Study of the “Molten Globule” Intermediate State in Protein Folding by a Hydrophobic Fluorescent Probe

Binding of the hydrophobia 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, α-helical, or β-structural hydrophilic homopolypeptides. The possibility of using ANS for the study of equilibrium and kinetic molten globule intermediates is demonstrated, with carbonic anhydrase, β-lactamase, and α-lactalbumin as examples