Electron transfer proton pumps driven

Because the four protons produced in this reaction are released into the thylakoid lumen, the oxygen-evolving complex acts as a proton pump, driven by electron transfer. The sum of Equations 19-12 through 19-15 is... 

Chemiosmotic theory readily explains the dependence of electron transfer on ATP synthesis in mitochondria. When the flow of protons into the matrix through the proton channel of ATP synthase is blocked (with oligomycin, for example), no path exists for the return of protons to the matrix, and the continued extrusion of protons driven by the activity of the respiratory chain generates a large proton gradient. The proton-motive force builds up until the cost (free energy) of pumping... 

Cells drive active transport in a variety of ways. The plasma-membrane Na+-K+ pump of animal cells (a) and the plasma-membrane H+ pump of anaerobic bacteria (b) are driven by the hydrolysis of ATP. Eukaryotic cells couple the uptake of neutral amino acids to the inward flow of Na+ (c). Uptake of /3-gal actosidcs by some bacteria is coupled to inward flow of protons (d). Electron-transfer reactions drive proton extrusion from mitochondria and aerobic bacteria (e). In halophilic bacteria, bacteriorhodopsin uses the energy of sunlight to pump protons (/). E. coli and some other bacteria phosphorylate glucose as it moves into the cell and thus couple the transport to hydrolysis of phosphoenolpyruvate (g). 

Active transport of a solute against a concentration gradient also can be driven by a flow of an ion down its concentration gradient. Table 17.6 lists some of the active-transport systems that operate in this way. In some cases, the ion moves across the membrane in the opposite direction to the primary substrate (antiport) in others, the two species move in the same direction (symport). Many eukaryotic cells take up neutral amino acids by coupling this uptake to the inward movement of Na+ (see fig. 17.26c). As we discussed previously, Na+ influx is downhill thermodynamically because the Na+-K+ pump keeps the intracellular concentration of Na+ lower than the extracellular concentration and sets up a favorable electric potential difference across the membrane. Another example is the /3-galactosidc transport system of E. coli, which couples uptake of lactose to the inward flow of protons (see fig. 17.26Proton influx is downhill because electron-transfer reactions (or,... 

Oxidative phosphorylation is the culmination of a series of energy transformations that are called cellular respiration or simply respiration in their entirety. First, carbon fuels are oxidized in the citric acid cycle to yield electrons with high transfer potential. Then, this electron-motive force is converted into a proton-motive force and, finally, the proton-motive force is converted into phosphoryl transfer potential. The conversion of electron-motive force into proton-motive force is carried out by three electron-driven proton pumps—NADH-Q oxidoreductase, Q-cytochrome c oxidoreductase, and... 

Another area of increasing emphasis is the elucidation of chemical bonding rearrangements either initiated by or accompanying ET for example, coupled proton- (or other ion ) electron transfer cpet) [20, 22] and dissociative ET [80]. Such a focus, of course, lies at the heart of much current research in solar-energy conversion. An especially exciting recent development is the construction of a functioning biomimetic photon-driven proton pump [81]. 

Proton-coupled electron transfer (PCET) reactions play a fundamental role in the respiratory chain and in photosynthesis. In both membrane-bound systems, an electrochemical gradient is built up across the lipid bilayer by separating protons from electrons the resulting chemiosmotic proton potential serves to fuel a proton-driven pump synthesising the universal biological energy equivalent ATP (adenosine triphosphate). In addition to the relevance of PCET in these energy conversions, the coupled transfer of electrons and protons is an... 

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