Helical amphipathic moment: application to plasma lipoproteins

The association of apolipoproteins with surfaces occurs with the development of an α-helix in which polar and non-polar faces are formed. The helix locates at the lipid-water interface with the polar face directed toward the aqueous phase and the non-polar face penetrating into the lipid phase. The energetics of this arrangement have been quantified by vector addition of the free energies of transfer of amino acids from water to hydrocarbon to give a resultant helical amphipathic moment. It is shown that the mean residue helical amphipathic moments of the apolipoproteins are consistently higher than those of membrane spanning proteins.