Oxygen-evolving complex reduced forms

Nature represents the blueprint for storing sunlight in the form of chemical fuels (such as sugars) by CO2 conversion. The primary steps of natural photosynthesis involve the absorption of sunlight and its conversion into separated electron/hole pairs. The holes of this wireless current are then captured by the oxygen-evolving complex (OEC) to oxidize water to oxygen (reaction 1) that allows the electrons that are captured by the photo system to reduce NADP (nicotinamide adenine dinucleotide phosphate) to NADPH (the reduced form of NADP, (reaction 2) (Kanan et al., 2008) [4]. 

For observing the function of Z, the main limitation has a kinetic origin since is absent, the radical-pair (P-680. r) decays by recombination, with a V/2 of about 30 ns (7). This is much faster than electron donation by Z which should be in the microsecond range. It has been found, however, that function can be reconstituted In some respect by addition of quinones (8,9). We have also found that DBMIB can reconstitute function (K.S., O.H. and P.M.. to be published), and we rely on that property to show that, upon addition of DBMIB, P-680 formed by a flash is re-reduced with a kinetic behaviour attributable to Z. according to our previous studies with chloroplasts (10.11). These results tend to show that Z is functional in at least a fraction of the (D1.D2) complexes (12) in this material where the oxygen-evolving enzyme is inactivated. 

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