The Z-Scheme Diagram of Photosynthesis
The Z-Scheme Diagram of Photosynthesis
The Electron Transport Pathway from Water (H2O) to NADP + (the Nicotinamide Adenine Dinucleotide Phosphate, oxidized form). [This diagram was developed by Wilbert Veit and Govindjee, and can be also found at "www.molecadv.com"]Abbreviations used are (from left to the right of the diagram): Mn for a manganese complex containing 4 Mn atoms, bound to Photosystem II (PSII) reaction center; Tyr for a particular tyrosine in PSII; O2 for oxygen; H+ for protons; P680 for the reaction center chlorophyll (Chl) in PSII: it is the primary electron donor of PSII; Excited P680 for P680* that has the energy of the photon of light; Pheo for pheophytin molecule (the primary electron acceptor of PSII; it is like a chlorophyll a molecule where magnesium (in its center) has been replaced by two "H"s); Q A for a plastoquinone molecule tightly bound to PSII; QB for another plastoquinone molecule that is loosely bound to PSII; FeS for Rieske Iron Sulfur protein; Cyt. f for Cytochrome f; Cytb6(L and H) for Cytochrome b6 (of Low and High Energy); PC for copper protein plastocyanin; P700 for the reaction center chlorophyll of PSI; it is the primary electron donor of PSI;Excited P700 for P700* that has the energy of the photon of light; Ao for a special chlorophyll a molecule (primary electron acceptor of PSI); A 1 for a phylloquinone (Vitamin K) molecule; FX, FA, and FB are three separate Iron Sulfur Centers; FD for ferredoxin; and FNR for Ferredoxin-NADP-oxido-Reductase(FNR).Three major protein complexes are involved in running the "Z" scheme: (1) Photosystem II; (2) Cytochrome bf complex (containing Cytb6; FeS; and Cytf ) and (3) Photosystem I. ATP is synthesized by ATP synthase located in the chloroplast membranes utilizing the protons released from water and reduced plastoquinone. For a full description of the entire process, see "Photosynthetic Process" by J.Whitmarsh and Govindjee.
