Helix-helix transitions in polypeptides

A statistical mechanical. treatment concerning the helix-helix transition of polypeptide chains was attempted based on a model which specifies the state of each peptide residue by either right-handed screw sense or left-handed screw sense. Two principal parameters were introduced. gamma is the statistical weight of a right-handed helical residue that follows one or more other right-handed helical residues rho represents the difficulty for the initiation of a right-handed sequence after a run of left-handed segments. To account for the newly discovered multiple helix-helix transitions,the acid effect was further incorporated into the theory. The proposed theory was compared with experimental results and some published data,and the agreement is encouraging.