Ferrous active site of isopenicillin N synthase: genetic and sequence analysis of the endogenous ligands

Genetic and sequence analysis indicates that the His212, His268, and Asp214 endogenous ligands form the ferrous active site of isopenicillin N synthase (IPNS) from Streptomyces jumonjinensis. Mutations in these residues remove enzymatic activity. The fourth ligand is a glutamine residue that is probably replaced when the substrate binds to the enzyme. Enzymatic activity is unaffected by site directed mutagenesis of the other histidine residues and aspartic acid residues which are conserved in bacterial and fungal IPNS. These substitutions produce no observable conformational changes.