Spectral demonstration of structural transitions in albumins

Abstract

Several spectral methods (UV absorbance, fluorescent and FTIR spectroscopy) were applied to reveal the alterations in the secondary and tertiary structures of human serum albumin (HSA) in water solutions under various conditions (pH, protein concentration, ethanol and n-propanol addition). The structural transitions well known for defatted HSA at 1.5 < pH < 13 are observed for HSA in a complex with long-chain fatty acids in the molar ratio about 1:1. The changes of HSA ζ-potential during the protein isomerizations induced by the variation of pH are traced. It is shown that HSA does not completely lose its secondary structure at extreme alkaline or acidic solutions, which indicates that at these conditions HSA takes the “molten globule” conformation. A comparison of aggregation processes of HSA and ovalbumin in neutral water and 0.15 M NaCl solutions reveals that OVA aggregation is preceded by a partially denaturated state of the protein, whereas an intermediates of HSA aggregates are close to the native state of the protein. The aliphatic alcohols disturb the tertiary structure of HSA, but stabilize its secondary structure. This effect increases with the rise of the alcohol hydrophobicity.