Resonance Raman spectroscopy of the photosystem II light-harvesting complex of green plants: a comparison of trimeric and aggregated states.

Resonance Raman spectroscopy was performed on photosystem II light-harvesting complex (LHCII) in trimeric and oligomeric states with various excitation conditions. From these studies, it can be concluded that the structure of LHCII is altered during the trimer/oligomer transition. These structural changes affect the conformation of a population of carotenoid within the complex, which becomes twisted in the oligomeric form. Moreover, the interactions assumed by a chlorophyll a and a chlorophyll b are modified during the oligomerization process. This induces the formation of an H-bond to a formyl group of a chlorophyll b molecule and to a keto group of a chlorophyll a molecule. The extent to which these H-bonds to chlorophyll relate to the formation of the quencher cannot yet be precisely established. However, the structural changes they evidence may play a role in the control of the energy flux by LHCII complexes.