Mosca L, Blarzino C, Coccia R, Foppoli C, Rosei M A
Department of Biochemical Sciences, University of Rome La Sapienza, Roma, Italy.
Free Radic Biol Med. 1998 Jan 1;24(1):161-7. doi: 10.1016/s0891-5849(97)00211-6.
Tetrahydroisoquinolines (TIQs) are endogenous compounds deriving from the nonenzymatic Pictet-Spengler condensation of catecholamines (CA) with aldehydes. TIQs have been extensively studied in the last years not only because they have been found in the brain of postmortem specimens of Parkinson's patients, but also because they are able to induce parkinsonian symptoms if injected in animals. In the present article we demonstrate that TIQs bearing a catecholic moiety (tetrahydropapaveroline, salsolinol, laudanosoline, and apomorphine) are easily oxidized in the presence of hydrogen peroxide by various enzymes--i.e., peroxidase (POD), lipoxygenase (LOX), and xanthine oxidase (XO)--into the corresponding TIQ-melanins. The kinetic parameters of the above-mentioned reactions and some spectroscopic characteristics of the synthetized pigments are reported. In particular, UV-VIS and EPR spectra emerge as very similar to those exhibited by dopa-melanin. Furthermore, TIQ-melanins appear to be similar to dopa-melanin regarding some specific physico-chemical properties: NADH-oxidizing properties, oxy-radicals scavenging activity, and ability to form soluble mixed polymers with melanins from opioid peptides.
四氢异喹啉（TIQs）是内源性化合物，由儿茶酚胺（CA）与醛通过非酶促的Pictet-Spengler缩合反应生成。近年来，TIQs受到了广泛研究，这不仅是因为在帕金森病患者的尸检标本大脑中发现了它们，还因为将其注射到动物体内时能够诱发帕金森症状。在本文中，我们证明了带有儿茶酚部分的TIQs（四氢罂粟碱、萨索林醇、劳丹索林和阿扑吗啡）在过氧化氢存在下很容易被各种酶——即过氧化物酶（POD）、脂氧合酶（LOX）和黄嘌呤氧化酶（XO）——氧化为相应的TIQ-黑色素。本文报道了上述反应的动力学参数以及合成色素的一些光谱特征。特别是，紫外-可见光谱和电子顺磁共振光谱与多巴黑色素所呈现的光谱非常相似。此外，TIQ-黑色素在一些特定的物理化学性质方面似乎与多巴黑色素相似：NADH氧化性质、氧自由基清除活性以及与阿片肽黑色素形成可溶性混合聚合物的能力。
