Inhibition of cell wall synthesis Penicillin and most other β-lactam<unk>  act by inhibiting penicillin-binding proteins, which normally catalyze cross-linking of bacterial cell walls. β-lactam<unk>  are bactericidal, and act by inhibiting the synthesis of the peptidoglycan layer of bacterial cell walls. The peptidoglycan layer is important for cell wall structural integrity, especially in Gram-positive organisms, being the outermost and primary component of the wall. The final transpeptidation step in the synthesis of the peptidoglycan is facilitated by DD-transpeptidases, also known as penicillin binding proteins (PBPs). PBPs vary in their affinity for penicillin and other β-lactam<unk> . The number of PBPs varies between bacterial species. β-lactam<unk>  are analogues of -alanyl--alanine—the terminal amino acid residues on the precursor NAM/NAG-peptide subunits of the nascent peptidoglycan layer. The structural similarity between β-lactam<unk>  and -alanyl--alanine facilitates their binding to the active site of PBPs. The β-lactam nucleus of the molecule irreversibly binds to (acylates) the Ser403 residue of the PBP active site. This irreversible inhibition of the PBPs prevents the final crosslinking (transpeptidation) of the nascent peptidoglycan layer, disrupting cell wall synthesis. β-lactam<unk>  block not only the division of bacteria, including cyanobacteria, but also the division of cyanelles, the photosynthetic organelles of the glaucophytes, and the division of chloroplasts of bryophytes. In contrast, they have no effect on the plastids of the highly developed vascular plants. This is supporting the endosymbiotic theory and indicates an evolution of plastid division in land plants. Under normal circumstances, peptidoglycan precursors signal a reorganisation of the bacterial cell wall and, as a consequence, trigger the activation of autolytic cell wall hydrolases. Inhibition of cross-linkage by β-lactams causes a build-up of peptidoglycan precursors, which triggers the digestion of existing peptidoglycan by autolytic hydrolases without the production of new peptidoglycan. As a result, the bactericidal action of β-lactam<unk>  is further enhanced. Guanine oxidation Another possibility that has been proposed to account for much of the cytotoxicity of<unk><unk> s focuses on the oxidation of the guanine nucleotide in the bacterial nucleotide pool. The incorporation of oxidized guanine nucleotide into DNA could cause cytotoxicity. Bacterial cytotoxicity could arise from incomplete repair of closely spaced 8-oxo-2'-deoxyguanosine lesions in the DNA resulting in double-strand breaks.
Beta-lactam antibiotics
Quinolone antibiotic
Steroid
Antiarthritics
Broad-spectrum antibiotic
Antibiotic
Lipase inhibitors
Polypeptide antibiotic