Ubiquinone:cytochrome composition

Darzon A, Vandenberg CA, Schonfeld M, Ellisman MH, Spitzer NC and Montal M (1980) Reassembly of protein-lipid complexes into large bilayer vesicles perspectives for membrane reconstitution, Proc.Natl.Acad.Sci USA 77, 239-243. Dutton PL, Mueller P, O Keefe DP, Packham NK, Prince RC and Tiede DM (1982) Electrogenic reactions of the photochemical reaction center and the ubiquinone-cytochrome b/c oxidoreductase, Curr.Top.Membr.Transp. 16, 323-343. Feher G and Okamura MY (1978) Chemical composition and properties of reaction centers. In Clayton RK and Sistrom WR, ed. The photosynthetic bacteria, pp. 349-386. New York Plenum Press. 

The branch point between the Aox and the cytochrome respiratory chain arises at the ubiquinone pool. These terminal oxidases can be identified by using respiratory inhibitors and are divided as different groups according to the sensitivities or resistances to the inhibitors. Alternative respiration is activated by stress stimuli factors that constrict the electron flow through the cytochrome pathway [137]. However, the roles and the compositions of these pathways are... 

The respiratory chain. Boxes indicate the composition of complexes I to IV. Electron flow is shown by arows. Sites of action of some inhibitors are labeled 1, 2 and 3, and indicated by horizontal bars. Sites 2 and 3 are also coupled with ATP synthesis, i.e. according to the chemiosmotic theory, each of these stages of electron transfer (from cytochrome b to cytochrome c, and from cytochrome to oxygen) provides enough energy to generate a proton gradient for the synthesis of one molecule of ATP. The first site of ATP synthesis may not be identical with inhibition site 1 as shown here, but it is known to exist on the ubiquinone side (rather than the substrate side) of complex I. 

It should be noted that this constitutes a more specific version of the large general diagram in Section 4. Ubiquinone and cytochrome c are represented as auxiliary substrates the complexes within the frames are the true enzymes of the respiratory chain. Their composition, particularly with regard to prosthetic groups, is not yet fully understood. It is even possible that additional complexes may be involved. Many current controversies will hopefully be decided experimentally in the near future. 

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