Characterization of human serum albumin forms with pH. Fluorescence lifetime studies.

Fluorescence lifetimes of human serum albumin (HSA) tryptophan 214 residue were measured in solution at different pH (from 2 to 12). The results indicate that tryptophan emission occurs with three lifetimes at all pH. However, lifetimes and pre-exponential values are dependent on the pH and thus on the protein form. Three different protein populations have been differentiated: one population for pH 2 and 3 (extended form), the second one from pH 4 to 9 containing HSA migrating (F), normal (N) and basic (B) forms. Another type of population is obvious for pH higher than 9, characterizing the aged (A) form of HSA. Copyright 2009. Published by Elsevier B.V.