D-aspartate oxidation by rat and bovine renal peroxisomes: an electron microscopic cytochemical study

D-amino acid oxidase, a peroxisomal enzyme, and D-aspartate oxidase, a potential peroxisomal enzyme, share biochemical attributes. Both produce hydrogen peroxide in flavin-requiring oxidative reactions. Such similarities suggest that D-aspartate oxidase may also be localized to peroxisomes. Definitive identification of D-aspartate oxidase as a peroxisomal enzyme depends, however, on visualization at the electron microscopic level. Using incubation conditions shown to be specific for the enzyme in biochemical studies, this report extends the cytochemical localization of D-amino acid oxidase to bovine renal peroxisomes, and shows that D-aspartate can be oxidized by rat and bovine renal peroxisomes. An unexpected finding was the sensitivity of both D-amino acid oxidase activity (proline specific) and D-aspartate oxidase activity to inhibition by agents used in biochemical studies to discriminate between the two enzyme activities. Therefore, it is possible that, in the cytochemical system used in this study, (a) either D-proline and D-aspartate are substrates for only one enzyme or (b) the two enzymes have additional overlapping biochemical properties.