Time-resolved fluorescence studies on site-directed mutants of human serum albumin

Human serum albumin (HSA) contains a single tryptophan residue at position 214. The emission properties of tryptophan 214 from recombinant albumins, namely, normal HSA, FDH-HSA and a methionine 218 HSA were examined. In all cases, the excited state lifetimes were best described by a two component model consisting mainly of a Lorentzian distribution. The centers of these distributions were 5.60 ns for HSA, 4.23 ns for FDH-HSA, and 6.08 ns for Met-218 HSA. The global rotational correlation times of the three HSAs were near 41 ns while the amplitude and rate of the local motion varied. These changes in the lifetimes and mobilities suggest perturbation in the local protein environment near tryptophan 214 as a consequence of the amino acid substitutions.