Photosystems overview

Figure 12.8 The Z scheme, an overview of the flow of electrons during the light-dependent reactions of photosynthesis. ED and EA refer to the electron donors and acceptors of the two photosystems, respectively...

I have presented an overview of the current state-of-the-art in studies of the Mn complex in photosystem II. There are many unresolved questions and a clear picture of the structure and function of Mn in photosynthetic water oxidation is still not available. One useful approach to help determine the structure of the Mn complex in photosystem II involves the synthesis and characterization of Mn model complexes for comparison with the properties of the Mn complex in photosystem II. Recently, several tetrameric high-valent Mn-oxo complexes have been reported (see the chapter in this volume by G. Christou). Further characterization of existing and new high-valent tetrameric Mn-oxo model complexes, especially EPR and EXAFS measurements, will no doubt help clarify the present uncertain picture of the structure of the Mn complex in photosystem II. 

Goussias, C., Boussac, A., Rutherford, A. W. (2002). Photosystem II and photosynthetic oxidation of water an overview. Philosophical Transactions of the Royal Society B Biological Sciences, 357, 1369—1381. 

The authors begin with the basic equation of photosynthesis and an overview of the process. Next comes a description of the chloroplast, of chlorophyll, and of the relatively simple reaction center from a photosynthetic bacterium. They then describe the overall structures, components, and reactions of photosystems II and I, and the cytochrome bj complex, including the absorption of fight, charge separation, electron-transport events, and the evolution of O2. They explain how these light reactions lead to the formation of proton gradients and the synthesis of ATP and NADPH. 

The objectives of the study presented in this paper were to observe and characterize phototransients produced by laser excitation of natural waters and humic substance (HS) solutions. The photosystems were studied on two scales. On the laboratory scale pulsed laser flash photolysis was used to study the time resolved and spectral behavior of the photochemical transients. Studies to Identify and quantify the transients Included adding energy and electron acceptors and model compounds to the solution and varying parameters such as pH, metal, and oxygen content. On the field scale laboratory data taken at solar actinic wavelengths Is extrapolated using published solar photon fluxes to predict environmental effects of the phototransients studied In this work. This paper thus contains an overview of many experiments performed over four years (16). 

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