{Reference Type}: Review {Title}: Biosynthesis and Degradation of Free D-Amino Acids and Their Physiological Roles in the Periphery and Endocrine Glands. {Author}: Katane M;Homma H; {Journal}: Biol Pharm Bull {Volume}: 47 {Issue}: 3 {Year}: 2024 {Factor}: 2.264 {DOI}: 10.1248/bpb.b23-00485 {Abstract}: It was long believed that D-amino acids were either unnatural isomers or laboratory artifacts, and that the important functions of amino acids were exerted only by L-amino acids. However, recent investigations have revealed a variety of D-amino acids in mammals that play important roles in physiological functions, including free D-serine and D-aspartate that are crucial in the central nervous system. The functions of several D-amino acids in the periphery and endocrine glands are also receiving increasing attention. Here, we present an overview of recent advances in elucidating the physiological roles of D-amino acids, especially in the periphery and endocrine glands.