The action of adenosine triphosphate

In biological cells, the energy released by the oxidation offoods Case study 1.1) is stored in adenosine triphosphate (ATP or ATP , Atlas N3). The essence of ATPs action is its abihty to lose its terminal phosphate group by hydrolysis and to form adenosine diphosphate (ADP or ADP , Atlas N2)  

At pH = 7.0 and 37°C (310 K, blood temperature) the enthalpy and Gibbs energy of hydrolysis are A H = —20 kj moT and Afi = —31 kj moT , respectively. Under these conditions, the hydrolysis of 1 mol ATP (aq) results in the extraction of up to 31 k) of energy that can be used to do non-expansion work, such as the synthesis of proteins from amino acids, muscular contraction, and the activation of neuronal circuits in our brains, as we shall see in Chapter 5. If no attempt is made to extract any energy as work, then 20 kJ (in general, AH) of heat will be produced. 

The Second Law states that the entropy of an isolated system tends to increase. 

In general, the entropy change accompanying the heating of a system is equal to the area under the graph of C/T against Tbetween the two temperatures of interest. 

The Third Law ofthermodynamics states that the entropies of all perfectly crystalline substances are the same at T= 0 (and may be taken to be zero). 

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Derivation Synthesized (1) through the action of adenosine triphosphate, or phosphorus oxychloride, on pyridoxal, and (2) by phosphorylation of pyri-doxamine followed by oxidation with 100% H3P04. 

Mechanical Work. All cells exhibit motile and contractile properties. The remarkable thing about these activities of cells is that they are based on the direct coupling of chemical to mechanical action, in contrast to the heat engines that we have developed to perform our work for us. The mechanisms by which this coupling of chemical to mechanical processes takes place is not well understood, but the hydrolysis of adenosine triphosphate is known to be an important part of the molecular pathway. Although thermodynamic studies cannot provide information about the molecular steps involved, any mechanism that is proposed must be consistent with thermodynamic data [4]. 

As an example of enzyme action, look in Figure 24.11 at the enzyme hexose kinase, which catalyzes the reaction of adenosine triphosphate (ATP) with glucose to yield glucose-6-phosphate and adenosine diphosphate (ADP). The enzyme first binds a molecule of ATP cofactor at a position near the active site, and glucose then bonds to the active site with its C6 hydroxyl group held rigidly in position next to the ATP molecule. Reaction ensues, and the two products are released from the enzyme. 

Animal and bacterial enzymes that utilize or synthesize carbamyl phosphate have activity with acetyl phosphate. Acyl phosphatase hydrolyzes both substrates, and maybe involved in the specific dynamic action of proteins. Ornithine and aspartic transcarbamylases also synthesize acetylornithine and acetyl aspartate. Finally, bacterial carbamate kinase and animal carbamyl phosphate synthetase utilize acetyl phosphate as well as carbamyl phosphate in the synthesis of adenosine triphosphate. The synthesis of acetyl phosphate and of formyl phosphate by carbamyl phosphate synthetases is described. The mechanism of carbon dioxide activation by animal carbamyl phosphate synthetase is reviewed on the basis of the findings concerning acetate and formate activation. 

Figure 13-17. A simpUfled representation illnstrating the likely mode of action of STI571 or Gleevec . STI571 inhibits the binding of adenosine triphosphate (ATP) to the kinase activation domain of Bcr-Abl oncoprotein [64-66].

The cellular mechanism of direct cephalosporin-induced nephrotoxicity may include several possible actions of the cephalosporins. Nephrotoxic cephalosporins are known to induce lipid peroxidation and cellular membrane damage, acylate cellular proteins, and/or interfere with mitochondrial respiration. Mitochondrial respiration appears to be inhibited due to acylation of mitochondrial transporters for metabolic substrates, thereby depriving mitochondria of the necessary intermediates to utilize oxygen. Ultimately, the formation of adenosine triphosphate (ATP), needed to supply cellular energy, also declines to inhibit energy-dependent cellular functions. 

Mitochondria (singular = mitochondrion) are the so-called "power plants" of eukaryotic cells because they are the major source of energy for these cells under aerobic conditions (when oxygen is present). Mitochondria are the sites where complex processes involved in energy generation (such as electron transport and oxidative phosphorylation) are found. The product of mitochondrial action is chemical energy stored in the form of adenosine triphosphate, more commonly called ATP. 

Although interferons are mediators of immune response, different mechanisms for the antiviral action of interferon have been proposed. Interferon-a possesses broad-spectrum antiviral activity and acts on virus-infected cells by binding to specific cell surface receptors. It inhibits the transcription and translation of mRNA into viral nuoleic acid and protein. Studies in cell-free systems have shown that the addition of adenosine triphosphate and double-stranded RNA to extracts of interferon-treated cells activates cellular RNA proteins and a oellular endonuclease. This activation causes the formation of translation inhibitory protein, which terminates production of viral enzyme, nucleic acid, and structural proteins (28). Interferon also may act by blocking synthesis of a cleaving enzyme required for viral release. 

Carnitine serves as a cofactor for several enzymes, including carnitine translo-case and acyl carnitine transferases I and II, which are essential for the movement of activated long-chain fatty acids from the cytoplasm into the mitochondria (Figure 11.2). The translocation of fatty acids (FAs) is critical for the genaation of adenosine triphosphate (ATP) within skeletal muscle, via 3-oxidation. These activated FAs become esterified to acylcamitines with carnitine via camitine-acyl-transferase I (CAT I) in the outer mitochondrial membrane. Acylcamitines can easily permeate the membrane of the mitochondria and are translocated across the membrane by carnitine translocase. Carnitine s actions are not yet complete because the mitochondrion has two membranes to cross thus, through the action of CAT II, the acylcar-nitines are converted back to acyl-CoA and carnitine. Acyl-CoA can be used to generate ATP via 3-oxidation, Krebs cycle, and the electron transport chain. Carnitine is recycled to the cytoplasm for fumre use. 

The susceptibilities of some of these fluorinated purine nucleosides to the action of enzymes are now described. In contrast to the inertness of the 2 -deoxy-2 -fluoro- and 3 -deoxy-3 -fluorocytidine analogs 739, 744, and 821 towards cytidine deaminase, the adenosine compounds 867, 883, and 906 are readily deaminated - by the adenosine deaminase in erythrocytes and calf intestine, but the resulting (deaminated) inosine compounds (from 867 and 883), as well as 888, are highly resistant - to cleavage by purine nucleoside phosphorylase (to give hypoxanthine base for the first two). The reason was discussed. Both 867 and 883 can form the 5 -triphosphates, without deamination, in human erythrocytes or murine sarcoma cells in the presence of 2 -deoxycoformycin, an adenosine deaminase inhibitor, but... 

Luciferase assay. In this technique, firefly luciferase is used to measure small amounts of adenosine triphosphate (ATP) in a bacterial culture, ATP levels being reduced by the inhibitory action of aminoglycoside antibiotics. This method may find more application in the future as more active and reliable luciferase preparations become available. 

Such enzymes catalyse the condensation of specific compounds, accompanied by the breakdown of a pyrophosphate bond in adenosine triphosphate (10.64). Adenosine is the condensation product of a pentose (D-ribofuranose) and a purine (adenine). Scheme 10.15 shows the action of glutamine synthetase on a mixture of L-glutamic acid (10.65) and... 

The role of cyclic 3, 5 -adenosine monophosphate (cAMP) as a second messenger in the actions of catecholamines acting on p-receptors. ATP adenosine triphosphate. 

ZO049 Kobayashi, M., Y. Ishida, N. Shoji, and ZO059 Y. Ohizumi. Cardiotonic action of [8]-gingerol, an activator of the Ca -pumping adenosine triphosphate of sarcoplasmic reticulum, in guinea pig ZO060 atrial muscle. J Pharmacol Exp Ther 1988 246(2) 667-673. 

Phosphorylation and dephosphorylation Phosphorylation reactions are catalyzed by a family of enzymes called protein kinases that use adenosine triphosphate (ATP) as a phosphate donor. Phosphate groups are cleaved from phosphorylated enzymes by the action of phosphoprotein phosphatases (Figure 5.18). 

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