ATP from ADP

Complex V catalyzes the synthesis of ATP from ADP and Pj utilizing the energy of the proton motive force across the inner membrane (Senior, 1988,1990). 

Spanning the membrane are ATP synthase complexes that use the potential energy of the proton gradient to synthesize ATP from ADP and P,. In this way, oxidation is closely coupled to phosphorylation to meet the energy needs of the cell. 

Creatine phosphate prevents the rapid depletion of ATP by providing a readily available high-energy phosphate that can be used to regenerate ATP from ADP. 

The synthesis of ATP from ADP and phosphoric acid is nonspontaneous. Consequently, ATP synthesis must be coupied to some more spontaneous reaction. Example 14-10 describes one of these reactions. 

Acetate kinase is phosphorylated by acetyl phosphate and it has been shown that the phosphoenzyme can synthesise ATP from ADP, and acetyl phosphate from acetate. The mode of decomposition of carbamyl phosphate in aqueous solution is pH dependent and can proceed with either the production of ammonia and carbon dioxide (equation 1), or cyanate (equation 2). No cyanate could be detected during the hydrolysis... 

A well-known example of active transport is the sodium-potassium pump that maintains the imbalance of Na and ions across cytoplasmic membranes. Flere, the movement of ions is coupled to the hydrolysis of ATP to ADP and phosphate by the ATPase enzyme, liberating three Na+ out of the cell and pumping in two K [21-23]. Bacteria, mitochondria, and chloroplasts have a similar ion-driven uptake mechanism, but it works in reverse. Instead of ATP hydrolysis driving ion transport, H gradients across the membranes generate the synthesis of ATP from ADP and phosphate [24-27]. 

During a search for high-energy phosphates, Ponnamperuma was able to synthesize adenosine triphosphate (ATP) from ADP, AMP or adenosine from ethyl metaphosphate in dilute aqueous solution under the influence of UV light. The role of the UV irradiation is unclear, as the phosphate itself is a high-energy species (Ponnamperuma et al., 1963). 

Thus, in one cycle, eight hydrogen atoms (H+ + e ) are transferred to hydrogen-transmitting coenzymes and later oxidized to water in the respiratory chain. This process is linked to oxidative phosphorylation, i.e., the synthesis of ATP from ADP and inorganic phosphate. 

In a chemical model for oxidative phosphorylation77 the anaerobic oxidation of iV-benzyl 1,4-dihydronicotinamide by a pyridine solution of haemin was accompanied by the synthesis of ATP from ADP and inorganic phosphate. In support of an alternative chemical model involving sulphenyl phosphates as the reactive species,78 lipophilic thioureas have been shown to inhibit mitochondrial oxidative phos-... 

ATP synthesis is the final step in the conservation of energy via chemios-mosis. This step is catalyzed by FiFo ATP synthase, a multisubunit enzyme complex found exclusively in cytoplasmic membranes of bacteria (Senior 1988). It uses the chemiosmotic energy (ApH) generated from membrane ET to synthesize ATP from ADP and Pi. The most investigated bacterial... 

The net result of Equations (7.91) and (7.92) is the same as the sum of Equation (7.90), for which AG = 29,300 Jmol and the formation of ATP from ADP, the reverse of Equation (7.90) for which AG = +29,300 Jmol Thus, the value of AG for the overall reaction is 0, which means that reactants and products exist at comparable concentrations, with ATP available to drive other reactions. 

These enzymes, together with the proteins that generate ATP from ADP and P, (phosphate), constitute 30-40% of the total protein of the inner mitochondrial membrane. 

The major role of electron transfer is the generation of ATP from ADP and P, (oxidative phosphorylation). Since the... 

A fuel is a compound that leads to generation of ATP from ADP and P, (Figure 13.17). The fuels used by muscle differ according to fibre, the type of activity and the conditions under which the activity takes place. For example, in athletics, the fuel used varies according to the particular event, from the 100 m sprint to the marathon. 

Nucleosides are also encountered in the structures of adenosine triphosphate (ATP) and coenzyme A (HSCoA). ATP provides nature with its currency unit for energy. Hydrolysis of ATP to adenosine diphosphate (ADP) liberates energy, which can be coupled to energy-requiring processes in biochemistry, and synthesis of ATP from ADP can be coupled to energy-releasing processes (see Box 7.25). 

In both cases, the mixed anhydride is used to synthesize ATP from ADP. Hydrolysis of the anhydride liberates more energy than the hydrolysis of ATP to ADP and, therefore, can be linked to the enzymic synthesis of ATP from ADP. This may be shown mechanistically as a hydroxyl group on ADP acting as nucleophile towards the mixed anhydride, and in each case a new phosphoric anhydride is formed. In the case of succinyl phosphate, it turns out that GDP rather than ADP attacks the acyl phosphate, and ATP production is a later step (see Section 15.3). These are enzymic reactions therefore, the reaction and the nature of the product are closely controlled. We need not concern ourselves why attack should be on the P=0 rather than on the C=0. 

The total oxidation of an organic componnd nsing molecnlar oxygen as the electron acceptor has the potential to yield a very large amonnt of energy, sufficient for the synthesis of several molecnles of ATP from ADP, if there could be one efficiently coupled oxidation process. It is quite unrealistic... 

Most compounds oxidized by the electron transport chain donate hydrogen to NAD+, and then NADH is reoxidized in a reaction coupled to reduction of a flavoprotein. During this transformation, sufficient energy is released to enable synthesis of ATP from ADP. The reduced flavoprotein is reoxidized via reduction of coenzyme Q subsequent redox reactions then involve cytochromes and electron transfer processes rather than hydrogen transfer. In two of these cytochrome redox reactions, there is sufficient energy release to allow ATP synthesis. In... 

The product succinyl-CoA is able to participate in ATP synthesis as an example of substrate-level phosphorylation - we met some other examples in the glycolytic pathway. Essentially, hydrolysis of succinyl-CoA liberates snfficient energy that it can be coupled to the synthesis of ATP from ADP. However, guanosine triphosphate (GTP) is the... 

The inner membrane itself plays an important part in oxidative phosphorylation. As it is impermeable to protons, the respiratory chain—which pumps protons from the matrix into the intermembrane space via complexes 1, 111, and IV—establishes a proton gradient across the inner membrane, in which the chemical energy released during NADH oxidation is conserved (see p. 126). ATP synthase then uses the energy stored in the gradient to form ATP from ADP and inorganic phosphate. Several of the transport systems are also dependent on the H"" gradient. 

Respiration is a ubiquitous and complex oxidative mechanism that conserves energy, liberated by the catabolism of molecules such as carbohydrates, through the production of ATP from ADP and orthophosphate. Several component reaction sequences can be identified. 

Water is not just the solvent in which the chemical reactions of living cells occur it is very often a direct participant in those reactions. The formation of ATP from ADP and inorganic phosphate is an example of a condensation reaction in which the elements of water are eliminated (Fig. 2-22a). The reverse of this reaction— cleavage accompanied by the addition of the elements of water—is a hydrolysis reaction. Hydrolysis reactions are also responsible for the enzymatic depolymerization of proteins, carbohydrates, and nucleic acids. Hydrolysis reactions, catalyzed by enzymes called... 

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