Biophysical and biochemical studies of the structure and function of Photosystem II
In the photosynthetic reactions, energy from light is stored as chemical energy. In the oxygenic photosynthesis this process occurs in the thylakoid membranes of green plants, alga and cyanobacteria. The electrons which needed to store the energy in the chemical form are derived from water, the most abundant substance in biosphere. Water is oxidized to dioxygen, electrons and protons by Photosystem II, a very large enzyme. Photosystem II works at extremely high redox potentials and carries out unique electron transfer reactions. The active components are the Ca-Mn-cluster, protein-bound Tyrosines, Quinones and a chlorophyll component named P680.
In the project the function of these components and the mechanism for the oxidation of water to dioxygen are investigated. In the experiments we apply various biochemical treatments, illumination procedures and site-directed mutagenesis to study these redox components in the Photosystem II reaction center. We are using optical, fluorescence and magnetic resonance spectroscopy.
Our major spectroscopic tool is EPR (electron paramagnetic resonance) that is particularly suited to study photosynthetic electron transfer reactions. We are using different continuous wave and pulsed EPR techniques to study how the Tyrosine radicals oxidize the Ca-Mn-cluster during oxygen evolution. For this, we combine EPR spectroscopy and powerful laser flashes to investigate the light-induced turnover of the Photosystem II.