HELIX-COIL TRANSITIONS IN SPECIFIC SEQUENCE BIOPOLYMERS.

The theory of helix-coil transitions in specific sequence biological macromolecules is reviewed. The importance of the cooperative nature of the transition (resulting in the tendency for long helical sequences to exist in the transition region) is stressed in that heterogeneity of polymer composition (hence heterogeneity of helix stability) tends to more or less localize long sequences of helix producing a pronounced profile of helical probability. The appropriate thermodynamic parameters and the resulting nature of the transitions for DNA, collagen, and proteins are compared. Some new calculations are given for carboxypeptidase A that includes heterogeneity in both the helix-coil parameters sigma and s.