Abstract-Terahertz Absorption of illuminated Photosynthetic Reaction Center solution: a signature of photoactivation?

Ida Veronica Lundholm,   Weixiao Yuan Wahlgren,  Federica Piccirilli,   Paola di Pietro,   Annette Duelli,  Oskar Berntsson,   Stefano Lupi,   Andrea Perucchi and  Gergely Katona  

RSC Adv., 2014, Accepted Manuscript

DOI: 10.1039/C4RA03787A
Accepted 27 May 2014
First published online 29 May 2014

http://pubs.rsc.org/en/content/articlelanding/2014/ra/c4ra03787a#!divAbstract

Photosynthetic reaction centers develop a stable charge separated state upon illumination. To investigate the molecular vibrations associated with the illuminated state of a reaction center we recorded terahertz absorption spectra of the photosynthetic reaction center from Rhodobacter sphaeroides in the dark and upon illumination and observed a small, but significant THz absorption increase in the 20 to 130 cm-1 spectral region. Reaction centers show very similar terahertz absorption increase when solubilized in detergents and in a lipidic sponge phase indicating that the nature of the bulk solvent has limited influence on the vibrational spectrum. The absorption change of the isolated LM subunit is very similar to that of the intact reaction center. Through temperature control experiments we show that 89 % of the absorption change is likely attributed to the non-thermal activation of the protein molecules. These results indicate that picosecond molecular vibrations change primarily in the cofactors and/or in the evolutionary conserved core of the reaction centre upon illumination, whereas the nuclear motions of the H-subunit and the bulk solvent have limited impact on the terahertz spectral changes.