Adenosine diphosphate, hydrolysis

Nicotinamide is incorporated into NAD and nicotinamide is the primary ckculating form of the vitamin. NAD has two degradative routes by pyrophosphatase to form AMP and nicotinamide mononucleotide and by hydrolysis to yield nicotinamide adenosine diphosphate ribose. 

Phosphate condensation reactions play an essential role in metabolism. Recall from Section 14.6 that the conversion of adenosine diphosphate (ADP) to adenosine triphosphate (ATP) requires an input of free energy ADP -I-H3 PO4 ATP +H2O AG° — +30.6kJ As also described in that section, ATP serves as a major biochemical energy source, releasing energy in the reverse, hydrolysis, reaction. The ease of interchanging O—H and O—P bonds probably accounts for the fact that nature chose a phosphate condensation/hydrolysis reaction for energy storage and transport. 

Similarly, specific catalysts called enzymes are important factors in determining what reactions occur at an appreciable rate in biological systems. For example, adenosine triphosphate is thermodynamically unstable in aqueous solution with respect to hydrolysis to adenosine diphosphate and inorganic phosphate. Yet this reaction proceeds very slowly in the absence of the specific enzyme adenosine triphosphatase. This combination of thermodynamic control of direction and enzyme control of rate makes possible the finely balanced system that is a hving cell. 

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). 

Beyond the effect of magnesium ion concentration on the equilibrium hydrolysis of adenosine triphosphate to adenosine diphosphate , there is ample evidence that MgATP is generally the most widespread substrate in kinase-type phosphotransferase reactions as well as other ATP-dependent processes. The extent to which MgATP is formed in solution depends on the free (or uncomplexed) magnesium ion concentration, as shown by the following equilibrium constant ... 

The hydrolysis of adenosine triphosphate 14, ATP, to adenosine diphosphate 15,ADP,is of considerable chemical and biochemical importance since such processes catalyzed by numerous enzymes play a crucial role in... 

Within cells, the hydrolysis of ATP strips off a phosphoryl group from ATP to produce adenosine diphosphate (ADP) ATP +H20 < ADP + HP04... 

The substance that is the immediate source of energy for many biological reactions is adenosine triphosphate (ATP). Although this is a rather large and complex molecule, the business end for the purpose of this discussion is the triphosphate group. Hydrolysis of this group can occur to give adenosine diphosphate (ADP), adenosine monophosphate (AMP), or adenosine itself ... 

In this section we consider the hydrolysis of adenosine triphosphate to adenosine diphosphate and inorganic phosphate, first at a specified pH in the absence of metal ions that are bound and then in the presence of magnesium ions. At... 

Living cells produce L-glutamine by a different reaction pathway using the chemical energy of ATP. ATP undergoes enzymatic hydrolysis to form adenosine diphosphate (ADP) and phosphate (P,). During the hydrolysis of a 1M concentration of ATP, the standard free energy at pH 7.0 and 25°C is measured ... 

ATP An Energy Source When glucose is oxidized in the living cell, the energy released is used to synthesize adenosine triphosphate (ATP), an anhydride of phosphoric acid. As with most anhydrides, hydrolysis of ATP is highly exothermic. The hydrolysis products are adenosine diphosphate (ADP) and inorganic phosphate. 

The NAD glycohydrolase (EC 3.2.2.5) in this study catalyzes the hydrolysis of NAD+ to form nicotinamide, adenosine diphosphate ribose (ADPR), and H+. The assay developed for this activity follows the disappearance of the substrate NAD+ and the production of nicotinamide. 

ATP plays a central role in cellular maintenance both as a chemical for biosynthesis of macromolecules and as the major soirrce of energy for all cellular metabolism. ATP is utilized in numerous biochemical reactions including the eitric acid cycle, fatty acid oxidation, gluconeogenesis, glycolysis, and pyruvate dehydrogenase. ATP also drives ion transporters sueh as Ca -ATPase in the endoplasmic reticulum and plasma membranes, H+-ATPase in the lysosomal membrane, and Na+/K+-ATPase in the plasma membrane. Chemieal energy (30.5 kJ/mol) is released by the hydrolysis of ATP to adenosine diphosphate (ADP). 

Chapters 3-5 have described the calculation of various transformed thermodynamic properties of biochemical reactants and reactions from standard thermodynamic properties of species, but they have not discussed how these species properties were determined. Of course, some species properties came directly out of the National Bureau of Standard Tables (1) and CODATA Tables (2). One way to calculate standard thermodynamic properties of species not in the tables of chemical thermodynamic properties is to express the apparent equilibrium constant K in terms of the equilibrium constant K of a reference chemical reaction, that is a reference reaction written in terms of species, and binding polynomials of reactants, as described in Chapter 2. In order to do this the piiTs of the reactants in the pH range of interest must be known, and if metal ions are bound, the dissociation constants of the metal ion complexes must also be known. For the hydrolysis of adenosine triphosphate to adenosine diphosphate, the apparent equilibrium constant is given by... 

The positive standard free energy implies nonspontaneity for reaction (1). To generate glucose-6-phosphate, reaction (1) is coupled with (2), the hydrolysis of adenosine triphosphate (ATP) to yield adenosine diphosphate (ADP). Reaction (2) has a favorable AG,° < 0 value spontaneous)-. 

More complicated structures that form with longer chains or rings also exist. The biochemically most important polyphosphate is adenosine triphosphate, ATP, which contains three phosphorus tetrahedral units linked by -O-P-0- bonds. The hydrolysis of ATP to adenosine diphosphate, ADP, by the rupture of an 0-P bond releases energy that is used by cells to drive biochemical reactions within the cell. ATP + H2O ADP + HP04 " A//= - 41 kJ... 

Figure 2.4. Hydrolysis of ATP to adenosine diphosphate (ADP) and inorganic phosphate (P,).

Gruber and Lynen found that in the presence of triethylamine the reagent reacts with the free alcoholic group of 2, 3 -isopropylidene-adenosine (1) to give the pyrophosphate ester (2). Hydrolysis, and removal of the isopropylidine group with formic acid gave material containing 22% of adenosine diphosphate (ADP). They... 

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