PARENT SESSION
Posters P4Aa Chlorophyll and bilin based antenna systems. Abstracts (239-271)

Energy transfer in reconstituted light-harvesting complex II of green plants. Miguel Palacios^*,1, Jörg Standfu², Mikas Vengris¹, Werner Kühlbrandt², Herbert van Amerongen³, Rienk van Grondelle¹, ¹ Faculty of Sciences, Department of Biophysics, Vrije Universiteit, Amsterdam, The Netherlands² Max-Plank Instituut für Biophysik, Abteilung Strukturbiologie, Frankfurt am Main, Germany³ Laboratory of Biophysics, Department of Agrotechnology and Food Sciences, Wageningen, The Netherlands

ABSTRACT- We have performed femtosecond transient absorption experiments on native and reconstituted light-harvesting complex II from green plants, which allowed us to accurate resolve the energy transfer dynamics in this system. Native trimers are composed of a mixture of the three genes lhcb1, lhcb2 and lhcb3, whereas reconstitution led to complexes where only one of the genes was overexpressed: homotrimers of the genes lhcb1 and lhcb2 and monomers of lhcb3. The kinetics, obtained with low intensity excitation laser pulses centered at 650 nm (mainly Chl b) and 662 nm (Chl a), are similar for all the complexes and show that excitation energy transfer from Chl b to Chl a includes sub-picosecond (250–600 fs) and slower (picosecond) migration of the excited states, whereas selective excitation of the Chl a absorption bands peaking at ∼660 nm leads to mainly slow processes. The final equilibration time between the Chl a pool takes place in ∼20 ps. The major differences between native and reconstituted complexes are observed at around 660 nm, where an enhanced pump-probe signal is observed for the reconstituted complexes, which we ascribe to the increased absorption cross-section observed in the absorption spectrum at those wavelengths. The competition between fast and slow processes observed can be very well described in the context of the Redfield Theory.

KEY WORDS: lhcii, reconstituted, energy transfer, transient absorption