Basis for large differences in the cooperativity of the formation of antiparallel β‐sheets and clusters of interacting α‐helices in isolated chains

Configuration partition functions that describe the intramolecular formation of antiparallel β‐sheets and clusters of antiparallel interacting α‐helices are very nearly of the same form. They can be interconverted by a simple change in notation and the addition of one weighting factor for each cluster of interacting α‐helices. This extra weighting factor is the Zimm–Bragg σ which must be less than one. When it is assigned a reasonable numerical value, it plays an important role in the determination of the nature of the transition from the disordered chain to the ordered structure. It causes the formation of clusters of interacting α‐helices to be more cooperative than the formation of antiparallel β‐sheets in isolated chains.