The contribution of alpha-helices to the surface activities of proteins.

The amphilicity of an alpha-helical segment in a protein may be quantitated by calculating its mean helical hydrophobic moment (mu H). For proteins whose hydrophobic interactions with interfaces are mediated by alpha-helices, the surface pressures exerted at the air-water interface correlate with the product (mu H X F) where mu H is the mean helical hydrophobic moment averaged over all helices in the entire molecule, and F is the fraction of alpha-helix in the protein. Knowledge of mu H permits a description of the contribution of amphipathic alpha-helices to the surface activities at the air-water interface of serum apolipoproteins, surface-seeking peptides, and globular water-soluble proteins.