Associated Emission Spectra of Proteins

An obvious application of time-resolved proton fluorescence is to resolve die contributions of individual tryptophan residues in multi-tiyptophan proteins. This is accomplished Ity measuring die intensity decay across die emission spectrum of die protein, resulting in wavelengdi-dependent data. 

As implied by this equation, a typical, but not necessarily correct, assumption is diat die decay times are independent of wavelen. The wavelengdi-d ioidoit values Xj(X) are then used Id construct die emission spccm (/j(X)] associated vradi cadi spedes. 

In this expression, /(X) is flw steady-state emission spec-tnun. These spectra 7i(X) are called decay-associated plectra (DAS) bwatise /i(X) represents die emission spectnun of the component emitting with lifetime Ti. 

DAS have been determined for a number of proteins, with an emphasis on proteins which contain two tryptophan residues. In these cases one hopes that each tryptophan will display a single decay time, so that the I S represent the emission spectra of the individual residues. One example is provided by a study of yeast 3-phospho-glycerate kinase (3-FGK), which has two tryptophan residues. Rom a number of pH- and wavelengdi-dependent measurements, the 0.6-ns component in die decay was associated with one residue, and the 3.1- and 7.0-ns components were associated widi die second tryptophan residue. The wavelength-dependent intensity decays were 

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