Studies on the biosynthesis of isopenicillin N with a cell-free preparation of Penicillium chrysogenum.

Abstract

When .delta.-(L-.alpha.-aminoadipyl)-L-cysteinyl-D-valine was added to a cell-free system prepared by lysis of P. chrysogenum protoplasts, compounds X and Y were detected after analysis on a cation-exchange column. The chromatographic position and results of experiments with double labeled tripeptides showed compound X to be the penicilloic acid of isopenicillin N. LLD-Tripeptide labeled with tritium at carbon-2 of the valine part was incorporated into isopenicillin N with retention of label. Compound Y retained all hydrogens on the valine part of the peptide but lost half of the tritium on carbon-3 of the cysteine part. This is consistent with the hypothesis that the LLD-tripeptide is converted into isopenicillin N via a monocyclic .beta.-lactam and without a dehydrovalinyl intermediate. Extensive transacylase activity was observed between isopenicillin N and 6-aminopenicillanic acid.