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Transcript
Photosynthesis in cyanobacteria and plants Plants and cyanobacteria use the reducing power generated by the light-driven oxidation of H2O to produce NADPH this is an uphill battle and photosynthesis therefore requires at least 810 photons of visible light to produce one molecule of oxygen Two processes are involved in photosynthesis (usually depicted in form of a Z scheme) Both processes are mediated by the action of two RCs (which essentially act in series): These are called PS I and PS II PS I: generates a strong reductant capable of reducing NADP+ PS II: generates a strong oxidant capable of oxidizing water to O2 1 Simple Z Scheme for photosynthesis in plants and cyanobacteria DCMU is a herbicide which interrupts electron flow from PS II to cyt f 2 1 Another Z Scheme 3 4 2 The Thylakoid membrane and its components Stroma Thylakoid lumen 5 Q cycle Q QH2 6 3 Plastocyanin (PC) PC is a mobile electron carrier transferring electrons from cytochrome b6f complex to PS I PC is a blue copper protein 7 Structure of Plastocyanin 8 4 Environment of the Cu(II) in blue copper proteins is highly strained (entatic state) 9 EPR (Electron paramagnetic resonance) spectroscopy Splitting in external magnetic fields 10 5 EPR spectroscopy of Cu(II) proteins The unpaired electron in Cu(II) is delocalized over the thiolate sulfur of cysteine in blue copper centres (this is why the hyperfine splitting in the protein is less than in a normal Cu complex) 11 Arrangement of cofactors in the RC subunits of PS II 12 6 13 14 7 15 The Oxygenevolving complex (OEC) 16 8 17 18 9 Previously proposed structure of the Mn4 cluster in OEC New structures 2011 (1.9 Å res.) 19 2009 Ligand environment of the OEC (1.9 Å structure) Kawakami, K. et al. (2011) J. Photochem. Photobiol. B: Biol. 104, 9-18. 20 10 Kawakami, K. et al. (2011) J. Photochem. Photobiol. B: Biol. 104, 9-18. 21 Revised mechanism of OEC Siegbahn, P.E.M. (2009) Acc. Chem. Res. 42, 1871-1880. 22 11 Model complexes 23 24 12 A working model compound 25 Dark reactions (Calvin cycle) 26 13