Purification and characterization of Alcaligenes faecalis penicillin G acylase expressed in Bacillus subtilis

The Alcaligenes faecalis PGA gene encoding heterodimeric penicillin G acylase (PGA) was cloned and successfully expressed in Escherichia coli and Bacillus subtilis respectively. In contrast to E. coli hosts where the enzymes were retained in the periplasm, B. subtilis cell secreted the recombinant enzyme into the medium. Contrary to limited expression yield of E coli (pETAPGA), PGA extracellularly expressed by B. subtilis (pBAPGA)and B. subtilis (pMAPGA)reached the highest yield of 653 u/L. This yield increased 109-fold higher than the native expression of A. faecalis CICC AS1.767. The enzyme was fractionated with (NH4)(2)SO4 and purified by DEAE-Sepharose CL-6B with a yield of 81 %. The purified enzyme had a specific activity of 1.469 u/mg. Furthermore, some enzyme characteristics, such as the pH and temperature optimum, the stability against organic solvent and the ratio of cepholexin synthesis to hydrolysis were determined. By overexpressing A. faecalis PGA in B. subtilis and purifying secreted enzyme from culture medium one could readily obtain a large amount of an alternative source of PGA.