Metabolic control analysis of the penicillin biosynthetic pathway: the influence of the LLD-ACV : bisACV ratio on the flux control

An extended kinetic model for the first two steps of the penicillin biosynt hetic pathway in Penicillium chrysogenum is set up. It includes the formati on and reduction of the dimer bis-delta-(L-alpha-aminoadipyl)-L-cysteinyl-D -valine (bisACV) from the first pathway intermediate LLD-ACV and their para llel inhibition of the enzyme ACV synthetase (ACVS). The kinetic model is b ased on Michaelis-Menten type kinetics, with non-competitive inhibition of the ACVS by both LLD-ACV and bisACV, and competitive inhibition of the isop enicillin N synthetase (IPNS) by glutathione. The inhibition constant of LL D-ACV, K-ACV is determined to be 0.54 mm. With the kinetic model metabolic control analysis is performed to identify the distribution of rate-control in the pathway at all ratios of LLD-ACV:bisACV. It is concluded that the fl ux control totally resides at the IPNS. This is a result of the regulation of the ACVS by both the LLD-ACV and bisACV demanding a higher flux through the IPNS enzyme to alleviate their inhibition. The measurement of an intrac ellular ratio of LLD-ACV:bisACV to be in the range of 1-2 moles per moles e mphasises the importance of a fast conversion of LLD-ACV to IPN, and accumu lation of LLD-ACV above the K-m-value of the IPNS should therefore be avoid ed.