FIG. 4.
Interaction between the E. Cloacae 908R β-lactamase and Lek 156. (A) Saturation phenomenon at high concentrations of the compound. The line is drawn from the fit of the data to equation 5 by using the following parameters: k2 equal to 0.37 s−1 and K′ equal to 16 μM (αK′ is equal to 86 μM). Note that above 50 μM, the ki values (>0.135 s−1) become very high so that the mixing dead time constitutes more that 50% of the complete time course, which explains the large errors. (B) The same data described for panel A but with low Lek 156 concentrations ([C]<<αK′), from which a k2/K′ value of 17,500 M−1 s−1 can be calculated. (C) Competitive inhibition between Lek 156 and the reporter substrate (100 μM nitrocefin) after establishment of the steady state, from which a Km value of 0.02 μM is derived by linear regression of the data according to equation 6.