Kinetics and mechanism of acyl transfer by penicillin acylases.

The hypothesis that at least some penicillin acylases react via an acyl-enzyme intermediate was tested by kinetic investigations involving the methyl ester of cyanoacetic acid as the acyl donor, deacetyl-7-aminocephalosporanic acid as the acyl receptor, and penicillin acylase (E.C.3.5.1.11) from B. megaterium ATCC 14945 as the catalyst. The results obtained at low concentrations of the acyl receptor are in accord with the derived rate equations. Deviations observed at higher concentrations of the acyl receptor are discussed together with some practical implications of the mechanism.