Circular Dichroism Quantitative Estimate of α-Helix Content of Human Serum Albumin in the Presence of NaSCN, Urea and KCl at Various pH
Conformational changes in human serum albumin (HSA) in the presence of several concentrations of NaSCN, urea and KCl at various pH were examined quantitatively on the basis of rotational strength at 208 nm by means of circular dichroism (CD). The α-helix content of HSA was markedly dependent on concentrations of NaSCN and urea, but not on KCl. However, when these salts coexisted with a concentration of hydrogen ion in the albumin solution, the α-helix content of HSA was markedly dependent on all these salts. Among these salts, the distortion power of NaSCN on the conformational stability of the peptide backbone was undoubtedly several hundred times stronger than that of the other salts. Conformational changes in HSA were scarcely observed at pH 4.8-10.0 under a constant concentration of each salt, but were more dependent on pH outside of the above range regardless of salt. The α-helix content of highly denaturated HSA in solution containing a high salt concentration was less dependent on the hydrogen ion concentration, while at a low concentration of each salt, it was pH dependent, as if there was no salt.