Adhesion Molecules-28

Advances and Experimental-3

Aging-9

Agricultural Biotechnology-37

Angiogenesis-29

Antisense-4

Apoptosis-49

Atherosclerosis-12

Autoimmunity-69

Bacterial Virulence-18

Bioinformatics-13

BioMaterials-18

Biosurfactants-1

Biotechnology-100

Cancer Genetics-25

Cancer Metastasis-19

Cell Biology-16

Cell Cycle-34

Cell Metabolism-327

Channels and Transporters-79

Chaperones-11

Circadian Rhythms-13

Coagulation-14

Cytokines/Growth Factors-52

Development-223

DNA-56

DNA Surveillance and Repair-42

Drug Design-17

Endocrine-66

Evolution-33

Extracellular Matrix-30

Gastroenterology-52

Gene Expression-178

Gene Therapy-53

Heart-61

Heat Shock Proteins-19

Hematology-11

Immunology-93

Infectious Disease-71

Ischemia-Reperfusion-33

Leptin and Leptin Antagonists-1

Medical-22

MHC-17

Mitochondria-17

Molecular Biology-20

Molecular Complexes and Signaling-1

Nanomedicine-30

Neurodegenerative Disease-72

Neuropharmacology-112

Neuroscience-38

Nucleus-15

Oncogenes-8

Oncology-87

Parasitic Disease-12

Pharmacogenomics-14

Prebiotic Evolution-6

Protein-12

Reproductive Biology-60

RNA-152

Signal Transduction-186

Stem Cells-80

Surgery-37

T-Cell Activation-12

Tissue Engineering-116

Transplant-51

Vaccines-82

Viruses-85

Chapter category: Agricultural Biotechnology

Photosystem II: Composition and Structure

Chapter authors:
Aspasia Spyridaki, Emmanuel Psylinakis and Demetrios F. Ghanotakis

Photosystem II (PSII) is a light driven, water-plastoquinone oxidoreductase which catalyses the most thermodynamically demanding reaction in biology.1 This highly endergonic reaction splits water into molecular oxygen, protons and electrons, thereby sustaining an aerobic atmosphere on earth and providing the reducing equivalents necessary to fix carbon dioxide to organic molecules, creating biomass, food and fuel. PSII is a multisubunit pigment-protein complex embedded in the thylakoid membranes of higher plants, algae and cyanobacteria. Its unique properties require an elaborate arrangement of integral membrane proteins, specifically bound pigment moieties, extrinsic proteins and inorganic cofactors. Light energy is absorbed by light harvesting complexes that contain most of the pigments associated with PSII. Excitation energy is transferred from this antenna to the “core” of the PSII complex, where the primary photochemistry takes place. This photochemical part of PSII contains the ultra-fast and very efficient light-induced charge separation and stabilization steps that occur vectorially across the membrane. Finally, the photochemical reactions result in the accumulation of oxidizing equivalents in the oxygen-evolving complex (OEC); four oxidizing equivalents are used to convert two molecules of water into oxygen. The photochemical and enzymatic reactions catalyzed by PSII are strictly conserved among all oxygenic photosynthetic organisms including cyanobacteria, eukaryotic algae and higher plants, while quite diverse pigment-protein complexes have developed for light-harvesting antenna systems associated with PSII.2,3 These antenna systems, though similar in function, differ in their structures, with those of higher plants and green algae (LHCP) being located in the thylakoid membrane while those of most classes of cyanobacteria (phycobilisomes) are bound extrinsically to the stromal surface of PSII. With regard to protein structure, the PSII complex differs mostly in peripheral subunits between cyanobacteria and higher plants but shares the core parts in common.4

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