Slow Energy Transfer from the Core Antennas CP43 and CP47 to the PSII RC Studied by Femtosecond Mid-Infrared Spectroscopy

Abstract

The core of Photosystem II (PSII) of green plants contains the reaction center (RC) proteins D1D2-cytb559 and two core antennas CP43 and CP47. We have used time-resolved visible pump/mid-infrared probe spectroscopy in the region between 1,600 and 1,800 cm−1 to study the energy transfer and charge separation events within PSII cores. The absorption difference spectra in the region of the keto and ester chlorophyll modes show spectral evolution with time constants of 3 ps, 27 ps, 200 ps and 2 ns. Comparison of IR difference spectra obtained for the isolated antennas CP43, CP47 and the D1D2-RC with those measured for the PSII core allowed us to identify the features specific for each of the PSII core components. We conclude that the kinetic model proposed earlier for the energy and electron transfer dynamics within the PSIIRC (Groot et al. 2005), plus two slowly energy transferring antennas C43 and CP47 explains the complex excited state and charge separation dynamics in the PSII core very well.