Fig. 1

The antimicrobial action of β-lactamase against the peptidoglycan structure of the bacterial cell membrane. Peptidoglycan possesses a basic structural unit in which two amino sugars of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) alternate, and a longitudinal peptide chain linked to NAM forms a pillar. This peptide chain is a pentapeptide consisted of alternating d- and l-forms of l-alanine, γ-d-glutamic acid, l-lysine, d-alanine, and d-alanine that forms a bacterial enzyme known as penicillin-binding protein (PBP). PBP recognizes alanyl-alanine, which is an alanine dimer formed by d-alanine-d-alanine present at the end of the pentapeptide, and exerts the enzymatic action of cross-linking. Since penicillin is structurally similar to alanyl-alanine at the terminal region of the pillar structure, PBP captures penicillin, thereby inhibiting the cross-linking reaction