A model of alpha-helical distribution in proteins.

It is shown that alpha-helical content of eleven proteins is well correlated with alanine plus leucine content. These residues, taken singly or together, are to a first approximation randomly distributed in the four proteins whose tertiary structures have been determined (i.e., myoglobin, lysozyme, ribonuclease, alpha-chymotrypsin). A model based on the concept that certain randomly distributed residues specifically participate in helix nucleation is shown to be in reasonable agreement with the presently published structures.