In enzymology, a D-alanine—D-alanine ligase (EC 6.3.2.4) is an enzyme that catalyzes the chemical reaction

ATP + 2 D-alanine ${\displaystyle \rightleftharpoons }$ ADP + phosphate + D-alanyl-D-alanine

Thus, the two substrates of this enzyme are ATP and D-alanine, whereas its 3 products are ADP, phosphate, and D-alanyl-D-alanine.

This enzyme belongs to the family of ligases, specifically those forming carbon-nitrogen bonds as acid-D-amino-acid ligases (peptide synthases). The systematic name of this enzyme class is D-alanine:D-alanine ligase (ADP-forming). Other names in common use include alanine:alanine ligase (ADP-forming), and alanylalanine synthetase. This enzyme participates in d-alanine metabolism and peptidoglycan biosynthesis. Phosphinate and D-cycloserine are known to inhibit this enzyme.

The N-terminal region of the D-alanine—D-alanine ligase is thought to be involved in substrate binding, while the C-terminus is thought to be a catalytic domain.^[1]

As of late 2007, 8 structures have been solved for this class of enzymes, with PDB accession codes 1EHI, 1IOV, 1IOW, 2DLN, 2FB9, 2I80, 2I87, and 2I8C.