ABSTRACT
Human serum albumin consists of a single polypeptide of 585 amino acid residues with 1 Trp residue. In the present work, we measured fluorescence lifetimes of the protein in both native and denatured states. The results indicate that Trp emission occurs with three lifetimes in both states. Lifetimes values and contribution to the global emission decay differ between the two states. Data are interpreted as the results of an emission occurring from three substructures of the tryptophan formed in the excited state. Two of these substructures are already present for the tryptophan free in solution. The third lifetime is the result of the interaction between the tryptophan residue and surrounding microenvironment. The populations of these substructures characterized by the pre-exponential parameters of the fluorescence lifetimes are dependent on the fluorophore microenvironment and on the global protein structure.
Subject(s)
Fluorescence , Proteins/chemistry , Serum Albumin/chemistry , Tryptophan/chemistry , Albumins , Humans , Protein Denaturation , SolutionsABSTRACT
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.
