Kinetic properties of the Bacillus licheniformis penicillin-binding proteins

In the analysis of the interactions between beta-lactam antibiotics and their target enzymes, it is often difficult to estimate the kinetic properties of the molecules which react rapidly with their targets and in consequence behave as the most efficient antibiotics. The combined utilization of fluorescein-labelled penicillins and of a new competition method has allowed an accurate determination of the high second-order rate constants characterizing the acylation of Bacillus licheniformis penicillin-binding protein 1 (PBP1) by penicillins and cephalosporins. Strategies were devised for measuring high acylation rates while avoiding titration effects. The method was also suitable for measuring the PBP kinetic parameters in intact cells. These results also confirmed that PBP1 is probably the main target of most beta-lactam antibiotics. Cephalexin, however, reacted faster with PBP3.