Binding of the hydrophobic fluorescent probe, 1-anilino-naphthalene-8-sulfonate (ANS), to synthetic polypeptides and proteins with a different structural organization has been studied. It has been shown that ANS has a much stronger affinity to the protein "molten globule" state, with a pronounced secondary structure and compactness, but without a tightly packed tertiary structure as compared with its affinity to the native and coil-like proteins, or to coil-like, alpha-helical, or beta-structural hydrophilic homopolypeptides. The possibility of using ANS for the study of equilibrium and kinetic molten globule intermediates is demonstrated, with carbonic anhydrase, beta-lactamase, and alpha-lactalbumin as examples.

The kinetics of refolding of bovine carbonic anhydrase B was studied by a variety of methods over a wide range of times (from milliseconds to hours). It has been shown that protein refolding proceeds through three stages. At the first stage (tl/2~0.03 s) hydrophobic clusters and a compact state of the chain are formed. At the second stage (tl,'2 ~ 140 s) hydrophobic clusters are desolvated and the rigid native-like hydrophobic core is formed. At the third stage (tl/2 ~ 600 s) the native active protein is formed.

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