Adenosinetriphosphatase activity

The inhibition of amino-acid transport has been regarded as the main toxic effect of mercury compounds [82], The biochemical mechanism underlying the inhibition is unclear. In unfertilized sea-urchin eggs an interaction with the amino-acid carrier was found, whereas in fertilized eggs inhibition of amino-acid transport was indirect and might result from an elevation of the Na + content of the egg caused by the inhibition of the Na+ pump [83]. The action on the diffusional process could be mediated by an effect on membrane phospholipids or on membrane proteins, or by interaction with Ca2+ which stabilizes membrane structure. Mercuric chloride in skate liver cells inhibited amino acid transport, decreased Na + /K + -ATPase (adenosinetriphosphatase) activity, impaired volume regulatory mechanisms and increased the permeability of the plasma membrane to potassium [84]. It has been suggested that... 

M. Caffrey and G. W. Feigenson, Fluorescence quenching in model membranes. 3. Relationship between calcium adenosinetriphosphatase enzyme activity and the affinity of the protein for phosphatidylcholines with different acyl chain characteristics, Biochemistry 20, 1949-1961 (1981). 

Biain adenosinetriphosphatase This enzymatic activity is persistendy associated with brain micFotubules even after multiple cycles of warm-induced microtubule assembly, centrifugation to separate protomer and polymer, cold-induced disassembly, and subsequent centrifugation to remove cold-stable aggregates (White et aL, 1980). The enzyme hydrolyzes boA GTP and ATP, and recent work by Tominaga and Kaziro (1982) indicates that there are two distinct ATP-ases, one that is of low M, (around 33,000) and tubulin dependent in the presence of calcium ion, and the other of larger size and associated with membrane vesicles... 

There are also several enzymes attached to the plasma membrane which control the structure and fimction of the membrane, and the activities of these enzymes may be controlled by zinc. Adenosinetriphosphatase (ATPase) and phospholipase A2 are known to be inhibited by zinc, and... 

What studies have been performed One of the more interesting of the few studies that exist was the examination of the activity of the Ca2+ adenosinetriphosphatase (ATPase) of sarcoplasmic reticulum membranes that were reconstituted into bilayer vesicles of different, defined lipid compositions (38). This survey found that the activity, which may be defined as the number of Ca2+ pumped across the bilayer per adenosine 5 -triphosphate (ATP) hydrolyzed, correlated strongly with the Hu tendencies of the imbedding lipid bilayer. For example, activities were high in compositions rich in either DOPE or MGDG, both of which readily form low-temperature Hu phases. By contrast, activities were low in DOPC or DGDG, as well as in other lipids that do not readily form Hu phases. Decreasing the amount of... 

Digitalis glycosides block the activity of sodium-potassium adenosinetriphosphatase (ATPase). This inhibits the recovery of the cardiac myocyte from depolarization in a dose-dependent manner. This, in turn, results in a buildup of sodium within the cell and potassium outside of the cell, with successive depolarizations. The increase in intracellular sodium inhibits the membrane sodium-calcium transporter, allowing accumulation of calcium within the cell. The transporter may eventually reverse, and intracellular sodium is exchanged for extracellular calcium (see Figure). The resulting increase in intracellular calcium mediates an increase in the force of contraction of the cardiac muscle. 

Dragiev, M. and V. Ivanchev Changes in the activity of adenosinetriphosphatase and succinic dehydrogenase of the liver, kidneys, heart, and brain of rabbits under the effect of toxic substances forming during tobacco fermentation Gig. Tr. Prof. Zabo 15 (1971) 32-25. 

Since ouabain decreased cation transport and yet stimulated phosphate exchange in phosphatidic acid over a short period, any relationship of this particular lipid to cation transport would be difficult to explain. Digitoxin also enhanced the uptake of labeled phosphate into the phospholipids of rat heart in vivo (Marinetti et al., 1%1) the effect was greatest with ethanolamine phospholipids, but in these experiments the possibility of an increased permeability of the tissue to phosphate was not eliminated. Recent studies have strongly suggested that ouabain inhibits the sodium- and potassimn-activated adenosinetriphosphatase (Chamock and Post, 1963). It may well do this by specifically inhibiting the potassium-dependent phosphorolysis reaction which leads to the release of orthophosphate (see also, McIIwain, 1963). 

Na+ -p K+) Adenosinetriphosphatase is the membrane-bound enzyme that transports sodium and potassium in opposite directions across the cell membrane to create the ion gradients that are utilized to perform physiological functions. The cardiac glycosides and aglycons, such as digoxin, ouabain, and strophanthidin, are natural products that have been used therapeutically for centuries in the treatment of heart disease. Their only known biochemical effect is to inhibit specifically (Na+-j-K ) adenosinetriphosphatase and consequently decrease or completely stop active cation flux. 

There are at least three enzymes which will hydrolyze adenosine triphosphate. Myosin, one of the active proteins of muscle, has very strongly associated with it an adenosinetriphosphatase which is activated by calcium ions and inhibited by magnesium. Cleavage of only the terminal phosphate of ATP occurs, and inosine triphosphate is the only other substrate attacked. Not associated with myosin is a water-soluble adenosinetriphosphatase described by Kielley and Meyerhof. It is strongly... 

Transfer of Phosphate from Phosphocreatine to Glucose—Here phosphocreatine is the donor of phosphate to adenylic acid forming adenosine triphosphate which passes its acid-labile phosphate over to the sugar. The adenylic acid system acts in a catalytic manner as a carrier of phosphate between phosphocreatine and glucose just as it acts catalytically in aerobic phosphorylation as a carrier of inorganic phosphate to the phosphate acceptor. If sufficiently active, adenosinetriphosphatase will interfere with the phosphorylation of the acceptor to a similar extent in both cases. 

Bonting, S. L., Caravaggio, L. L., and Hawkins, N. M., 1962, Studies on sodium-potassium-activated adenosinetriphosphatase. IV. Correlation with cation transport sensitive to cardiac glycosides. Arch. Biochem. Biophys. 98 413. 

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