Investigation on the Thermodynamic Dissociation Kinetics of Photosystem II Supercomplexes To Determine the Binding Strengths of Light-Harvesting Complexes.

The photosystem II (PSII) supercomplex splits water utilizing light energy and is composed of a core dimer complex surrounded by light-harvesting complexes (LHCs). In green algae, the major LHCs which are LHCII trimers have thus far been categorized into strongly, moderately, or loosely binding LHCII trimers based on their predicted binding to core complexes. However, the binding energies have been indirectly predicted based on the presence or absence of LHCII trimers in the PSII supercomplex under electron microscopy and have not been determined experimentally. In this study, we investigated the binding of LHCII trimers by analyzing thermodynamic dissociation kinetics using isolated PSII supercomplexes. We identified two activation energies for dissociation of LHCII trimers: 54 ± 19 and 134 ± 8 kJ/mol. This result indicated the types of intermolecular interactions between LHCII trimers and core complexes.