Parameters of ligand interactions with CYP3A4 determined by steady-state and time-resolved LRET*.

*Life-time measurements were performed at nearly-saturating ligand concentrations, which were equal to 100 µM, 2.5 µM, 50 µM and 100 µM for ANF, bromocriptine, cholesterol, and testosterone, respectively. The respective values of LRET efficiency (ΔELT) were calculated according to Eq. 2 using the value of τd (lifetime in the absence of acceptor) equal to 234 µs (see Table S1). In the case of steady state measurements, the change in LRET efficiency (ΔE) were calculated from the maximal relative change in the intensity of donor fluorescence found from the approximation of LRET titration curves with a combination of Eq. 4 and Eq. 5. The values given in the table represent the averages of 3–7 individual measurements, and the ± values show the confidence interval calculated for p = 0.05. The values of the distance changes were considered significant if their confidence interval falls outside the −0.5 - +0.5 Å window. These values are emphasized in bold.aNot determined – in these cases the amplitude of the changes was too small to obtain a reliable estimate of the dissociation constant.