Shallow sink in an antenna pigment system of photosystem I of a marine centric diatom, Chaetoceros gracilis, revealed by ultrafast fluorescence spectroscopy at 17 K.

The ultrafast fluorescence dynamics of photosystem I (PS I) purified from a marine centric diatom, Chaetoceros gracilis, at 17 K was studied using fluorescence up-conversion and streak-camera setups. The experiments were done for two kinds of sample preparations containing different amounts of the peripheral antenna proteins, the fucoxanthin−chlorophyll (Chl) binding proteins associated with PS I (FCPI). Upon excitation at 430 nm, which selectively excites Chl a mainly contained in the core complex, the fluorescence dynamics of both samples was roughly expressed by four decay-associated spectra (DASs) with time constants of ca. 5, ca. 22, ca. 100, and ca. 400 ps. These DAS components have corresponding counterparts in the results of a previous study of Thermosynechococcus elongatus PS I (Shibata et al. J. Phys. Chem. B 2010, 114, 2954) except for that with a time constant of ca. 22 ps. The similar distribution of the time constants suggests a shared light-harvesting pathway by PS I of these two organisms....