D-Amino acid aminotransferase (D-aAt) catalyses the transamination of various D-amino acids, forming their respective keto acids. The enzyme has no sequence similarity to the well studied L-amino acid aminotransferase but does have significant sequence overlap with a bacterial branched-chain L-amino acid aminotransferase and 4-amino-4-deoxychorismate lyase. D-aAt is essential for the synthesis of bacterial cell wall components and has been a target of research in the development of antimicrobial agents.

Acts on the D-isomers of alanine, leucine, aspartate, glutamate, aminobutyrate, norvaline and asparagine. The enzyme transfers an amino group from a substrate D-amino acid to the pyridoxal phosphate cofactor to form pyridoxamine and an alpha-keto acid in the first half-reaction. The second-half reaction is the reverse of the first, transferring the amino group from the pyridoxamine to a second alpha-keto acid to form the product D-amino acid via a ping-pong mechanism. This is an important process in the formation of D-alanine and D-glutamate, which are essential bacterial cell wall components.