The binding distance of fluorescein to BSA and hydrodynamic radius of BSA in 1-propanol (NPA)-water and 2-propanol (IPA)-water mixtures were determined by a fluorescence quenching technique and dynamic light scattering measurements respectively and utilized to investigate the effects of NPA and IPA on the conformation of protein in aqueous solutions. The results showed that both binding distance of fluorescein to BSA and hydrodynamic radius of BSA decreased at first and then increased with increasing concentrations of NPA and IPA, suggesting that both NPA-water and IPA-water mixtures at high concentrations destabilize the native structure of protein, whereas at low concentrations slightly stabilize the native state of protein. It was also found that the binding distance in aqueous NPA was larger than that in aqueous IPA at the same concentration, whereas the hydrodynamic radius of BSA in the former was smaller than that in the latter, indicating that the hydrophobic part of NPA with no branch worked effectively for hydrophobic interaction with the nonpolar group of protein, and that IPA had a tendency to interact with the hydrophilic groups on the surface of protein due to its relatively weak hydrophobicity.

Key words: bovine serum albumin, 1-propanol, 2-propanol, fluorescence quenching, dynamic light scattering