Presence of free D-glutamate and D-aspartate in rat tissues.

The presence of free D-glutamate was demonstrated for the first time in rat liver, kidney and brain. This is based on the findings that the D-glutamate as well as D-aspartate in the tissue extracts co-chromatographed exactly with the authentic standards on HPLC, and that the treatment of the extracts with D-aspartate oxidase mostly abolished the HPLC peaks of these compounds. Contents of these acidic D-amino acids in the liver and kidney, as well as the percentages of D/(D + L), were lower in female than in male, while D-aspartate oxidase activities in the same tissues were inversely lower in male than in female, in agreement with a probable role of the enzyme. A significant correlation was observed between D-aspartate and D-glutamate contents in the liver, kidney and brain of individual animals, with the D-glutamate contents always higher than the D-aspartate contents.