Chemiosmotic coupling

Complex IV Cytochrome c Oxidase The Thermodynamic View of Chemiosmotic Coupling ATP Synthase... 

Mohn WW, JM Tiedje (1991) Evidence for chemiosmotic coupling of reductive dechlorination and ATP synthesis in Desulfomonile tiecljei. Arch Microbiol 157 1-6. 

Mitchell, P. (1966). Chemiosmotic Coupling in Oxidative and Photosynthetic Phosphorylation. Glynn Research, Bodmin, Cornwall, U.K. 

Chemiosmotic Coupling Allows Nonintegral Stoichiometries of 02 Consumption and ATP Synthesis... 

Mitchell, P. (1968) Chemiosmotic Coupling and Energy Transduction, Glynn Res., Bodmin., Cornwall, England... 

The chemiosmotic coupling hypothesis, proposed by P. Mitchell, is the most attractive explanation, and many experimental observations now support this idea. Simply stated, Mitchell s hypothesis suggests that electron transfer is accompanied by transport of protons across the membrane. 

Chemiosmotic coupling. The coupling of ATP synthesis to an electrochemical potential gradient across a membrane. 

Mitchell, P. Moyle, J. (1985). The role of ubiquinone and plastoquinone in chemiosmotic coupling between electron transfer and proton translocation in coenzyme Q. In (Lenaz, G., ed.) pp. 145-163, Wiley, Chichester. 

According to the chemiosmotic coupling hypothesis, ATP synthesis decreases the proton electrochemical gradient and hence stimulates the respiratory chain to pump more protons across the mitochondrial inner membrane and maintain the gradient. However, electron supply to the respiratory chain also affects respiration and ATP synthesis. For example, calcium stimulates mitochondrial matrix dehydrogenase, and increases the electron supply to the respiratory chain and hence the rate of respiration and ATP synthesis. 

ATP formation coupled to electron flow in mitochondria is usually called oxidative phosphorylation. Because electron flow involves both reduction and oxidation, more appropriate names are respiratory phosphorylation and respiratory-chain phosphorylation, terminology that is also more consistent with photophosphorylation for ATP formation in photosynthesis. As with photophosphorylation, the mechanism of oxidative phosphorylation is not yet fully understood in molecular terms. Processes like phosphorylation accompanying electron flow are intimately connected with membrane structure, so they are much more difficult to study than are the biochemical reactions taking place in solution. A chemiosmotic coupling mechanism between electron flow and ATP formation in mitochondria is generally accepted, and we will discuss some of its characteristics next. 

P. Mitchell. 1976. Vectorial chemistry and the molecular mechanics of chemiosmotic coupling Power transmission by proticity Biochem. Soc. Trans. 4 399-430. (PubMed)... 

Fig. 1.3. A scheme of oxidative phosphorylation according to the chemiosmotic coupling hypothesis.

The inconsistency between experiment and prediction must lead to the rejection of the model used to describe the system. In the case of oxidative phosphorylation this has led to a refined model, in which the chemiosmotic coupling is visualized as taking place within units of one (or a few) respiratory chain(s) plus ATP synthase, while the pumped protons have only limited access to the bulk phase inside and/or outside the mitochondrion [42]. This more refined model can again be tested by deriving from it flux-force relations according to the MNET approach. A discussion of the refined model can be found in Ref. 43. 

The evidence which has been put forward to favour such localized schemes is largely thermodynamic and will be summarized below. It must be borne in mind, however, that any localized circuit must be consistent, not only with the deviations in the thermodynamic relationships which led to the particular model, but also with the wealth of information available about chemiosmotic coupling in general. Some of these have been discussed above and will now be restated ... 

Nicholls, D.G., Cannon, B., Grav, H.J. and Lindberg, O. (1974) In Dynamics of Energy-Transducing Membranes (Emster, L., Estabrook, R.W. and Slater, E.C., eds.) pp. 529-537, Elsevier, Amsterdam. Mitchell, P. (1966) Chemiosmotic Coupling in Oxidative and Photosynthetic Phosphorylation. Glynn Res. Ltd., Bodmin, Cornwall, England. 

The anisotropic organization of electron carriers across the membrane accounts for the vectorial transport of protons from the inside to the outside of the membrane, which occurs with the passage of electrons. The coupling of this proton gradient to a proton-translocating ATP synthase (also known as ATP synthetase) accounts for the chemiosmotic coupling in oxidative phosphorylation. 

In 1961, Peter Mitchell, a British biochemist, proposed a mechanism by which the free energy generated during electron transport drives ATP synthesis. Now widely accepted, Mitchell s model, referred to as the chemiosmotic coupling theory (Figure 10.11), has the following principal features ... 

Mitchell, P., Chemiosmotic coupling in oxidative and photosynthetic phosphorylation, Biol. Rev. Camb. Philos. Soc., 1966, 41, 445-502. WiKSTEOM, M.K., Proton pump coupled to cytochrome c oxidase in mitochondria. Nature, 1977, 266, 271-273. 

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