The Physiological Role of Flavin-dependent Oxidases in Mammalian Peroxisome

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Adducts of sulfhydryl compounds and glyoxylate are substrates for the flavooxidases in peroxisome. The products can be hydrolyzed to oxalyl thiol ester which is proposed to be a metabolic effector. On the other hand, the activities of certain enzymes and receptors can be modulated by thiol/disulfide exchange reactions. The intracellular thiol/disulfide status appears to play an important role in cellular regulations and responses.Thiazolidine-2-carboxylate (TC), an adduct of cysteamine and glyoxylate, is a substrate for D-amino acid oxidase (DAO). The histochemical localizations of TC oxidase activity in various tissues of rat were in accord with those of DAO. Both oxidase activities were histochemically and biochemically shown to be due to the same enzyme, DAO. The activity of DAO was 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 other types of glial cells, neurons, endothelial cells or ependymal cells. The greater proportion of DAO activity was present in the glial spaces around various kinds of synapses, whereas D-aspartate oxidase activity was found in the endbrain in which DAO activity was not detectable, suggesting that the distribution of the two oxidases is supplementary in brain. On the other hand, the direct actions of sulfhydryl compounds such as cysteamine to vascular smooth muscle and membrane-bound phospholipase A_2 were also investigated. From these results, the possibility is suggested that peroxisomal flavooxidases are involved in the cellular regulations by participating in metabolisms of sulfhydryl compounds and biosynthesis of oxalyl thiol ester.