FIGURE 1.

Thermodynamic cycle for peptide binding to the membrane interface and insertion into the bilayer. The folding equilibrium in water lies toward the unstructured state and is determined by $\mathrm{\Delta }{G}_f^o$, which is typically small in comparison with the other terms. The Gibbs energy of binding to the interface ( $\mathrm{\Delta }{G}_{if}^o$) includes contributions from the hydrophobic effect and secondary structure formation. Transfer, as an α-helix, from water to the bilayer interior is approximated by transfer to octanol ( $\mathrm{\Delta }{G}_{\mathit{oct}}^o$). The Gibbs energy of transfer from the surface to the interior of the bilayer is approximately $\mathrm{\Delta }{G}_{\mathit{oct}}^o-\mathrm{\Delta }{G}_{if}^o=\mathrm{\Delta }{G}_{\mathit{oct}-if}^o$. Modified with permission from ref (8). Copyright 2007 Elsevier.