The isopenicillin‐N acyltransferase of Penicillium chrysogenum has isopenicillin‐N amidohydrolase, 6‐aminopenicillanic acid acyltransferase and penicillin amidase activities, all of which are encoded by the single penDE gene

Abstract

The isopenicillin‐N acyltransferase of Penicillium chrysogenum catalyzes the conversion of the biosynthetic intermediate isopenicillin N to the hydrophobic penicillins. The isopenicillin‐N acyltransferase copurified with the acyl‐CoA:6‐aminopenicillanic acid (6‐APA) acyltransferase activity which transfers an acyl residue from acyl‐CoA derivatives (e.g. phenylacetyl‐CoA, phenoxyacetyl‐CoA) to 6‐APA. Other thioesters of phenylacetic acid were also used as substrates. An amino acid sequence similar to that of the active site of thioesterases was found in the isopenicillin‐N acyltransferase, suggesting that this site is involved in the transfer of phenylacetyl residues from phenylacetyl thioesters. Purified isopenicillin‐N acyltransferase also showed isopenicillin‐N amido‐hydrolase, penicillin transacylase and penicillin amidase activities. The isopenillin‐N amidohydrolase (releasing 6‐APA) showed a much lower specific activity than the isopenicillin‐N acyltransferase of the same enzyme preparation, suggesting that in the isopenicillin‐N acyltransferase reaction the 6‐APA is not released and is directly converted into benzylpenicillin. Penicillin transacylase exchanged side chain between two hydrophobic penicillin molecules; or between one penicillin molecule and 6‐APA. The penicillin amidase activity is probably the reverse of the biosynthetic acyl‐CoA:6‐APA acyltransferase. Four P. chrysogenum mutants deficient in acyl‐CoA:6‐APA acyltransferase lacked the other four related activities. Transformation of these mutants with the penDE gene restored all five enzyme activities. Copyright © 1993, Wiley Blackwell. All rights reserved