Influences of cationic, anionic, and nonionic surfactants on alkaline-induced intermediate of bovine serum albumin

The formation of one molten globule-like intermediate of bovine serum albumin (BSA) at pH 11.2 has been established by circular dichroism (CD) spectra, fluorescence spectroscopy and ‘phase diagram’ approach. Three types of surfactants induced α-helical structure and resumed the tertiary structure of alkaline-induced BSA intermediate. The internalized tryptophans of the intermediate were exposed to a more polar environment in the presence of surfactants. Induction of both secondary and tertiary structures in alkaline-unfolded BSA was greater in the presence of 3.5 mM cetyltrimethylammonium bromide (CTAB) followed by 8.0 mM sodium dodecyl sulphate (SDS) and the least in 0.1 mM Tween-20. Maximum ANS binding was obtained in the presence of 0.1 mM Tween-20 followed by 8.0 mM SDS. The addition of 3.5 mM CTAB resulted in loss of ANS binding sites, suggesting the burial of hydrophobic patches.