Biol. Pharm. Bull. 28(9) 1566—1570 (2005)

All amino acids except glycine have stereoisomers (Land D-forms). Earlier studies indicate that only L-amino acids are present in higher organisms, such as mammals. However, owing to progress in analytical methods, numerous researchers have recently demonstrated the existence of various naturally occurring D-amino acids in mammals, such as Dserine and D-aspartate (D-Asp). Free D-Asp is present in a wide variety of tissues and cells, particularly the central nervous system and endocrine tissues. The levels of D-Asp change in a variety of organs during development, suggesting that the amino acid plays a significant role in the regulation of developmental processes. In the present review, we discuss our findings together with recent advances in studies on free D-Asp and metabolic systems in mammals.