δ-(l-α-Aminoadipyl)-l-cysteinyl-d-valine synthetase, that mediates the first committed step in penicillin biosynthesis, is a cytosolic enzyme

Abstract

Penicillin biosynthesis by Penicillium chrysogenum is a compartmentalized process. The first catalytic step is mediated by delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase (ACV synthetase), a high molecular mass enzyme that condenses the amino acids L-alpha-aminoadipate, L-cysteine, and L-valine into the tripeptide ACV. ACV synthetase has previously been localized to the vacuole where it is thought to utilize amino acids from the vacuolar pools. We localized ACV synthetase by subcellular fractionation and immuno-electron microscopy under conditions that prevented proteolysis and found it to co-localize with isopenicillin N synthetase in the cytosol, while acyltransferase localizes in microbodies. These data imply that the key enzymatic steps in penicillin biosynthesis are confined to only two compartments, i.e., the cytosol and microbody.

Peroxisomes Are Required for Efficient Penicillin Biosynthesis in Penicillium chrysogenum

“…1). The first two enzymes, ACVS and IPNS, are both located in the cytosol (19,32). As the pH of the cytosol in filamentous fungi is between 6.5 and 7.0 (9, 31), these enzymes are in their optimal physiological surroundings.…”

Penicillins

“…However, the biochemical properties of this enzyme, such as in vitro optimal pH 8.4 (which resulted to be above that of the vacuolar pH), cofactor requirement, and protease sensitivity indicated that this enzyme was a cytosolic enzyme. This fact was confi rmed by immunoelectron microscopy [ 39 ].…”

Cephalosporins

“…Figure 3.2 shows the chromosomal organization of both genes, which share a bidirectional promoter and are intron-free, suggesting that they were passed from prokaryotes to eukaryotes by horizontal gene transfer [ 19 ]. The corresponding gene products have a cytoplasmic localization, indicating that the fi rst two biosynthesis steps occur in the cytoplasm [ 20 ].…”