Figure 2.

Schematic representation of the mechanism of penicillin action. PGN is composed of polysaccharide chains made of GlcNAc and MurNAc units (shown in different shades of blue) which in turn have small peptides attached to them. The transpeptidase enzyme (PBP) (in brown) catalyzes the formation of cross-linkages between these peptides, by specifically binding the last two D-alanine residues of one peptide (red circles). Penicillin mimics the structure of these residues and inactivates the PBP by forming an irreversible covalent bond to the catalytic serine residue of the enzyme [69].