EVIDENCE FOR TRANS-CIS ISOMERIZATION OF THE P-COUMARIC ACID CHROMOPHORE AS THE PHOTOCHEMICAL BASIS OF THE PHOTOCYCLE OF PHOTOACTIVE YELLOW PROTEIN

Analysis of the chromophore p-coumaric acid, extracted from the ground state and the long-lived blue-shifted photocycle intermediate of phot oactive yellow protein, shows that the chromophore is reversibly conve rted from the tr ans to the cis configuration, while progressing throu gh the photocycle, The detection of the trans and cis isomers was carr ied out by high performance capillary zone electrophoresis and further substantiated by H-1 NMR spectroscopy. The data presented here establ ish the photo-isomerization of the vinyl double bond in the chromophor e as the photochemical basis for the photocycle of photoactive yellow protein, a eubacterial photosensory protein, A similar isomerization p rocess occurs in the structurally very different sensory rhodopsins, o ffering an explanation for the strong spectroscopic similarities betwe en photoactive yellow protein and the sensory rhodopsins. This is the first demonstration of light-induced isomerization of a chromophore do uble bond as the photochemical basis for photosensing in the domain of Bacteria.