[The Free Form of D-Amino Acids As a Novel Bioactive Substance: Physiological Functions and Involvement in Human Pathophysiology].

It was long considered that.D-amino acids were either unnatural isomers or laboratorial artifacts, and that the important functions of amino acids were exerted only by L-amino acids. However, recent investigations have shown that a variety of D-amino acids are present in various organisms, including mammals, and that they play important roles in physiological functions in the body. Here, we present an overview of recent studies of free D-amino acids, focusing on the expression and localization in tissues and cells, biological and physiological activities, biosynthesis, cellular transport, and degradation. From the point of view of human pathophysiology, the possible relevance of free D-amino acids to disease is also described. [Review].