Determination of the chromophore structures in the photoinduced reaction cycle of phytochrome.
The chromophore structures in the parent states Pr and Pfr as well as in the photocycle intermediate Lumi-R of oat phytochrome phyA are determined by comparison of the experimental resonance Raman spectra with calculated Raman spectra that have been obtained by density functional theory calculations (B3LYP) using scaled force fields. The spectra were calculated for various tetrapyrrole geometries including more than twenty different methine bridge isomers. For the parent states Pr and Pfr the best agreement in terms of vibrational frequencies, isotopic shifts, and Raman intensities was achieved with the ZZZasa and ZZEssa geometry, respectively. For the first intermediate Lumi-R, the chromophore geometry is concluded to be the ZZEasa configuration. These finding imply that the primary step of the photoactivation of phytochrome is the Z/E isomerization of the C-D methine bridge double bond, whereas the single bond remains in the anti conformation. The subsequent transition to the physiologically active state Pfr includes a (partial) single bond rotation of the A-B methine bridge.
Mroginski
Maria Andrea
MA
Technische Universität Berlin, Institut für Chemie, Sekr. PC 14, Strasse des 17. Juni 135, D-10623 Berlin, Germany.
Murgida
Daniel H
DH
von Stetten
David
D
Kneip
Christa
C
Mark
Franz
F
Hildebrandt
Peter
P
D001664:Biliverdine / Q000031:analogs & derivatives* / Q000737:chemistry; D008968:Molecular Conformation; D010777:Photochemistry; D010834:Phytochrome / Q000737:chemistry*; D013059:Spectrum Analysis, Raman
D010834:Phytochrome; C075811:phytochromobilin; D001664:Biliverdine