Fig. 3. Enzymes catalysing β-lactam formation during antibiotic biosynthesis, including: (A) isopenicillin N synthase (IPNS), (B) β-lactam synthetase (BLS), (C) CarA, and (D) non-ribosomal peptide synthetases (NRPS) SulN and NocB. Outline mechanisms/steps are shown. Note that not all cofactors, co-substrates, and products are shown. PAPS: 3'-phosphoadenosine-5'-phosphosulfate; PCP: peptidyl-carrier protein.