title: Interpretation of fluorescence decays using a power-like model.
abstract: A power-like decay function, characterized by the mean excited-state lifetime and relative variance of lifetime fluctuation around the mean value, was applied in analysis of fluorescence decays measured with the aid of time-correlated single photon counting. We have examined the fluorescence decay, in neutral aqueous medium, of tyrosine (L-tyrosine and N-acetyl-L-tyrosinamide), and of the tyrosine residues in a tryptophan-free protein, the enzyme purine nucleoside phosphorylase from Escherichia coli in a complex with formycin A (an inhibitor), and orthophosphate (a co-substrate). Tryptophan fluorescence decay was examined in neutral aqueous medium for L-tryptophan, N-acetyl-L-tryptophanamide, and for two tryptophan residues in horse liver alcohol dehydrogenase. To detect solvent effect, fluorescence decay of Nz-acetyl-L-tryptophanamide in aqueous medium was compared with that in dioxan. Hitherto, complex fluorescence decays have usually been analyzed with the aid of a multiexponential model, but interpretation of the individual exponential terms (i.e., pre-exponential amplitudes and fluorescence lifetimes), has not been adequately characterized. In such cases the intensity decays were also analyzed in terms of the lifetime distribution as a consequence of an interaction of fluorophore with environment. We show that the power-like decay function, which can be directly obtained from the gamma distribution of fluorescence lifetimes, is simpler and provides good fits to highly complex fluorescence decays as well as to a purely single-exponential decay. Possible interpretation of the power-like model is discussed.
authors.affiliation: Department of Biophysics, Institute of Experimental Physics, University of Warsaw, Warsaw, Poland.
authors.forename: Jakub
authors.initials: J
authors.lastname: Włodarczyk
authors.forename: Borys
authors.initials: B
authors.lastname: Kierdaszuk
mesh_terms: D003198:Computer Simulation; D005453:Fluorescence; D005573:Formycins / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D006207:Half-Life; D008027:Light; D008956:Models, Chemical; D013050:Spectrometry, Fluorescence / Q000379:methods*; D014364:Tryptophan / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry* / Q000528:radiation effects; D014443:Tyrosine / Q000032:analysis / Q000737:chemistry* / Q000528:radiation effects
chemical_list: D005573:Formycins; D014443:Tyrosine; C006392:N-acetyltryptophan; C034550:formycin; D014364:Tryptophan