Magnesium-adenosine triphosphate

Easterbrook-Smith, B Wallace, J.C., Keech, D.B. (1976) Pyruvate Caboxylase Affinity Labeling of the Magnesium Adenosine Triphosphate Binding Site, Eur. J. Biochem. 62,125-130. 

The Fe protein of nitrogenase (molecular weight 64,000) has two subunits and a single Fe4S4 unit. Each subunit folds as a single a/p-type domain. It binds with magnesium adenosine triphosphate (MgATP). 

Pig. 7. Substrate reduction catalyzed by Mo-nitrogenase. Mo-nitrogenase is depicted as the box containing the Fe protein (Fe-p) and MoFe protein (MoFe-p). The required inputs for catalyzed reduction are shown at left. The electron donor is usually sodium dithionite (8204 ) in vitro and either ferredoxin (Fd) or flavodoxin (Fid) in vivo. Other mandatory inputs are protons (H" ) and magnesium adenosine triphosphate (MgATP). The most commonly used substrates (above the horizontal line) and their products (below the hne) are shown at right. The numbers in parentheses are the number of electrons required to effect each reduction shown. The horizontal arrow indicates that CO is an inhibitor of aU catalyzed reactions except for the production of H2 from protons. 

Figure 10-4. Adenosine triphosphate (ATP) shown as the magnesium complex. ADP forms a similar complex with Mg A...

Magnesium is the second most abundant intracellular cation. Magnesium serves as an essential cofactor for numerous enzymes and in many biochemical reactions, including reactions involving adenosine triphosphate (ATP).17 Magnesium disorders can be multifactorial and can be related to renal function, disease... 

Although already in 1947 McElroy discovered that adenosine triphosphate (ATP) and magnesium were essential for the BL reactions by which fireflies produce... 

Another enzyme used for the measurement of glucose is hexokinase (EC 2.7.1.1) which catalyses the phosphorylation of glucose to produce glucose-6-phosphate with adenosine triphosphate as the phosphate donor and magnesium ions as an activator. The rate of formation of glucose-6-phosphate can be linked to the reduction of NADP by the enzyme glucose-6-phosphate dehydrogenase (EC 1.1.1.49). This indicator reaction can be monitored spectrophotometrically at 340 nm or fluorimetrically ... 

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 ... 

For example, Bachelard used [Mgtotai]/[ATPtotai ] = 1 in his rate studies, and he obtained a slightly sigmoidal plot of initial velocity versus substrate ATP concentration. This culminated in the erroneous proposal that brain hexokinase was allosterically activated by magnesium ions and by magnesium ion-adenosine triphosphate complex. Purich and Fromm demonstrated that failure to achieve adequate experimental control over the free magnesium ion concentration can wreak havoc on the examination of enzyme kinetic behavior. Indeed, these investigators were able to account fully for the effects obtained in the previous hexokinase study. ... 

Magnesium ions are also involved in biological processes and occur in cells at millimolar concentrations [315]. Magnesium can be estimated based on the chemical shift difference of the resonances of adenosine triphosphate (ATP) using P NMR [316-318], though P NMR has intrinsically low signal-to-noise, exacerbated under many pathophysiological conditions, such as ischemia. 

Niwaguchi et al. (14-16) reported that when rat liver homogenates were incubated in a system containing 14C-L-glutamate, glucose, DPN, adenosine triphosphate (ATP), magnesium ions, cytochrome c, and fu-marate, an acidic compound was formed which could be identified as pyrrolidone carboxylic acid by infrared spectroscopy, electrophoresis,... 

Reactions involving the formation and hydrolysis of phosphate and polyphosphate esters are of vital importance in biological systems in which it is found that magnesium ions are almost invariably implicated. The formation and decomposition of adenosine triphosphate are the fundamental reactions involved in energy storage in living systems. In this context, it is perhaps relevant to note that the hydrolysis of ATP is enhanced, albeit in a very modest manner, by some cobalt(m) complexes. 

Proteinoid microspheres containing zinc hydrolyze the natural substrate, adenosine triphosphate (ATP) as well as the unnatural substrates, p-nitrophenylacetate or p-nitrophenyl phosphate. The significance resides in the fact that the energy for most biosyntheses is provided by the hydrolysis of ATP. Zinc, magnesium and other metal salts are known to catalyze the hydrolysis of ATP 10). Proteinoid microspheres containing zinc as a cofactor have an activity for hydrolysis of ATP 11 12). 

Production of Hydrogen Ions and Magnesium Ions in the Hydrolysis of Adenosine Triphosphate... 

BINDING OF HYDROGEN IONS AND MAGNESIUM IONS BY ADENOSINE TRIPHOSPHATE... 

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... 

To 17 parts by volume of the crude enzyme solution are added 5 parts of kanamycin B, 50 parts by volume of 0.5 M phosphate buffer (pH 7.0), 100 parts by volume of 1 M adenosine triphosphate solution, 50 parts by volume of 0.1 M magnesium acetate solution and 50 parts by volume of 0.1 M 2-mercaptoethanol, which is filled up to 500 parts by volume with distilled water. The mixture is subjected to enzymic reaction at 37°C for 20 h. 

CPSI catalyzes the formation of carbamoyl phosphate from bicarbonate, ammonium, and two adenosine triphosphate molecules (Fig. 18-1).This first step of the urea cycle occurs in the mitochondrial matrix and assimilates the first of the two nitrogen atoms that will eventually be found in urea. While two ATP molecules are hydrolyzed, there is formation of a lower energy bond in carbamoyl phosphate. CPSI is a homodimer that accounts for 15-30% of the total protein mass in liver mitochondria. jV-Acetylglutamate (NAG) is an essential allosteric activator of CPSI activity, and magnesium ions are also required for its activity. 

Li, Z.-S., Zhao, Y. and Rea, RA. (1995) Magnesium adenosine 5 -triphosphate-energized transport of glutathione-S-conjugates by plant vacuolar membrane vesicles. Plant Physiol, 107,1257-68. 

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