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The cytochrome ''b''6''f'' complex (plastoquinol—plastocyanin reductase; ) is an enzyme found in the thylakoid membrane in chloroplasts of plants, cyanobacteria, and green algae, catalyzing the transfer of electrons from plastoquinol to plastocyanin. The reaction is analogous to the reaction catalyzed by cytochrome bc1 (Complex III) of the mitochondrial electron transport chain. For photosynthesis, the cytochrome b6f complex transfers electrons between the two reaction complexes from Photosystem II to Photosystem I, whereby introducing protons into the thylakoid space to generate an electrochemical gradient that stores energy for ATP synthesis. == Enzyme structure == The cytochrome b6f complex is a dimer, with each monomer composed of eight subunits. These consist of four large subunits: a 32 kDa cytochrome f with a c-type cytochrome, a 25 kDa cytochrome b6 with a low- and high-potential heme group, a 19 kDa Rieske iron-sulfur protein containing a () cluster, and a 17 kDa subunit IV; along with four small subunits (3-4 kDa): PetG, PetL, PetM, and PetN.〔 The total molecular weight is 217 kDa. The crystal structure of cytochrome b6f complexes from ''Chlamydomonas reinhardtii'', ''Mastigocladus laminosus'', and ''Nostoc'' sp. PCC 7120 have been determined.〔 The core of the complex is structurally similar to cytochrome bc1 core. Cytochrome b6 and subunit IV are homologous to cytochrome b and the Rieske iron-sulfur proteins of the two complexes are homologous. However, cytochrome f and cytochrome c1 are not homologous. Cytochrome b6f contains seven prosthetic groups. Four are found in both cytochrome b6f and bc1: the c-type heme of cytochrome c1 and f, the two b-type hemes (bp and bn) in bc1 and b6f, and the () cluster of the Rieske protein. Three unique prosthetic groups are found in cytochrome b6f: chlorophyll a, β-carotene, and heme cn (also known as heme x).〔 The inter-monomer space within the core of the cytochrome b6f complex dimer is occupied by lipids,〔 which provides directionality to heme-heme electron transfer through modulation of the intra-protein dielectric environment. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cytochrome b6f complex」の詳細全文を読む スポンサード リンク
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