D-alanine transpeptidase (specifically, D- alanyl- D-alanine carboxypeptidase, and DD transpeptidase ) is an enzyme found only in bacteria. It is therefore responsible for the crosslinking of the carbohydrate components ( peptidoglycan ) of the bacterial cell walls, and their strength. The enzyme is the starting point for beta -lactam antibiotics (eg, penicillin) that inhibit its enzymatic activity irreversible; In this case, the antibiotic will form a stable bond with the active center amino acids, and thus prevents de novo synthesis of the cell wall, whereby the cell division is stopped ( bacteriostatic effect).

The DD- transpeptidase is a penicillin- binding protein. There are several families of enzymes with similar activity, belonging both to the serine proteases and the other to the metalloproteases. There are four families of enzymes distinguished that have different origins: D -alanyl- D-alanine carboxypeptidase A, B and C, and zinc -D -Ala- D -Ala- carboxypeptidases.

Catalyzed reaction

The cross-linking of the cell wall takes place between peptide moieties, which are connected to N- acetylmuramic acid carbohydrate with the proportion of the peptidoglycans. These are in particular D-alanine residues. She mainly plays a role in cell division, since parts of the cell wall must be re- synthesized.