Terahertz Absorption change in Photosynthetic\ud Reaction Center upon photoactivation

摘要

Photosynthetic reaction center is a membrane protein\udwhich plays an important role in converting solar energy into\udchemical energy. Upon continuous illumination a charge\udseparation occurs within the protein which is stable for\udseveral seconds [1]. The stability of this state is very\udimportant to protect the protein against the release of excess\udheat and an instable radical due to charge recombination.\udAbsorption of terahertz radiation corresponds to the\udexcitation of large vibrations in the protein and is thus suitable\udfor studying its different dynamical states. Here we recorded\udterahertz absorption spectra of the dark and illuminated state\udof reaction centre from the purple membrane bacteria\udRhodobacter sphaeroides\udto investigate the stability of the\udcharge separated state. The difference terahertz absorption\udspectra show an overall increase in absorption for the\udilluminated state in the 30-130 cm\ud-1\udspectral region. By\udsimulating and fitting a theoretical terahertz spectrum of\udreaction center from an elastic network model we were able to\udinvestigate the effect of charge separation and conformational\udchanges within the interaction network. We find that a more\udloose interaction network in the photoactivated state of the\udprotein is the most probable cause of the absorption increase.