Immunocytochemical localization of D-amino acid oxidase in rat brain

D-amino acid oxidase (D-AAO) is a peroxisomal flavoenzyme, the physiological substrate and the precise function of which are still unclear. We have investigated D-AAO distribution in rat brain, by immunocytochemistry, with an affinity-purified polyclonal antibody. Immunoreactivity occurred in both neuronal and glial cells, albeit at different densities. Glial immunostaning was strongest in the caudal brainstem and cerebellar cortex, particularly in astrocytes, Golgi-Bergmann glia, and tanycytes. Hindbrain neurons were generally more immunoreactive than those in the forebrain. Immunopositive forebrain cell populations included mitral cells in the olfactory bulb, cortical and hippocampal neurons, ventral pallidum, and septal, reticular thalamic, and paraventricular hypothalamic nuclei. Within the positive regions, not all the neuronal populations were equally immunoreactive; for example, in the thalamus, only the reticular and anterodorsal nuclei showed intense labelling. In the hindbrain, immunopositivity was virtually ubiquitous, and was especially strong in the reticular formation, pontine, ventral and dorsal cochlear, vestibular, cranial motor nuclei, deep cerebellar nuclei, and the cerebellar cortex, especially in Golgi and Purkinje cells.

Presence of D-amino-acid oxidase protein in mutant mice lacking D-amino-acid oxidase activity

1. Mutant mice lacking D-amino-acid oxidase activity were examined as to whether they possessed the enzyme protein. 2. Immunoblotting using an antibody against hog kidney D-amino-acid oxidase showed that kidney homogenates of the mutant mice as well as that of the normal mice had proteins reactive to the antibody. 3. Peroxisomal proteins of the kidney cells of the mutant mice were not different from those of the normal mice. 4. The peroxisomes of the mutant mice possessed a protein reactive to the antibody in the immunoblotting whose size was the same as the D-amino-acid oxidase protein present in the peroxisomes of the normal mice. 5. These results suggest that the mutant mice synthesize the D-amino-acid oxidase protein and integrate it into peroxisomes, though it is a nonfunctional enzyme.

Immunochemical relationship of D-amino acid oxidases in various tissues and animals

1. By means of an enzyme immunoassay, the contents of D-amino acid oxidase (DAO) were determined in kidney, liver, cerebellum and lung of hog, but the oxidase was not detectable in heart or cerebrum. 2. The oxidases in kidney, liver and cerebellum of hog were indistinguishable as regards immunoreactivity toward anti-hog kidney DAO antibody, specific activity and molecular weight. 3. The oxidases in rat and dog kidneys immunochemically cross-reacted with anti-hog DAO antibody. 4. The overall structure of the hog oxidase was more similar to that of the dog enzyme than that of the rat, while the structure around the catalytic site of the hog oxidase was more similar to that of the rat oxidase than that of the dog enzyme. 5. On immunoblot analysis, two forms of the oxidase were detected in extracts of hog, rat and dog kidneys.

In vivo and in vitro expression of porcine D-amino acid oxidase: in vitro system for the synthesis of a functional enzyme

In vivo expression of D-amino acid oxidase (EC 1.4.3.3, DAO), one of the principal and characteristic enzymes of the peroxisomes of porcine kidney, was examined by use of cloned complementary DNA [Fukui, K., Watanabe, F., Shibata, T., & Miyake, Y. (1987) Biochemistry 26, 3612-3618]. RNA blot hybridization analysis revealed that DAO is expressed abundantly in kidney and liver, is expressed significantly in brain, but is not expressed in lung of pig. Three mRNA species were expressed in kidney and liver, but only one was detected in brain. These results show the presence of tissue-specific regulation of DAO gene expression. In vitro expression of a functional enzyme was achieved through the construction of a recombinant plasmid containing an SP6 promoter and a restriction enzyme fragment of cDNA to generate a DAO-specific RNA transcript. The in vitro translation product of the capped RNA transcript showed significant catalytic activity, which was inhibited strongly by benzoate, a potent inhibitor of DAO. The kinetic properties of the in vitro synthesized enzyme were comparable to those of the purified enzyme from porcine kidney. It is now possible to synthesize a functional D-amino acid oxidase in vitro and to investigate its structure-function relationships.

Immunochemical properties of D-amino-acid oxidase

Antiserum against homogeneous hog kidney D-amino-acid oxidase (D-amino-acid: oxygen oxidoreductase (deaminating), EC 1.4.3.3) was elicited in rabbits, and monospecific antibodies were prepared by affinity chromatography. The antibodies inhibited up to 90% of hog D-amino-acid oxidase activity, and 100% of the enzyme could be immunoprecipitated. The antibodies inhibited both holoenzyme and reconstituted apoprotein to a similar degree, indicating that they did not interfere with the FAD-binding site of the protein. The antibodies inhibited D-amino-acid oxidase activity from other mammalian species to a similar degree, while the enzyme activities from birds, amphibians, fishes and yeast were inhibited and immunoprecipitated to lower extents. In immunoblotting experiments, after SDS-polyacrylamide gel electrophoresis, the antibodies recognized a single band of about 40 kDa in all the species analyzed, and the entity of the signal was inversely related to the phylogenetic distance from mammals. The antibodies did not inhibit D-alanine dehydrogenase activity from Escherichia coli, but gave positive bands in immunoblotting.