Secondary structure of globular proteins at the early and the final stages in protein folding.

The ellipticities for an early transient intermediate in refolding observed by kinetic circular dichroism measurements at 220-225 nm for 14 different proteins are summarized, and the ellipticity values are compared with those for the final native proteins and also with the ellipticities expected from a physical theory of protein and polypeptide secondary structure. The results show that a substantial part of the protein secondary structure is in general formed in the earliest detectable intermediate in refolding and that the ellipticities in both the native and the intermediate states are consistent with the physical theory of protein secondary structure.