Fluorescence anisotropy of photoactive yellow protein (PYP) and related systems: Is the low-lying excited state of the PYP quasi-degenerate?

摘要

Photoactive Yellow Protein (PYP) is a blue light photoreceptor responsible for the negative phototaxis of the purple sulfur bacterium Ectothiorhodospira halophila. Photoexcitation of PYP with a blue light triggers a photocycle that involves several intermediate states. Trans/cis photoisomerization of its chromophore (Thcoumaric acid) buried in the protein has been identified as the overall primary event triggering its photocycle.However, the complex ultrafast dynamics of PYP's photocycle is not fully understood and efforts are made to separate and characterize the intra- and interchromophore factors affecting the early processes. Ideally, such studies should be curried out in environments from gas to solution and protein phases to elucidate how the protein environment controls and directs the primary photodynamics. Recently, high-resolution gas-phase fluorescence excitation experiments were performed on the neutral form of PYP's pCA chromophore.