Validity of the “two‐state” hypothesis for conformational transitions of proteins

Abstract The theory, character, and properties of cooperative transitions are developed with special reference to the abrupt changes of state which occur in protein solutions. Comparisons of helix–coil processes and protein conformational reactions show that though cooperation dominates both of these processes, there are important differences. Tests of two types for the validity of the two‐state approximation are presented with specific applications to proteins. Available experimental evidence demonstrates that the thermally induced reversible transitions of ribonuclease, α‐chymotrypsin, and chymotrypsinogen A under conditions thus far examined are two‐state processes.