Fig. 3.

(A) Inactivation of coumarin hydroxylase activity as a function of t-CA concentration, preincubation period, and NADPH in a recombinant CYP2A6 system (●, buffer; ▪, NADPH; ▴, 10 µM t-CA; ▾, 20 µM t-CA; ♦, 40 µM t-CA; ○, 80 µM t-CA; □, 120 µM t-CA). Data points are the mean of three individual experiments conducted on separate days (N = 3 for each point). The percentage of control activity was determined by comparing the activity to the average activity of samples with CYP2A6 that did not contain NADPH or t-CA. (B) Determination of k_inact and K_I by fitting k_obs (min⁻¹) to eq. 1.