Inhibition kinetics of three R-factor-mediated beta-lactamases by a new beta-lactam sulfone (CP 45899).

A new beta-lactam sulfone, CP 45899, has been proved to be a time-dependent irreversible inhibitor of three R-factor-mediated beta-lactamases (penicillin amido-beta-lactamhydrolase, EC 3.5.2.6): TEM-1 (pI = 5.4), TEM-2 (pI = 5.6) and Pitton's type 2 (pI = 7.7). This inhibition occurs in two principal steps: (1) formation of a reversible enzyme-inhibitor complex (characterized by a Ki); (2) evolution of this complex into one, or more, inactive protein(s) (kinact). With the three beta-lactamases CP 45899 shows, respectively, Ki of 0.9, 0.8 and 1.8 microM and kinact of 1.2 . 10(-3), 0.8 . 10(-3) and 1 . 10(-3) s-1; the turnover numbers are: 525, 2280 and 1220. These results are compared to those previously obtained with clavulanic acid.