Kinetic refolding reactions of ferricytochrome c and β‐lactoglobulin have been studied by stopped‐flow circular dichroism by monitoring rapid ellipticity changes of peptide backbone and side‐chain chromophores. In both proteins, a transient intermediate accumulates within the dead time of stopped‐flow mixing (18 ms), and the intermediate has an appreciable amount of secondary structure but possesses an unfolded tertiary structure. It is suggested that the rapid formation of a secondary structure framework in protein folding is a common property observed in a variety of globular proteins.

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