METABOLIC CONTROL ANALYSIS OF THE PENICILLIN BIOSYNTHETIC-PATHWAY IN A HIGH-YIELDING STRAIN OF PENICILLIUM-CHRYSOGENUM

Metabolic control analysis is used to identify the rate-limiting step in the penicillin biosynthetic pathway in Penicillium chrysogenum. The analysis is carried out using a kinetic model for the first two steps in the pathway, i.e., the ACV synthetase (ACVS) and the isopenicillin N synthetase (IPNS). The kinetic model is based on Michaelis-Menten t ype kinetics, with noncompetitive inhibition of the ACVS by ACV and co mpetitive inhibition of the IPNS by glutathione. From measurements of the enzyme activities and intracellular metabolites during a fed-batch cultivation, the kinetic model is used to predict the flux through th e pathway. The model prediction corresponds well with the measured rat e of penicillin biosynthesis. From measurement of the activity of the acyl-CoA:isopenicillin acyltransferase, which catalyzes the third and last reaction in the pathway, it is concluded that the rate-limiting s tep is either at the ACVS or at the IPNS. From the kinetic model, the elasticity coefficients and the flux control coefficients are calculat ed throughout the fed-batch cultivations, and it is found that there i s a shift in the flux control from the ACVS to the IPNS during the cul tivation.