Summary: Isopenicillin N (IPN) epimerase, an enzyme involved in cephalosporin and cephamycin biosynthesis that converts IPN into penicillin N, was extracted from and purified 88-fold. The enzyme was unstable but could be partially stabilized by addition of pyridoxal phosphate. The purified enzyme did not require ATP for activity in contrast to other amino acid racemases. The enzyme had an of 59000 as determined by gel filtration; IPN epimerase from had an of 63000. A protein band of 59000 was found to be enriched in SDS-PAGE of active fractions from The optimal temperature of the epimerase was 25°C and the optimal pH 7.0. The apparent for IPN was 270 μM. Fe, Cu, Hg and Zn strongly inhibited enzyme activity. α-Aminoadipic acid, valine, glutamine, glycine, aspartic acid and glutathione do not affect enzyme activity, whereas ammonium sulphate was inhibitory. The epimerase activity was partially inhibited by several thiol-specific reagents.


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