Kinetics of and intermediates in a photocycle branching reaction of the photoactive yellow protein from Ectothiorhodospira halophila.
We have studied the kinetics of the blue light-induced branching reaction in the photocycle of photoactive yellow protein (PYP) from Ectothiorhodospira halophila, by nanosecond time-resolved UV/Vis spectroscopy. As compared to the parallel dark recovery reaction of the presumed blue-shifted signaling state pB, the light-induced branching reaction showed a 1000-fold higher rate. In addition, a new intermediate was detected in this branching pathway, which, compared to pB, showed a larger extinction coefficient and a blue-shifted absorption maximum. This substantiates the conclusion that isomerization of the chromophore is the rate-controlling step in the thermal photocycle reactions of PYP and implies that absorption of a blue photon leads to cis-->trans isomerization of the 4-hydroxy-cinnamyl chromophore of PYP in its pB state.
Hendriks
J
J
Laboratory for Microbiology, E.C. Slater Institute, BioCentrum, University of Amsterdam, The Netherlands.
van Stokkum
I H
IH
Crielaard
W
W
Hellingwerf
K J
KJ
D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D002841:Chromatiaceae / Q000737:chemistry* / Q000378:metabolism*; D003624:Darkness; D007700:Kinetics; D007834:Lasers; D010782:Photolysis; D020283:Photoreceptors, Microbial; D013056:Spectrophotometry, Ultraviolet; D013997:Time Factors
D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; C050162:photoactive yellow protein, Bacteria