Femtosecond-picosecond fluorescence studies on excited state dynamics of photoactive yellow protein from Ectothiorhodospira halophila

Dynamics of photochemical processes of photoactive yellow protein (PYP) which functions as a photoreceptor for a negative phototactic response of the bacteria has been studied by fs-ps fluorescence up-conversion technique. Fluorescence decay curvs were nonexponential and initial main components have time constants of several hundreds fs to a few ps. The decay processes were interpreted as due to the twisting around vinyl of p-coumaric acid chromophore leading to trans/cis isomerization and were similar to those of bacteriorhodopsin despite the quite different chromophore, except that the reaction is somewhat slower in PYP. Reaction mechanisms were discussed in comparison with those of rhodopsins.