FEMTOSECOND-PICOSECOND FLUORESCENCE STUDIES ON EXCITED-STATE DYNAMICSOF PHOTOACTIVE YELLOW PROTEIN FROM ECTOTHIORHODOSPIRA-HALOPHILA

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