Transmembrane proton gradient

Recent studies by Crompton et al. have shown that oxidant stress may open a Ca-sensitive, non-selective pore in the inner mitochondrial membrane that is blocked by cyclosporin A (Crompton, 1990 Crompton and Costi, 1990). This pore opening results in massive mitochondrial swelling, dissipation of the transmembrane proton gradient and disruption of mitochondrial energy production (Crompton et al., 1992). Since mitochondria may play a role as a slow, high-capacity cytosolic calcium buffer (Isenberg et al., 1993), disruption of mitochondrial function may also contribute to calcium overload and cell injury. 

It shows a section through a bacterial cell (only one corner of the cell is shown). ATP synthase links the discharge of the transmembrane proton gradient to the formation of ATP, A simple mechanism (hydrogen cycling) B. a mechanism in which the membrane-bound electron-transfer proteins are proton pumps. 

Figure 1 Facing page) (A) Mechanism of remote loading of doxorubicin by transmembrane ammonium sulfate gradient. (B) Collapse of transmembrane ammonium ion gradient in SSL by nonactine induces doxorubicin release. (C) Collapse of transmembrane proton gradient in SSL by nigericin induces collapse of transmembrane ammonium ion gradient followed by release of DOX. Abbreviations. DOX, doxorubicin SSL, sterically stabilized liposome.

Collapse of Liposomal Transmembrane Ammonium Ion and Proton Gradient and Release of Encapsulated DOX by lonophores... 

The cytochrome b(6)f complex mediates electron transfer between the PSI and PSII reaction centers by oxidizing hpophUic plastoquinol (PQH2) (see Figure 7.24) and reducing the enzymes plastocyanin or cytochrome Ce. The electronic connection also generates a transmembrane electrochemical proton gradient that can support adenosine triphosphate (ATP) synthesis instead of electron transport. 

In chemical terms the photoinduced electron transfer results in transfer of an electron across the photosynthetic membrane in a complex sequence that involves several donor-acceptor molecules. Finally, a quinone acceptor is reduced to a semiquinone and subsequently to a hydroquinone. This process is accompanied by the uptake of two protons from the cytoplasma. The hydroquinone then migrates to a cytochrome be complex, a proton pump, where the hydroquinone is reoxidized and a proton gradient is established via transmembrane proton translocation. Finally, an ATP synthase utilizes the proton gradient to generate chemical energy. Due to the function of tetrapyrrole-based pigments as electron donors and quinones as electron acceptors, most biomimetic systems utilize some... 

A second membrane transport system essential to oxidative phosphorylation is the phosphate translocase, which promotes symport of one H2PO4 and one H+ into the matrix. This transport process, too, is favored by the transmembrane proton gradient (Fig. 19-26). Notice that the process requires movement of one proton from the P to the N side of the inner membrane, consuming some of the energy of electron transfer. A complex of the ATP synthase and both translocases, the ATP synthasome, can be isolated from... 

N2 under anaerobic conditions, a process called denitrification (Fig. 22-1). These soil bacteria use N03 rather than 02 as the ultimate electron acceptor in a series of reactions that (like oxidative phosphorylation) generates a transmembrane proton gradient, which is used to synthesize ATP. 

Keyes, S.R. Rudnick, G. (1992). Coupling of transmembrane proton gradients to platelet serotonin transport. J. Biol. Chem. 257,1172-1176. 

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