The alpha-helix as an electric macro-dipole.

A polypeptide chain is found to form an electric macro-dipole in solution when it is folded to take the alpha-helical conformation. This is due to the polar peptide residues, all of which are oriented to have their moment in the axial direction in its regular helical conformation. This remarkable electric nature of the alpha-helix has extensively been examined for nearly twenty years, and the study is still in a state of development. The dielectric behavior of a solution consisting of the macrodipole is one major concern of the study, and the other is to probe with this unique property into the regular conformation and helix-coil transition of polypeptides. Historical and topical, but not comprehensive, surveys have been given here for both of these dielectric aspects of the alpha-helix.