Energy transfer pathways in the peridinin chlorophyll-a protein complex as revealed by the near-infrared time-resolved spectroscopy

摘要

The peridinin chlorophyll-a protein (PCP) is a water-soluble light harvesting complex from dinoflagellates, with a pigment stoichiometry of 8 carotenoids (peridinin) and 2 chlorophyll-a (Chl-a) molecules. The crystal structure of PCP (Hofmann et al.1996) has provided a good basis for both experimental and theoretical studies of energy transfer pathways within the complex (Bautista et al. 1999a, Damjanovic et al. 2000, Krueger et al. 2001). These studies demonstrated high efficiency (88+-2 percent)of peridinin-chlorophyll energy transfer with a characteristic time constant of 2.3-3.2 ps. It was suggested that energy transfer took place predominantly from the peridinin S_1 state to the chlorophyll Q_y state (Bautista et al. 1999a), although more recent results were interpreted as partial energy transfer via peridinin S_2 state (Krueger et al. 2001). However, the lowest excited state of peridinin exhibits rather unusual behaviour, which was attributed to a state with charge-transfer (CT) characterin the excited state manifold lying close to the S_1 state (Bautista et al. 1999b). Dynamics of the peridinin CT state in solution was recently studied by near-infrared femtosecond (Zigmantas et al. 2001), but a role of the CT state in energy transfer between peridinin and Chl-a in PCP remains unclear. Here we apply near-infrared femtosecond spectroscopy to study dynamics of the lowest excited states of peridinin in the PCP complex. We address the important question whether the CT state of peridinin plays a role during energy transfer between peridinin and Chl-a in the PCP complex.