Schematic representation of the penicillin G (PenG) biosynthetic pathway in <i>P. chrysogenum</i>.

<p>In the cytosol, the enzyme ACVS (ACVS-OH) is activated by a PPTase into ACVS-SH. The active enzyme produces ACV from the three precursor molecules AAA, L-cysteine and L-valine. IPNS subsequently converts ACV into the β-lactam IPN, which is transported into peroxisomes. In this organelle PAA is activated by PCL into phenylacetyl CoA (PA-CoA), which is used by IAT to synthesize PenG from IPN. PenG is exported from the organelle and ultimately secreted into the medium. The precursors and intermediates of PenG biosynthesis pathway are boxed.