The helix-coil transition in polypeptides: a microscopic approach. II

In the framework of an earlier constructed model [N.S. Ananikyan et al. (1990) Biopolymers, Vol. 30, pp. 357-367], some analytical estimates for the correlation length and degree of helicity near the transition point were obtained in the case of an arbitrary topology of hydrogen bond closing (delta). It was shown that the Zimm-Bragg cooperativity parameter sigma is determined by the set of (delta-1) amino acid residues and so is nonlocal. An analytic expression for cooperativity parameters in a heteropolypeptide chain was obtained and numerical calculations showed that in case of heteropolypeptide with random primary structure the nonlocality of cooperativity parameter influenced the temperature dependence of helicity degree.