Figure 6.

Time- and concentration-dependent inactivation of human liver microsomal testosterone 6β-hydroxylase activity by verapamil (a). Concentrations of verapamil present in the preincubation samples were 0 µm (NADPH only) (×), 0.5 µm (□), 1 µm (○), 2 µm (Δ) and 5 µm (K). Initial inactivation rate (k) constants were determined at each inhibitor concentration. The reciprocal of k was plotted against the reciprocal of the inhibitor concentration (I) to obtain initial estimates of k_inact and K_I. The inactivation parameters were calculated using a nonlinear regression analysis. A plot of inactivation rate constant vs increasing verapamil concentration is shown (b).