Time- and concentration-dependent inactivation of CYP 2B1 S360A. CYP 2B1 S360A was reconstituted with reductase and incubated with different concentrations of 17EE in the absence or presence of NADPH as described in Experimental Procedures. Aliquots were removed at 0, 2, 4, 8, and 16 min and assayed for residual 7-EFC activity. (□), 0 μM; (■) 1 μM; (△) 2 μM; (▲) 4 μM; (○) 8 μM and (●) 16 μM 17EE. The inset shows the double reciprocal plot of the inverse of the rates of inactivation vs the inverse of the substrate concentration which was used to estimate the kinetic constants describing the inactivation reaction.