Penicillin acylase‐catalyzed ampicillin synthesis using a pH gradient: A new approach to optimization

The penicillin acylase‐catalyzed synthesis of ampicillin by acyl transfer from D‐(–)‐phenylglycine amide (D‐PGA) to 6‐aminopenicillanic acid (6‐APA) becomes more effective when a judiciously chosen pH gradient is applied in the course of the process. This reaction concept is based on two experimental observations: 1) The ratio of the initial synthesis and hydrolysis rates (V S /V H ) is pH‐dependent and exhibits a maximum at pH 6.5–7.0 for a saturated solution of 6‐APA; 2) at a fixed 6‐APA concentration below saturation, V S /V H increases with decreasing pH. Optimum synthetic efficiency could, therefore, be achieved by starting with a concentrated 6‐APA solution at pH 7 and gradually decreasing the pH to 6.3 in the course of 6‐APA consumption. A conversion of 96% of 6‐APA and 71% of D‐PGA into ampicillin was accomplished in an optimized procedure, which significantly exceeds the efficiency of enzymatic synthesis performed at a constant pH of either 7.0 or 6.3. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 78: 589–593, 2002.