Abstract The influence of the substrate structure on the catalytic properties of penicillin G acylase (PGA) from Escherichia coli in kinetically controlled acylations has been studied. In particular, the affinity of different β-lactam nuclei towards the active site has been evaluated considering the ratio between the rate of synthesis (vs) and the rate of hydrolysis of the acylating ester (v h1). 7-Aminocephalosporanic acid (7-ACA) and 7-amino-3-(1- ...