Relaxational Shift of Steady-State Spectra

There are substantial difficulties in the interpretation of temperature-dependent shifts of protein spectra because of the thermal lability of proteins and the possibility of temperature-dependent conformational transitions. Low-temperature studies in aqueous solutions revealed that for many of the proteins investigated the observed shifts of the fluorescence spectra within narrow temperature ranges were probably the result of cooperative conformational transitions, and not of relaxational shifts/100 1 Spectral shifts have also been observed for proteins in glass-forming solvents, 01) but here there arise difficulties associated with the possible effects of viscous solvents on the protein dynamics. 

Short-wavelength spectral shifts may also be observed for proteins under conditions of dynamic quenching by oxygen and acrylamide. However, the existing data do not yield reliable estimates of rRJf, under the initial conditions, xR xF, then the quenching experiments do not allow v. to be determined and Eq. (2.9) cannot be applied. 

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