Calcium-adenosine triphosphatase

Contraction of muscle follows an increase of Ca " in the muscle cell as a result of nerve stimulation. This initiates processes which cause the proteins myosin and actin to be drawn together making the cell shorter and thicker. The return of the Ca " to its storage site, the sarcoplasmic reticulum, by an active pump mechanism allows the contracted muscle to relax (27). Calcium ion, also a factor in the release of acetylcholine on stimulation of nerve cells, influences the permeabiUty of cell membranes activates enzymes, such as adenosine triphosphatase (ATPase), Hpase, and some proteolytic enzymes and facihtates intestinal absorption of vitamin B 2 [68-19-9] (28). 

Thompson JD, Nechay BR. 1981. Inhibition by metals of a canine renal calcium, magnesium activated adenosine triphosphatase. J Toxicol Environ Health 7 901-908. 

Levy, J., Zhu, Z., and Dunbar, J. C., 1998, The effect of glucose and calcium on Ca2+-adenosine triphosphatase in pancreatic islets isolated from a normal and a non-insulin-dependent diabetes mellitus rat model. Metabolism, 47 185-9. 

Potter, J. D., and Gergely, J. (1975). The calcium and magnesium binding sites on troponin and their role in the regulation of myofibrillar adenosine triphosphatase. / Biol. Chem. 250, 4628-4633. 

Synthetic membranes as used for filtration and microfiltration were analyzed by STM " 80-nm pores were observed. The three-dimensional crystals — Ca-adenosine triphosphatase (Ca-ATPase) — of the calcium pump from sarcoplasmic reticulum were imaged by AFM. ... 

Caldesmon is a cytoplasmic protein with two isoform classes, one of which is found predominantly in smooth muscle cells and other cell types with partial myogenic differentiation. High-molecular-weight isoforms with molecular weights between 89 and 93 kD are capable of binding to actin, tropomyosin, calmodulin, myosin, and phospholipids, and they function to counteract actin-tropomyosin-activated myosin adenosine triphosphatase (ATPase). As such, they are mediators for the inhibition of calcium-dependent smooth muscle contraction." ... 

Pfleger H, Wolf HU. 1975. Activation of membrane-bound high-affinity calcium ion-sensitive adenosine triphosphatase of human erythrocytes by bivalent metal ions. Biochem J 147 359-361. 

At relevant inotropic and vasorelaxant concentrations, milrinone is a selective inhibitor of peak III cAMP phosphodiesterase isozyme in cardiac and vascular muscle. This inhibitory action is consistent with cAMP-mediated increases in intracellular ionized calcium and contractile protein phosphorylation and relaxation in vascular muscle. Additional experimental evidence also indicates that milrinone is not a beta-adrenergic agonist nor does it inhibit sodium-potassium adenosine triphosphatase activity as do the digitalis glycosides. 

Another possibility deserving consideration is that some of the phytoestrogen effects may be attributable to properties that do not involve estrogen receptors, such as effects on enzymes, protein synthesis, cell proliferation, angiogenesis, calcium transport, Na /K adenosine triphosphatase, growth factor action, vascular smooth muscle cells, lipid oxidation, and cell differentiation. Some of these properties will be further discussed. 

This enzyme activity has been observed in myosin and actomyosin, mitochondria, microsomes, and cell membranes. In some cases magnesium ions function as an activator, in others calcium ions, and in still others, both calcium and magnesium are requited. Another form of adenosine-triphosphatase is stimulated by sodium and potassium ions and is inhibited by ouabain. Some forms of the enzyme can hydrolyse inosine triphosphate and other nucleoside-5 -triphosphates. The substrate specificity may depend upon the activating divalent cation and on the presence of monovalent cations. These enzymes are probably important components of a system responsible for facilitating cation transfer in membranes. They should not be confused with adenosine triphosphate pyrophosphatase E.C. 3.6.1.8. 

The circulating and intracellular calcium participate in many vital metabolic reactions muscle contraction, neuromuscular excitability, blood coagulation, adenosine triphosphatase activations, and other reactions. 

Calcium stimulates myosin-adenosine triphosphatase (ATPase) activity. 

In order to function, some enzymes require a metal (such as calcium), or a nonmetal, or both, attached to them, either loosely or tightly others function independently. For example, calcium activates a number of enzymes including pancreatic lipase, adenosine triphosphatase, and some proteolytic enzymes. 

A low intake of magnesium may also contribute to a higher mortality of cardiovascular disease in soft water areas. Magnesium -and also calcium - are involved in enzyme systems in the heart muscle. Sealig (1972) (54) has shown for example that inadequate magnesium concentration interferes with the activation of adenosin-triphosphatase and causes a loss of potassium by myocardial cells. This might be responsible for sudden death from coronary artery disease. 

This area also has been covered recently. Several techniques, including Li NMR, have been used to study sarcoplasmic reticular calcium ion transport adenosine triphosphatase. The lithium relaxation rate is high in the presence of the Gd " form of the enzyme because the two ions are close together. Adding Ca " reduces the lithium relaxation rate as Gd " is displaced. Ion-ion distances are estimated. Comparison of the relaxation rates of Li with Li on the Mn " form of pyruvate kinase allows the molecular correlation time to be estimated at 3700 ps so that the Mn-Li distance must be 570 20 pm. Na NMR in the presence of DNA favors the theory that the... 

Istaroxime is a steroidal drug that improves cellular calcium cycling. The drug has a dual activity. Firstly, SERC A2a (SR Ca -ATPase or adenosine 5 triphosphatase) stimulation causes rapid Ca + sequestration in sarcoplasmic... 

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