Enzyme Reaction Engineering: Effect of Methanol on the Synthesis of Antibiotics Catalyzed by Immobilized Penicillin G Acylase under Isothermal and Non-Isothermal Conditions

The effect of methanol on the kinetically controlled synthesis of cephalexin by free and immobilized penicillin G acilase (PGA) was investigared. Catalytic and hydrophobic membranes were obtained by chemical grafting, activation and PGA immobilization on hydrophobic nylon supports. Butyl methacrylate (BMA) was used as graft monomer. Increasing concentrations of methanol were found to cause a greater deleterious effect on the activity of free than on that of the immobilized enzyme. Methanol, however, improved the kinetic stability of cephalexin synthetized by free PGA, resulting in higer maximum yelds. By contrast, immobilized PGA reached 100% yields even in the absence of the cosolvent. Cephalexin sythesis by the catalytic membrane was also performed in a non-isothermal bioreactor. Under these conditions, a 94% increase of synthetic activity and complete conversion of the limiting substrate to the cephalexin were obtained. The addition of methanol reduced the non-isothermal activity increase. The physical cause responsable for the non-isothermal behavior of the hydrophobic catalytic membrane was identified in the process of thermodialysis.