Adenosine triphosphatase ATPase

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). 

The ventricular action potential is depicted in Fig. 6-2.2 Myocyte resting membrane potential is usually -70 to -90 mV, due to the action of the sodium-potassium adenosine triphosphatase (ATPase) pump, which maintains relatively high extracellular sodium concentrations and relatively low extracellular potassium concentrations. During each action potential cycle, the potential of the membrane increases to a threshold potential, usually -60 to -80 mV. When the membrane potential reaches this threshold, the fast sodium channels open, allowing sodium ions to rapidly enter the cell. This rapid influx of positive ions... 

An in-depth study of DNA repair systems (Aravind et al., 1999a) has concluded that few, if any, repair proteins occur with identical collinear domain arrangements in all three kingdoms of life. Approximately 10 enzyme families of adenosine triphosphatases (ATPases), photolyases, helicases, and nucleases were identified that are all likely to have been present in the cenancestor. These enzymatic domains are accompanied in DNA repair proteins by numerous regulatory domains. This indicates that the domain architectures of these proteins are labile, with incremental addition and/or subtraction of domains to conserved cores to be a common phenomenon except in the most closely related species. 

The catecholamines can play an important role in the short-term regulation of plasma potassium levels. Stimulation of hepatic a-adrenoceptors will result in the release of potassium from the liver. In contrast, stimulation of (32-adrenoceptors, particularly in skeletal muscle, will lead to the uptake of potassium into this tissue. The (32-adrenoceptors are linked to the enzyme Na"", K+ adenosine triphosphatase (ATPase). Excessive stimulation of these (32-adrenoceptors may produce hypokalemia, which in turn can be a cause of cardiac arrhythmias. 

For many years, niclosamide (Niclocide) was widely used to treat infestations of cestodes. Niclosamide is a chlorinated salicylamide that inhibits the production of energy derived from anaerobic metabolism. It may also have adenosine triphosphatase (ATPase) stimulating properties. Inhibition of anaerobic incorporation of inorganic phosphate into ATP is detrimental to the parasite. Niclosamide can uncouple oxidative phosphorylation in mammalian mitochondria, but this action requires dosages that are higher than those commonly used in treating worm infections. 

Strong sensory stimuli (e.g. 90 dB sound) can precipitate tonic-clonic seizures in some strains of mice, the DBA/2 strain being particularly susceptible, while posturally induced seizures in "epileptic-like" mice have been extensively studied and have been shown to be associated with abnormalities in both the adenosine triphosphatases (ATPases) and various biogenic amine neurotransmitters. 

Schistocephalus solidus has its plerocercoid stage in an ectotherm (the fish Gasterosteus aculeatus) and its adult stage in an endoderm (a fish-eating bird) and it serves as an excellent model for the study of temperature adaptation in parasites. Walker Barrett (922,923) have studied the effect of temperature on (a) the activities of the mitochondrial enzyme adenosine triphosphatase (ATPase) and (b) the physical state of mitochondrial membranes in adult and larval S. solidus. 

Adenylate cyclase is considered as a second messenger that catalyzes the formation of cAMP (cyclic adenosine monophosphate) from ATP this results in alterations in intracellular cAMP levels that change the activity of certain enzymes—that is, enzymes that ultimately mediate many of the changes caused by the neurotransmitter. For example, there are protein kinases in the brain whose activity is dependent upon these cyclic nucleotides the presence or absence of cAMP alters the rate at which these kinases phosphorylate other proteins (using ATP as substrate). The phosphorylated products of these protein kinases are enzymes whose activity to effect certain reactions is thereby altered. One example of a reaction that is altered is the transport of cations (e.g., Na+, K+) by the enzyme adenosine triphosphatase (ATPase). 

Cyclodienes appear to act more in the central nervous system than in the peripheral nervous system. One major mode of action is the inhibition of y-aminobutyric acid-regulated Cl ion flux in neurons. Cyclodienes also exert effects on membrane-bound adenosine triphosphatases (ATPases), altering Na, K" ", and Ca " " ion transport. The result is a partial depolarization of neurons rather than repolarization... 

The nervous system is the main site of toxicity for DDT. Effects are observed on both the central nervous system (CNS) and peripherally. There is significant alteration of neuronal membrane enzymatic and electrophysiological properties. In particular, sodium channels are altered such that once activated they close slowly, prolonging the depolarization of the nerve by interfering with the active transport of Na ions out of the axon. Potassium channels are also affected. DDT specifically affects Na", K -adenosine triphosphatases (ATPases) and Ca " -AT-Pases, which inhibit repolarization of neurons. The membrane remains partially depolarized and is extremely sensitive to complete depolarization by very small stimuli. DDT also inhibits calmodulin that is necessary for Ca transport essential for the subsequent release of neurotransmitters. 

As with other cyclodiene insecticides, heptachlor blocks the neuronal uptake of chloride ions by blocking the activity of y-aminobutyric acid. This results in only a partial repolarization of activated neurons leading to an uncontrolled excited condition. Additionally, chlordane inhibits Ca, Mg -adenosine triphosphatase (ATPase) and Na,K-ATPase functions, leading to increased concentrations of... 

In vitro studies of gingerol using canine cardiac tissue and rabbit skeletal muscle demonstrated Ca2+-adenosine triphosphatase (ATPase) activation in the cardiac and skeletal sarcoplasmic reticulum (SR) (31). Gingerol (3-30... 

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. 

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