Resolution of Spectral and Lifetime Heterogeneity of Tryptophan Fluorescence in Bacteriorhodopsin

Abstract

Abstract— The picosecond time‐resolved fluorescence decay of bacteriorhodopsin (BR) was analyzed by the maximum entropy method. Results showed five distributions of lifetimes indicating at least five decay components. A wavelength‐dependent study of emission decay of BR was carried out in the wavelength region from 310 to 390 nm. The decay at each wavelength was resolvable into four decay components by the discrete exponential analysis. The three short lifetime components (100 ± 20 ps, 400 ± 50 ps and 1.0 ± 0.1 ns) were independent of wavelength, whereas the longest lifetime component was wavelength dependent (varying from 4.1 ns at 310 nm to 5.7 ns at 390 nm). These results are inconsistent with the existing model of associating the fluorescence of bacteriorhodopsin with two or four lifetime components. An attempt is made to associate the five decay components with the emitting tryptophans of BR.

Intrinsic Time- and Wavelength-Resolved Fluorescence of Oligonucleotides: A Systematic Investigation Using a Novel Picosecond Laser Approach

“…Therefore, the same numerical reconvolution routine as above is used to evaluate the time-dependent anisotropy from fits to the difference function D exp (t) and the intensity sum function S exp (t) with It might be argued that more than two exponential decay functions might need to be considered for a valid description of the fluorescence behavior of DNA and other biomolecules. In previous work, single-exponential fits 41 as well as fits with four and more exponentials have been used, 16,50,51 and some authors 51,52 rely on the maximum entropy method. 53 In our study on oligonucleotides, we have been limited by the signal-to-noise level to extract more than two meaningful lifetime components.…”

The study of terbium regenerated bacterirhodopsin

“…The partially quenched tryptophans are associated with the shot-lived component (0.5 0.9 ns). The long-lived component (3.5 5.0 ns) is found to have the same lifetime as that of retinal-free protein and this component is associated with the unquenched tryptophans [18] . The different Trps have different lifetimes according to their microenvironments and conditions.…”

“…It has been proposed that the most of Trp residues are buried in the internal region of the membrane, these fluorescences are quenched by retinal chromophore through energy transfer. Surface Trp residues such as Trp-10, Trp-12 were recently specified as the candidates for the unquenched or partly quenched Trp residues [18] .…”