Enzymes Adenylate kinase

Figure 4.14 Examples of different types of open twisted a/p structures. Both schematic and topological diagrams are given. In the topological diagrams, arrows denote strands of p sheet and rectangles denote a helices, (a) The FMN-binding redox protein flavodoxln. (b) The enzyme adenylate kinase, which catalyzes the reaction AMP +...

AMP reverses the inhibition due to ATP, and AMP levels in cells can rise dramatically when ATP levels decrease, due to the action of the enzyme adenylate kinase, which catalyzes the reaction... 

For luciferin, a firefly luciferase cosubstrate, another method of retention has been evaluated which consisted of incorporating the substrate in acrylic microspheres during their formation, these last being then confined in a polymeric matrix31. Using the suitable co-immobilized enzymes (adenylate kinase and creatine kinase), the three adenylic nucleotides (ATP, ADP and AMP) could be assayed continuously and reproducibly with a selfcontainment working time of 3 h. 

Mechanisms to increase ATP generation The two processes that increase ATP generation are glycolysis and oxidative phosphorylation. The latter is due to increased oxygen supply due to vasodilation (see below). The signals that stimulate glycolysis are increases in the concentrations of AMP and phosphate and a decrease in the level of phos-phocreatine. These changes occur as follows. The three nucleotides, ATP, ADP and AMP are in equilibrium, catalysed by the enzyme adenylate kinase, as follows ... 

Since the regeneration of ATP from AMP requires a molecule of ATP to convert AMP to ADP (a reaction catalyzed by the enzyme adenylate kinase), a total of four molecules of ATP are hydrolyzed in the synthesis of one molecule of urea. 

Why is AMP and not ADP the positive regulator of phosphofructokinase When ATP is being utilized rapidly, the enzyme adenylate kinase (Section 9.4) can form ATP from ADP by the following reaction ... 

Fig. 5.8. Stereochemical course of ATP hydrolysis by Fj. The chiral [ 0, O, 0]-thiophosphate librated was converted into ATPjSS by successive treatments with glycolytic enzymes, adenylate kinase and glycolytic enzymes. The resulting ATP/8S were analyzed by P-NMR [164].

Controversy exists concerning the cause and effect relationships between deficiencies of the enzymes adenylate kinase (AK EC 2.7.4.3) and adenosine triphosphatase (ATPase EC 3.6.1.3) and hemolytic disease. Since the consensus seems to be that there is no association, these enzymes will not be discussed here. 

Ans. AMP, adenosinemonophosphate, cannot be phosphorylated by either substrate level or oxidative phosphorylation, but can react with another mole of ATP catalyzed by the enzyme adenylate kinase as ... 

A major function of the Bcl-2 family members is to regulate cytochrome c release via their interaction with the outer mitochondrial membrane. As described above, cytochrome c release is an important first step in initiating apoptotic events in cells because of its ability to interact with and thereby activate Apaf-1. However, mitochondria can also release a number of other proteins during apoptosis, such as AIF, certain procaspases, catabolic enzymes, adenylate kinase 2 and SMAC/Diablo. The role of these proteins in the apoptotic process is not known with certainty. Anti-apoptotic proteins of the Bcl-2 family possess membrane anchoring domains at their carboxy terminus that target the... 

Assays for enzymes (adenylate kinase, ATPase, creatine kinase, creatine kinase isoenzyme MB, lactate dehydrogenase, proteases)... 

But the concentrations of AMP, ADP and ATP remain constant in the stationary state in mitodiondria during active oxidative phosphorylation. So apparently thwe is a control of oxidative pho horylation by means of a regulation of the entry of nucleotide phosphate acceptors. According to Siekevitz and Potter, this entry is under the control of an enzyme situated in the outa r ion of the mitochondria, this enzyme, adenylic kinase, catalyses the establishment of equilibritun between AMP, ADP and ATP. 

These reactions are catalyzed by the enzymes nucleoside monophos-phokinase and nucleoside diphosphokinase, respectively. Note that these reactions are reversible, so that ATP may be synthesized at the expense of GTP or another nucleoside triphosphate. The precursor ADP (adenosine diphosphate) may also be synthesized from the reaction of AMP with ATP, catalyzed by the enzyme adenylate kinase ... 

In many tissues, the three nucleotides are maintained in equilibrium by the enzyme adenylate kinase which catalyses the reaction. 

Murant, R.S., Gibson, S.L., and Hilf, R., Photosensitizing effects of Photofrin II on the site-selected mitochondrial enzymes adenylate kinase and monoamine oxidase. Cancer Res., 47, 4323, 1987. 

Mitochondria are surrounded by a simple outer membrane and a more complex inner membrane (Figure 21.1). The space between the inner and outer membranes is referred to as the intermembrane space. Several enzymes that utilize ATP (such as creatine kinase and adenylate kinase) are found in the intermembrane space. The smooth outer membrane is about 30 to 40% lipid and 60 to 70% protein, and has a relatively high concentration of phos-phatidylinositol. The outer membrane contains significant amounts of porin —a transmembrane protein, rich in /3-sheets, that forms large channels across the membrane, permitting free diffusion of molecules with molecular weights of about 10,000 or less. Apparently, the outer membrane functions mainly to... 

Adenylate kinase (AK) is a ubiquitous monomeric enzyme that catalyzes the interconversion of AMP, ADP, and ATP. This interconversion of the adenine nucleotides seems to be of particular importance in regulating the equilibrium of adenine nucleotides in tissues, especially in red blood cells. AK has three isozymes (AK 1,2, and 3). AK 1 is present in the cytosol of skeletal muscle, brain, and red blood cells, and AK 2 is found in the intermembrane space of mitochondria of liver, kidney, spleen, and heart. AK 3, also called GTP AMP phosphotransferase, exists in the mitochondrial matrix of liver and heart. 

B15. Beutler, E., Carson, D., Dannawi, H., Forman, L., Kuhl, W., West, C., and Westwood, B., Metabolic compensation for profound erythrocyte adenylate kinase deficiency A hereditary enzyme defect without hemolytic anemia. J. Clin. Invest. 72,648-655 (1983). 

Adenosine triphosphate (ATP) is one of the most important cofactors involved in many of the synthetic reactions going on within the cell. Its recent large scale in vitro enzymatic synthesis from adenosine and acetylphosphate is of particular interest. Three enzymes immobilized in polyacrylamide gel were used adenosine kinase, adenylate kinase and acetate kinase (lip. ... 

In the preceding sections the conversion of purines and purine nucleosides to purine nucleoside monophosphates has been discussed. The monophosphates of adenosine and guanosine must be converted to their di- and triphosphates for polymerization to RNA, for reduction to 2 -deoxyribonucleoside diphosphates, and for the many other reactions in which they take part. Adenosine triphosphate is produced by oxidative phosphorylation and by transfer of phosphate from 1,3-diphosphoglycerate and phosphopyruvate to adenosine diphosphate. A series of transphosphorylations distributes phosphate from adenosine triphosphate to all of the other nucleotides. Two classes of enzymes, termed nucleoside mono-phosphokinases and nucleoside diphosphokinases, catalyse the formation of the nucleoside di- and triphosphates by the transfer of the terminal phosphoryl group from adenosine triphosphate. Muscle adenylate kinase (myokinase)... 

Because many cells maintain ATP, ADP, and AMP concentrations at or near the mass action ratio of the adenylate kinase reaction, the cellular content of this enzyme is often quite high. A consequence of such abundance is that, even after extensive purification, many proteins and enzymes contain traces of adenylate kinase activity. The presence of this kinase can confound the quantitative analysis of processes that either require ADP or are carried out in the presence of both ATP and AMP. Furthermore, the equilibrium of any reaction producing ADP may be altered if adenylate kinase activity is present. To minimize the effect of adenylate kinase, one can utilize the bisubstrate geometrical analogues Ap4A and ApsA to occupy simultaneously both substrate binding pockets of this kinase . Typical inhibitory concentrations are 0.4 and 0.2 mM, respectively. Of course, as is the case for the use of any inhibitor, one must always determine whether Ap4A or ApsA has a direct effect on a particular reaction under examination. For example. Powers et al studied the effect of a series of o ,co-di-(adenosine 5 )-polyphosphates (e.g., ApnA, where n =... 

Selected entries from Methods in Enzymology [vol, page(s)] Adenylate kinase contamination in in phosphotransferases, 63, 7 as contaminant enzyme preparations, 64, 24 P, P -di(adenosine-5 )-tetraphosphate and P, P -di(adenosine-5 )-pentaphosphate inhibition of adenylate kinase, 63, 7, 401, 483. 

This enzyme [EC 2.7.4.11] catalyzes the reaction of ATP with dAMP to produce ADP and dADP. The enzyme can also use AMP as a substrate (thus producing another ADP as a product hence, an activity identical to that of adenylate kinase). 

In a number of cases there may be a contaminating enzyme present which acts on one or more of the substrates, products, or effectors of the system under study. It may be necessary to include in the reaction mixture a specific inhibitor for that contaminating activity. For example, adenylate kinase is often present in preparations of a number of phosphotransferases. It is often advantageous, in such instances, to include a specific inhibitor of adenylate kinase (e.g., P, P -di(adenosine-5 )-tetraphosphate or P P -di(adenosine-5 )-pentapho-sphate). If an inhibitor of the contaminating activity is added as an additional constituent of the reaction mixture, the investigator should demonstrate that the inhibitor is not an effector of the enzyme under study. 

Quite a few enzymes have been reported to have this reaction scheme for example, hexokinase, adenylate kinase, and phosphofructokinase. ... 

ADP as a substrate in enzyme reactions, ADENYLATE KINASE (or MYOKINASE) ATP SYNTHASE CREATINE KINASE NUCLEOSIDE DIPHOSPHATE KINASE PHOSPHOGLYCERATE KINASE PYRUVATE KINASE RIBONUCLEOTIDE REDUCTASE SULFATE ADENYLYLTRANSFERASE (ADP) [ADP]/[ATP] ratio,... 

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