The Physiological Role of D-Amino Acid Oxidase in the Mammalian Central Nervous System

为了阐明含有黄素的过氧化物酶--D-氨基酸氧化酶(DAO)在哺乳动物中枢神经系统中的生理作用，有必要探讨DAO的组织学定位及其与半胱胺和乙醛的加合物--噻唑烷-2-羧酸盐(TC)氧化活性的关系。该方法基于镍离子对过氧化物酶催化生成二氨基联苯胺基产物的强化作用。DAO活性仅定位于下部脑干、小脑和脊髓，仅存在于星形胶质细胞和Bergmann胶质细胞，而不存在于神经元成分、内皮细胞和室管膜细胞。从电子显微镜观察，DAO活性在各种突触周围的神经胶质间隙中所占比例较大。我们还将上述技术应用于TC氧化酶活性的检测。该酶在大鼠肾、肝、脑中的定位与DAO一致。另一方面，另一种过氧化体黄素酶D-天冬氨酸氧化酶的活性在终脑中没有检测到DAO活性，这一结果清楚地表明了星形胶质细胞的区域分化和过氧化物体酶在脑内的不均匀分布。DAO可能通过控制半胱胺及其代谢物草酰硫醇酯的细胞内水平参与代谢调节，这是已知的代谢效应。

To elucidate the physiological role of D-amino acid oxidase (DAO), a flavin-containing peroxisomal enzyme, in the mammalian central nervous system, it isimportant to explore the histological localization of DAO and its correlation to the oxidizing activity of thiazolidine-2-carboxylate (TC), which is an adduct of cysteamine and glyoxylate and is believed to be a physiological substrate for DAO.Using serial fixed sections, we carried out a histochemical study on DAO in the whole brain of rat by a sensitive peroxidase-coupled procedure which we devised for histochemical detection of DAO activity. This method is based on the intensifying effect of nickel ions on diaminobenzidinebased product formation with peroxidase. DAO activity was found to be localized exclusively in the lower brain stem, cerebellum and spinal cord, and to be present only in astrocytes and Bergmann glial cells, but not in neuronal components, endothelial cells or ependymal cells. Form electron microscopic observations, the greater proportion of DAO activity was present in the glial spaces around various kinds of synapses. We also applied the above technique for the detection of TC oxidase activity. The localizations of this oxidase activity in the kidney, liver and brain of rat were in accord with those of DAO. On the other hand, the activity of D-aspartate oxidase, another peroxisomal flavoenzyme, was found in the endbrain in which DAO activity was not detectable.The above results clearly demonstrate the regional differentiation of astrocytes and the uneven distribution of peroxisomal enzymes in the brain. It is also suggested the possibility that DAO is involved in the metabolic regulation by controlling the intracellular level of cysteamine and its metabolite, an oxalyl thiol ester, which are known to be metabolic effectors.