Penicillin pathway in P. chrysogenum. L-cysteine (Cys), L-valine (Val) and α-amino adipic acid (AAA) are produced from ethanol in central metabolism. These three precursor amino acids are converted into L-α-(δ-aminoadipyl)-L-α-cystenyl-D-α-valine (ACV) by the enzyme L-α-(δ-aminoadipyl)-L-α-cystenyl-D-α-valine synthetase (ACVS, which is coded for by the gene pcbAB). ACV is subsequently converted to isopenicillin-N (IPN) by the enzyme isopenicillin-N synthase (IPNS, which is coded for by the gene pcbC). IPN is then transported into the peroxisome where it is converted into PenG with the precursor PAA, which is added to the medium and imported in the cell and then activated by phenylacetyl CoA ligase to PAA-CoA which is used by the enzyme acyl coenzyme A: Isopenicillin N acyltransferase (AT, which is coded for by the gene penDE). The product PenG is then transported out of the peroxisome and out of the cell into the cultivation medium.