FIGURE 6.

tBid exists in two major conformations at the membrane. The fluorescence lifetime of samples of 20 nm cBid labeled with NBD at different residues with and without 7.2 nm liposomes was measured. The data were analyzed using a model that included a hydrophilic (τ₁) and a hydrophobic lifetime (τ₂) and noise. The fractions corresponding to each lifetime (f₁ and f₂) are shown as open and solid bars, respectively, for the residues indicated below the bars, with (+) and without (−) liposomes (Lipos). The various regions probed are indicated at the bottom as in Fig. 5. The values of lifetimes (ns) are indicated on the bars (mean ± S.E., n = 3–4) and roughly divide the protein into the three regions (N terminus, membrane inserting, and C terminus) as indicated at the top.