The cytochrome b₆f complex (plastoquinol—plastocyanin reductase; EC 1.10.99.1 (http://www.expasy.org/cgi-bin/get-enzyme-entry?1.10.99.1)) of chloroplasts and cyanobacteria transfers electrons between the two reaction center complexes of oxygenic photosynthetic membranes, photosystem I and photosystem II, and participates in formation of the transmembrane electrochemical proton gradient by also transferring protons from the stromal to the internal lumen compartment. It is minimally composed of four subunits: cytochrome b₆, carrying a low- and a high-potential heme groups (b_L and b_H); cytochrome f with one covalently bound heme c; Rieske iron-sulfur protein (ISP) containing a single [Fe₂S₂] cluster; and subunit IV (17 kDa protein). In its structure and functions, the cytochrome b₆f complex bears extensive analogy to the cytochrome bc₁ complex of mitochondria and photosynthetic purple bacteria. However, there are important differences between the two complexes: EC numbers (Enzyme Commission numbers) are a numerical classification scheme for enzymes, based on the chemical reactions they catalyze. ... Chloroplasts stuff my mom raped are organelles found in plant cells and eukaryotic algae which conduct photosynthesis. ... Cyanobacteria (Greek: cyanos = blue) are a phylum of aquatic bacteria that obtain their energy through photosynthesis. ... In the process of photosynthesis, light is absorbed by a photosystem (ancient Greek: phos = light and systema = assembly) to begin an energy-producing reaction. ... An ion gradient is a concentration gradient of ions, it can be called an electrochemical potential gradient of ions across membranes. ... CoQ Cytochrome c reductase The Coenzyme Q - cytochrome c reductase complex, sometimes called the cytochrome bc1 complex, and at other times Complex III, is the third complex in the electron transfer chain (PDB 1KYO, EC 1. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... Purple bacteria are proteobacteria that are phototrophic, i. ...

• The single-polypeptide cytochrome b in the cytochrome bc₁ complex corresponds to cytochrome b₆ and subunit IV in the cytochrome b₆f complex
• Cytochrome f and cytochrome c₁ are not homologous
• The cytochrome b₆f complex contains additional chromophores, chlorophyll a, β-carotene and atypical heme c_i (heme x), the latter being linked by a single thioether bond to cytochrome b₆

The cytochrome b₆f complex is responsible for "non-cyclic" (1) and "cyclic" (2) electron transfer between two mobile redox carriers, plastoquinol (QH₂) and plastocyanin: Chlorophyll is a green photosynthetic pigment found in plants, algae, and cyanobacteria. ... Carotene is a terpene, an orange photosynthetic pigment, important for photosynthesis. ... Plastoquinone Plastoquinone, often abbreviated pq, is a molecule used in the electron transport chain in the light-dependent reactions of photosynthesis. ...

Electron transfer is coupled with the translocation of protons across the membrane, thus generating proton-motive force in the form of an electrochemical proton potential which can drive ATP synthesis. The crystal structure of cytochrome b₆f complexes from Chlamydomonas reinhardtii and Mastigocladus laminosus have been determined.

References

• Cramer, W.A., Martinez, S.E., Furbacher, P., Huang, D. and Smith, J.L. (1994). The cytochrome b₆f complex. Curr. Opin. Struct. Biol., 4, 536–544.
• Cramer, W.A., Zhang, H., Yan, J., Kurisu, G. and Smith, J.L. (2004). Evolution of photosynthesis: time-independent structure of the cytochrome b₆f complex. Biochemistry, 43, 5921–5929.
• Schoepp, B., Chabaud, E., Breyton, C., Verméglio, A. and Popot, J.-L. (2000). On the spatial organization of hemes and chlorophyll in cytochrome b₆f. A linear and circular dichroism study. J. Biol. Chem., 275, 5275–5283.
• Stroebel, D., Choquet, Y., Popot, J.-L. and Picot, D. (2003). An atypical haem in the cytochrome b₆f complex. Nature, 426, 413–418.

External links

• 1Q90 (http://www.rcsb.org/pdb/cgi/explore.cgi?pdbId=1Q90) - PDB structure of cytochrome b₆f complex from Chlamydomonas reinhardtii
• 1VF5 (http://www.rcsb.org/pdb/cgi/explore.cgi?pdbId=1VF5) - PDB structure of cytochrome b₆f complex from Mastigocladus laminosus
• Cytochrome b₆f page (http://www.biology.purdue.edu/people/faculty/cramer/cramer/html/cytbf.html) @ Purdue University, USA