High level expression in Escherichia coli of isopenicillin N synthase genes from Flavobacterium and Streptomyces, and recovery of active enzyme from inclusion bodies.

A T7 promoter-based vector was used to express the isopenicillin N synthase (IPNS) genes of Flavobacterium sp. 12,154 and Streptomyces jumonjinensis in Escherichia coli. Most of the IPNS synthesized at 37 degrees C, and representing some 22% and 51% of the total cell protein respectively, occurred in an insoluble, enzymatically inactive form. Active IPNS was recovered in a rapid and simple two-step procedure in which the insoluble material was first denatured in 5 M urea and then refolded by passing the solubilized IPNS through a G-25 Sephadex sizing column. Further chromatography on DEAE-Sepharose resulted in highly active IPNS preparations. This procedure was found to be well suited for scaling up to produce large amounts of IPNS.