Picosecond Tryptophan Fluorescence of Human Blood Serum Orosomucoid

The state of three tryptophyl residues in human serum orosomucoid was estimated by prediction methods based on parameters characterizing their hydrophobicity either directly, or in terms of buried surfaces of the individual amino acid residues. It is shown that tryptophan 25 is the most buried, while Trp 160 is the most exposed to the solvent. Trp 122 is in this respect in an intermediate state. The fluorescence decay behaviour was determined using a picosecond single photon counting system. The multiwavelength data were analyzed using a global analysis as well as a distribution of lifetimes program. Both procedures yielded the existence of four wavelength independent lifetimes (0.22 ns, 1.0 ns, 2.5 ns, and 8.4 ns). A tentative assignment of the decay associated spectra of the four components to the three individual tryptophans is presented.