3 Photosynthetic water oxidation: The function

The solar energy accumulated by photosynthesis over billions of years is the sole source of energy available on Earth. Photosystem II (PSII) uses the sunlight to split water, an energetically unfavorable reaction where electrons and protons are extracted from water and oxygen is released as a by-product. Understanding this process is crucial for the future development of clean, renewable and unlimited energy sources, which can use sunlight to split water and produce hydrogen and electricity. In order to do so we need to understand how this is solved in plants. I have been focusing on the role of two lumenal proteins associated with the thylakoid membrane PsbO and Cah3, in the water oxidation process. Convincing evidences have been presented supporting the hypothesis that bicarbonate acts as a proton acceptor in the water splitting process in PSII and the lumenal carbonic anhydrase, Cah3, supplies bicarbonate required for this function. The PsbO protein, an important constituent of the water