Contrasting the excited-state dynamics of the photoactive yellow protein chromophore: Protein versus solvent environments

Wavelength- and time-resolved fluorescence expts. have been performed on the photoactive yellow protein, the E46Q mutant, the hybrids of these proteins contg. a nonisomerizing "locked" chromophore, and the native and locked chromophores in aq. soln. The ultrafast dynamics of these six systems is compared and spectral signatures of isomerization and solvation are discussed. We find that the ultrafast red-shifting of fluorescence is assocd. mostly with solvation dynamics, whereas isomerization manifests itself as quenching of fluorescence. The obsd. multiexponential quenching of the protein samples differs from the single-exponential lifetimes of the chromophores in soln. The locked chromophore in the protein environment decays faster than in soln. This is due to addnl. channels of excited-state energy dissipation via the covalent and hydrogen bonds with the protein environment. The obsd. large dispersion of quenching timescales obsd. in the protein samples that contain the native pigment favors both an inhomogeneous model and an excited-state barrier for isomerization. [on SciFinder (R)]