Proton influx

Proton influx through the F0 base-piece of the ATP-synthase in the inner membrane drives the formation of ATP by causing the release of bound ATP from the catalytic site on the F, head-piece of the enzyme. 

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. 17.26electron-transfer reactions (or,... 

Fig. 21.4. Binding change mechanism for ATP synthesis. The three ap subunit pairs of the ATP synthase headpiece have binding sites that can exist in three different conformations, depending on the position of the 7 stalk subunit. Step 1 When ADP + Pi bind to an open site and the proton influx rotates the 7 spindle (represented by the arrow), the conformation of the subunits change and ATP is released from one site. (ATP dissociation is, thus, the energy-requiring step). Bound ADP and Pi combine to form ATP at another site. Step 2 As the ADP + Pi bind to the new open site, and the 7 shaft rotates, the conformations of the sites change again, and ATP is released. ADP and Pi combine to form another ATP.

A Endocytosis B Proton Influx C Osmosis D Lysis E Release... 

Washed chloroplast thylakoids and isolated CF have low ATPase activities. Illumination of thylakoids in the presence of dithiothreitol allows sustained ATP hydrolysis in the dark, ATP hydrolysis is stimulated by uncouplers, is sensitive to phosphorylation inhibitors and is coupled to proton influx. The ATPase activity of soluble CF is also enhanced dramatically by treatment of the enzyme with high concentrations of dithiothreitol. 

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