Replacement of tyrosine-197 and the corresponding tyrosine-195 to isoleucine in Cephalosporium acremonium and Streptomyces clavuligerus isopenicillin N synthase.

Isopenicillin N synthase (IPNS) is one of the key enzymes in the penicillin and cephalosporin biosynthetic pathway which catalyses the conversion of delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine to isopenicillin N. The IPNS from Penicillium chrysogenum 23X-80-269-37-2, a high penicillin V-producer, was found to possess an isoleucine residue instead of tyrosine at position 195. An attempt to increase the specific activity of IPNS from Cephalosporium acremonium and Streptomyces clavuligerus was undertaken by altering the corresponding tyrosine residue to an isoleucine at the corresponding location. Unfortunately, no apparent increase in specific activity was encountered when the purified mutant enzymes were analysed and thus, this amino acid difference is likely not responsible for high specific activity in IPNS.