Watersplitting enzyme

The reaction-center proteins for Photosystems I and II are labeled I and II, respectively. Key Z, the watersplitting enzyme which contains Mn P680 and Qu the primary donor and acceptor species in the reaction-center protein of Photosystem II Qi and Qt, probably plastoquinone molecules PQ, 6-8 plastoquinone molecules that mediate electron and proton transfer across the membrane from outside to inside Fe-S (an iron-sulfur protein), cytochrome f, and PC (plastocyanin), electron carrier proteins between Photosystems II and I P700 and Au the primary donor and acceptor species of the Photosystem I reaction-center protein At, Fe-S a and FeSB, membrane-bound secondary acceptors which are probably Fe-S centers Fd, soluble ferredoxin Fe-S protein and fp, is the flavoprotein that functions as the enzyme that carries out the reduction of NADP+ to NADPH. 

In this article, we offer a brief and select overview of the literature on the atomic and electronic structure of the watersplitting enzyme,the chemical basis of its catalysis, and insights learned from functional model complexes. Citations cover the main review articles that are available rather than primary works. 

GW Brudvig and WF Beck (1992) Oxidation-reduction and ligand substitution reactions of the oxygen-evolving center of photosystem //, in Manganese Redox Enzymes (VL Pecararo, ed) VCH Publ. pp. 119-140 G Renger (1972) The action of2-anilinothiophenes as accelerators of the deactivation reactions in the watersplitting enzyme system of photosynthesis. Biochim Biophys Acta 256 428-439... 

The above mentioned considerations have shown that the photosynthetic oxygen evolution occurs within functionally isolated entities, the watersplitting enzyme systems Y. Thus, the systems Y can be suggested as being a highly specialized microscopic... 

Furthermore, it should be mentioned that in analogy to the philogenetic evolution also in the ontogenesis the formation of the watersplitting enzyme system Y appears to be the last step of the development of algae and higher plants117,118. ... 

Fig. 8. Simplified free energy diagram of the photosynthetic electron transport chain (for details see Ref.27, 69X For the sake of simplicity only the reduced forms of the corresponding redox carriers are given. The electronic excitations are symbolized by thick open arrows, thermal redox reactions in the dark are indicated by thin arrows. Abbreviations Cyt fre(j = reduced cytochrome f, NADPH = reduced nicotinamide adenine dinucleotidphosphate, PCjgj = reduced plastocyanine, PQH2 = plastohydroquinone, Xf and X 320- are the reduced forms of the primary electron acceptor of C[ and Qj, respectively [see Eq. (14a, b)l, Y = watersplitting enzyme system...

Thus, cytochrome oxidase can be envisaged as to be the functional counterpart of the watersplitting enzyme system Y, extensively discussed in 4.2.2. 

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