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<a target="_blank" rel="noopener" href="https://fatcat.wiki/container/4qyryvw5mvde5nt6xjruewxve4" style="color: black;">Biochemistry</a>
Structures of the cytochrome b 6 f complex obtained from the thermophilic cyanobacterium Mastigocladus laminosus and the green alga Chlamydomonas reinhardtii, whose appearance in evolution is separated by 10 9 years, are almost identical. Two monomers with a molecular weight of 110 000, containing eight subunits and seven natural prosthetic groups, are separated by a large lipid-containing "quinone exchange cavity". A unique heme, heme x, that is five-coordinated and high-spin, with no strong<span class="external-identifiers"> <a target="_blank" rel="external noopener noreferrer" href="https://doi.org/10.1021/bi049444o">doi:10.1021/bi049444o</a> <a target="_blank" rel="external noopener" href="https://www.ncbi.nlm.nih.gov/pubmed/15147175">pmid:15147175</a> <a target="_blank" rel="external noopener" href="https://fatcat.wiki/release/fkjwpz4z4rbkpjbjtues6glepq">fatcat:fkjwpz4z4rbkpjbjtues6glepq</a> </span>
more »... eld ligand, occupies a position close to intramembrane heme b n . This position is filled by the n-side bound quinone, Q n , in the cytochrome bc 1 complex of the mitochondrial respiratory chain. The structure and position of heme x suggest that it could function in ferredoxin-dependent cyclic electron transport as well as being an intermediate in a quinone cycle mechanism for electron and proton transfer. The significant differences between the cyanobacterial and algal structures are as follows. (i) On the n-side, a plastoquinone molecule is present in the quinone exchange cavity in the cyanobacterial complex, and a sulfolipid is bound in the algal complex at a position corresponding to a synthetic DOPC lipid molecule in the cyanobacterial complex. (ii) On the p-side, in both complexes a quinone analogue inhibitor, TDS, passes through a portal that separates the large cavity from a niche containing the Fe 2 S 2 cluster. However, in the cyanobacterial complex, TDS is in an orientation that is the opposite of its position in the algal structure and bc 1 complexes, so its headgroup in the M. laminosus structure is 20 Å from the Fe 2 S 2 cluster. † The studies reported in this review were supported by NIH Grant GMS-38323 (W.A.C.) and a fellowship from The Japanese Ministry of Education (G.K.).
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