D-aspartate is present in human retinoblastoma Y79 cells

Exocytosis of D-Aspartate from INS-1E Clonal .BETA. Cells

D-Aspartate is present in the central nervous system and various endocrine organs, and modulates their neuroendocrine function. In islets of Langerhans, alpha and beta cells contain D-aspartate. Here we show that INS-1E clonal beta cells contain the highest amount of D-aspartate. Immunohistochemical analysis with specific antibodies against D-aspartate indicated that D-aspartate is co-localized with insulin. Upon the addition of K(+), both D-aspartate and insulin are secreted from the cells in a Ca(2+)-dependent manner. A Ca(2+) ionophore, A23187, also triggers the release of D-aspartate and insulin in the presence of Ca(2+). Bafilomycin A(1), a specific inhibitor of V-ATPase and V-ATPase-linked secondary transport, inhibits the secretion of D-aspartate. These results support the idea that D-aspartate is present in insulin-containing secretory granules and co-secreted with insulin through exocytosis.

Immunohistochemical Localization of D-Aspartate in Islets of Langerhans

D-aspartate is a putative modulator of neuroendocrine functions, and is present in various neuroendocrine cells as well as the central nervous system. Here we show that the islet of Langerhans is a D-aspartate-containing endocrine organ. Immunohistochemical analysis with specific antibodies against D-aspartate indicated that D-aspartate is present in all islet cells, and predominantly present in alpha cells and a subpopulation of F-cells. Since these cells are glutamatergic in nature, it is possible that D-aspartate is involved in the glutamate signaling pathways in the islets.

Cellular and subcellular distribution of D-aspartate oxidase in human and rat brain

The unusual amino acid D-aspartate is present in significant amounts in brain and endocrine glands and is supposed to be involved in neurotransmission and neurosecretion (Wolosker et al. [2000] Neuroscience 100:183-189). D-aspartate oxidase is the only enzyme known to metabolize D-aspartate and could regulate its level in different regions of the brain. We examined the cellular and subcellular distribution of this enzyme and its mRNA in human and rat brain by immunohistochemistry, in situ hybridization, and immunoelectron microscopy. D-aspartate oxidase protein and mRNA are ubiquitous. The protein shows a granular pattern, particularly within neurons and to a significantly lesser extent in astrocytes and oligodendrocytes. No evidence for a synaptic association was observed. Whereas between most positive neurons only gradual differences were observed, in the hypothalamic paraventricular nucleus, neurons with high enzyme content were found next to others with no labeling. cDNA cloning of D-aspartate oxidase corroborates an inherent targeting signal sequence for protein import into peroxisomes. Immunoelectron microscopy showed that the protein is localized in single membrane-bound organelles, apparently peroxisomes.