Helix-coil transition in the case of interaction between two chains

Based on the generalized model of polypeptide chain the helix-coil transition in two chains, which are interacting abreast, is studied. There are four types of interaction (hh, hc, ch, cc). The Hamiltonian of system includes the basic Hamiltonian for two chains and the term which is responsible for interactions. It is shown that, when the energy of one type interaction (hh, cc) is more than the energy of mixed-type interaction (hc, ch), the correlation length grows sharply and melting interval becomes narrower. The system has a nontrivial behavior when the energy of mixed-type interactions (hc, ch) is higher than that of the one-type interaction (hh, cc). In this case one can observe the growth of the correlation length, and the melting curve has a two-stage character. The portion of junctions and the average length of helical fractions show that the merging and breakup of helical fractions take place.