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

Isopenicillin N synthase (IPNS) is one of the key enzymes in the penicillin and cephalosporin biosynthetic pathway which catalyses the conversion Of d elta-(L-alpha -aminoadipyl)-L-cysteinyl-D-valine to isopenicillin N. The IP NS from Penicillium chrysogenum 23X-80-269-37-2, a high penicillin V-produc er, was found to possess an isoleucine residue instead of tyrosine at posit ion 195. An attempt to increase the specific activity of IPNS from Cephalos porium acremonium and Streptomyces clavuligerus was undertaken by altering the corresponding tyrosine residue to an isoleucine at the corresponding lo cation. Unfortunately, no apparent increase in specific activity was encoun tered when the purified mutant enzymes were analysed and thus, this amino a cid difference is likely not responsible for high specific activity in IPNS .