D-Amino acid

ᴅ-Amino acids are amino acids where the stereogenic carbon alpha to the amino group has the ᴅ-configuration. For most naturally-occurring amino acids, this carbon has the ʟ-configuration. ᴅ-Amino acids are occasionally found in nature as residues in proteins. They are formed from ribosomally-derived ᴅ-amino acid residues.

Amino acids, as components of peptides, peptide hormones, structural and immune proteins, are the most important bioregulators involved in all life processes along with nucleic acids, carbohydrates and lipids. "Environmental ᴅ-amino acids are thought to be derived from organic diagenesis such as racemization and release from bacterial cell walls and even from microbial production."