The lanthanide-induced N = to F transition and acid expansion of serum albumin.

Serum albumin exists in the native or N conformation between pH 5 and 7. As the pH is lowered from 5 to 3.5, the protein undergoes a conformational change resulting in expansion, known as the N = to F (partially acid expanded) transition. As the pH is lowered still further to 2, the protein continues to expand. In the present study, using the techniques of circular dichroism, fluorescence, and UV difference spectroscopy, lanthanide ions at concentrations between 1-30 mM have been shown to produce both changes in the albumin structure analogous to the N = to F transition and acid expansion of bovine serum albumin at a constant pH near 6.