Figure 8.

Binding of ketoconazole to cytochome P450 (P450) 3A4. The final P450 3A4 concentration was 2 μM, and the final ketoconazole concentration was 15 μM (in 100 mM potassium phosphate buffer, pH 7.4). A, spectral traces at 390 and 425 nm. B, spectra acquired at the indicated times after mixing, as indicated. The data were collected in the OLIS Show Pre-trigger Mode, with 2.1 s of data from the previous run (completed reaction) shown prior to mixing. C, time course of early ΔA₃₉₀ − A₄₂₅ change in the early phase after mixing. D, traces of ΔA₄₂₅ − A₃₉₀ following the first 18 s after mixing, as a function of ketoconazole concentration. E, plots of k_obs values from biexponential fits of data of part D plotted versus final ketoconazole concentration.