Activity and stability of immobilized penicillin amidase at low pH values

Penicillin amidase is being applied widely in the production of semi-synthetic β-lactam antibiotics. Usually the processes are at pH 7–8, but for many new applications the range of pH 3–6 is of interest too. Therefore, we studied the activity of penicillin amidase at 25 °C in potassium phosphate buffer of pH 3.7–9, as well as its stability in potassium phosphate buffer of pH 3–6. At each pH, the enzyme was stable during at least 32 days. On the other hand, immobilized penicillin amidase incubated in butyl acetate lost its stability, showing after 32 days a decrease of 52% in relation to its initial enzymatic activity value. In phosphate buffer, the enzyme showed the highest activity at pH 8–9. A gradual decrease to about 20% of this activity occurred when the pH was decreased to 3.7. At even lower pH, the enzyme activity could not be determined with the assay that was used due to a very low stability of penicillin G (PenG). The course of penicillin G conversion and 6-aminopenicillanic acid (APA) production, during enzymatic hydrolysis at pH 4, could be quantitatively described by a simple model when the thermodynamic equilibrium of the hydrolysis was taken into account.