Figure 2.

Distribution of thermally accessible states. Y(N_f) = Σ_i(P_i²), which represents the inverse number of thermally accessible states available to the system, was computed for all values of N_f, and the result for SH3 and γ repressor is shown. The sharp peak near N_f ∼ 0.8 for the SH3 domain (solid line) indicates a drastic reduction in the number of accessible states late in folding that is also seen for CI-2, barnase, and Che Y. By contrast, λ-repressor (dotted line) does not exhibit such a drastic reduction in accessible states, suggesting a more plastic folding mechanism.