Upper limit of the time scale for diffusion and chain collapse in chymotrypsin inhibitor 2

The rates of folding of wild-type chymotrypsin inhibitor 2 (CI2) (t(1/2) = 12 ms) and of faster (t(1/2) = 2 ms) and slower (t(1/2) = 350 ms) folding: mutants are accelerated in parallel by increasing concentrations of sucrose , despite the increases in viscosity. Al: a viscosity 26 times that of wate r, the folding rate constant of wild-type CI2 is accelerated four-fold (t(1 /2) = 2.7 ms). From this, we can estimate that the diffusional chain collap se in CI2 occurs in less than 100 mu s in water, and is not rate-determinin g in folding.