Abstract:

The binding distance of benzidine to hemoglobin (Hb) and the hydrodynamic radius of Hb in urea-water mixtures were determined by fluorescence quenching and dynamic light scattering, respectively. These data, combined with fluorescence spectra and absorption spectra, were utilized to investigate the interaction between urea and protein as well as its influence on the conformation of protein in aqueous solutions. The results indicated that urea accumulated on the surface of the protein due to its ability to displace water molecules in the solvation shell and to form hydrogen-bond with peptides and hydrophilic side chains, which exhibited a complex influence on protein conformation. It was evident that urea-water mixtures at high urea concentration destabilized the protein conformation whereas those at low urea concentration promoted a more compact one. In the mixtures at high urea concentration, the heme cavity of Hb was found to be of unfolded structure, however similar to the molten globubar state.

Key words: Hemoglobin, Urea, Fluorescence spectrum, Dynamic light scattering, Absorption spectrum