (ROS) by hydrogen atom transfer (HAT) to ROS. Radical scavenging reactivity of neurotransmitters with galvinoxyl radical (GO*) and cumyloxyl radical (RO*) in acetonitrile at 298 K was determined by the UV-vis spectral change. The UV-vis spectral change for HAT from catecholamine neurotransmitters to GO* was measured by a photodiode array spectrophotometer, whereas HAT to much more reactive cumylperoxyl radical, which was produced by photoirradiation of dicumyl peroxide, was measured by laser flash photolysis. The second-order rate constants (k(GO)) were determined from the slopes of linear plots of the pseudo-first-order rate constants vs concentrations of neurotransmitters. The k(GO) value of hydrogen transfer from dopamine to GO* was determined to be 23 M(-1) s(-1), which is the largest among examined catecholamine neurotransmitters. This value is comparable to the value of a well-known antioxidant: (+)-catechine (27 M(-1) s(-1)). The k(GO) value of hydrogen transfer from dopamine to GO* increased in the presence of Mg(2+) with increasing concentration of Mg(2+). Such enhancement of the radical scavenging reactivity may result from the metal ion-promoted electron transfer from dopamine to the galvinoxyl radical. Inhibition of DNA cleavage with neurotransmitters was also examined using agarose gel electrophoresis of an aqueous solution containing pBR322 DNA, NADH, and catecholamine neurotransmitters under photoirradiation. DNA cleavage was significantly inhibited by the presence of catecholamine neurotransmitters that can scavenge hydroperoxyl radicals produced under photoirradiation of an aerated aqueous solution of NADH. The inhibition effect of dopamine on DNA cleavage was enhanced by the presence of Mg(2+) because of the enhancement of the radical scavenging reactivity.
神经递质，如儿茶酚胺（多巴胺、L-多巴、肾上腺素、去甲肾上腺素）具有酚结构，通过氢原子转移（HAT）清除活性氧（ROS）。在 298 K 下，用乙腈中的半醌自由基（GO*）和枯基自由基（RO*）测定了神经递质的自由基清除反应性。用光电二极管阵列分光光度计测定了儿茶酚胺神经递质与 GO的 HAT 从儿茶酚胺神经递质到 GO的 UV-vis 光谱变化通过激光闪光光解测定了 HAT 到更具反应性的枯基过氧自由基，该自由基是通过过氧化二枯基的光照射产生的。从伪一级速率常数与神经递质浓度的线性图的斜率确定了二级速率常数（k（GO））。从多巴胺到 GO的氢转移的 k（GO）值确定为 23 M-1 s-1，这是所检查的儿茶酚胺神经递质中最大的。该值与一种著名的抗氧化剂：（+）-儿茶素（27 M-1 s-1）相当。在存在 Mg2+的情况下，从多巴胺到 GO的氢转移的 k（GO）值随着 Mg2+浓度的增加而增加。这种自由基清除反应性的增强可能是由于金属离子促进了从多巴胺到半醌自由基的电子转移。还通过含有 pBR322 DNA、NADH 和儿茶酚胺神经递质的水溶液在光照射下的琼脂糖凝胶电泳研究了神经递质对 DNA 断裂的抑制作用。在有氧 NADH 水溶液的光照射下产生的过氧自由基可以被儿茶酚胺神经递质清除，因此 DNA 断裂明显受到儿茶酚胺神经递质的抑制。由于自由基清除反应性的增强，Mg2+的存在增强了多巴胺对 DNA 断裂的抑制作用。
