D-Aspartate oxidase and free acidic d-amino acids in lower vertebrates

Abstract

d-Aspartate oxidase and free d-aspartate and/or d-glutamate have been found in various tissues of lower vertebrates including avians, amphibians and fishes. The enzymes of those animals were similar to the mammalian enzymes in substrate and inhibitor specificity. N-Methyl- d-aspartate is the best substrate of the enzymes of those animals, followed by d-aspartate, meso-2,3-diaminosuccinate and d-glutamate. In avians and amphibians, the highest activity was found in the kidneys, whereas, in fishes, hepatic activity was equal to or greater than renal activity. Male chickens had significantly higher activities in the liver, kidneys and pancreas than female. However, no significant sex difference was observed in other animals. Substantial amounts of d-aspartate and/or d-glutamate were detected in all tissues examined, irrespective of species. With the exception of the spleen or testes of some species, the d-glutamate content was equal to or greater than the d-aspartate content. The amounts of d-enantiomer present were significantly different between two sexes in several tissues of avians and amphibians. However, no common relationship was observed between the d-enantiomer contents and d-aspartate oxidase activity. The involvement of d-aspartate in the control of androgen secretion by the ovary was demonstrated in a green frog.