Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We evaluated the effects of exposure to high cholesterol levels for 3 h on arterial smooth muscle responses to adrenergic stimulation. Femoral arteries from Dutch belted rabbits were perfused in vitro with a constant-flow variable-pressure perfusion apparentus. After equilibration the vessels were perfused for 180 min more with media supplemented with cholesterol-phospholipid (C/PL) liposomes of molar ratios of 2:1 or 0.5:1. Although resting vascular resistance was unchanged, norepinephrine (NE) concentration-response analyses revealed a fivefold increase in NE sensitivity (P less than 0.001) in the arteries perfused with the cholesterol-enriched liposomes (2:1) compared with control arteries perfused with the 0.5:1 liposome medium. The arteries perfused with the cholesterol-enriched liposomes demonstrated a 60% increase in cholesterol content and a marked (90%) reduction in Na+-K+-ATPase activity. The increased sensitivity of the cholesterol-enriched arteries was not mediated by acute reductions in Na-pump activity, altered endothelial function, adrenergic nerve function, or prostaglandin production. Cholesterol-induced sensitization to NE did demonstrate an absolute dependence on extra-cellular calcium. These findings suggest that an increase in the free cholesterol content of the arterial smooth muscle cell plasma membrane alters membrane permeability to extracellular calcium during adrenergic stimulation.
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PMID:Cholesterol-induced changes in rabbit arterial smooth muscle sensitivity to adrenergic stimulation. 207 95

Cholesterol, cholesterol-5 alpha, 6 alpha-epoxide, cholesterol-5 beta, 6 beta-epoxide and cholestane-3 beta,5 alpha,6 beta-triol were tested for their ability to induce mutations at the Na+/K+-ATPase loci of the Chinese hamster V79 cells. None of these compounds induced ouabain-resistant mutations compared to the background mutation frequency in the control cells. These compounds were further tested for their ability to inhibit intercellular communication, using the Chinese hamster V79 cell metabolic cooperation assay. The diastereomeric epoxides and cholestane-triol, but not cholesterol, were found to be inhibitors of intercellular communication in a manner similar to other known tumor promoters.
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PMID:Effect of cholesterol epoxides on the inhibition of intercellular communication and on mutation induction in Chinese hamster V79 cells. 284 16

We have recently reported the reconstitution of the clathrin-coated vesicle proton-translocating complex with liposomes prepared from ethanol-extracted crude bovine brain lipids. Reconstitution of proton pumping by the isolated proton ATPase has now been achieved with liposomes prepared from pure lipids. Optimal proton pumping, as assessed by ATP-generated acridine orange quenching and 32Pi-ATP exchange, is achieved with liposomes prepared from phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and cholesterol at a weight ratio of 40:26.5:7.5:26, and a lipid-to-protein weight ratio of 200:1. Under such conditions, the extent of decrease of ATP-generated acridine orange quenching is 150-fold greater than that of native clathrin-coated vesicles. Cholesterol is required to stabilize the proteoliposome. Phosphatidylserine, which is most effective in activating ATP-hydrolytic activity of the solubilized enzyme, is not obligatory for reconstitution of proton pumping.
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PMID:Lipid requirements for reconstitution of the proton-translocating complex of clathrin-coated vesicles. 287 29

Enrichment of the inner mitochondrial membrane with cholesterol induces an increase in ATPase activity with a decrease in the Km for ATP. Cholesterol also abolishes the discontinuity normally found in the Arrhenius plot of ATPase activity. Since no change is detected in the rate of proton translocation through the ATPase membrane sector, it is concluded that cholesterol incorporation induces changes in the hydrolytic step of ATPase via a conformational change transmitted from the membrane sector to the catalytic sector F1.
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PMID:Effects of cholesterol on the kinetics of mitochondrial ATPase. 293 53

A steady-state fluorescence polarization technique, using the membrane probe 1,6-diphenyl-1,3,5-hexatriene (DPH), showed that separately detectable transitions occurred in the regions of 17, 26 and 36 degrees C in isolated preparations of ram sperm plasma membrane. An independent technique based on the temperature-related behaviour of calcium- and magnesium-activated ATPase detected a single phase transition in the region of 24 degrees C. Modulation of ATPase by neighbouring lipid composition was inferred from findings that phospholipase A2 caused significant stimulation of the enzyme. Cholesterol-rich liposomes caused an upward shift of the phase-transition temperature from 24 degrees C to 30 degrees C, but the reasons for this are unclear. It is considered that these phase transitions may have profound effects on sperm survival and physiology, both during normal fertilization processes and in response to cryostorage.
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PMID:Thermotropic phase transitions in the plasma membrane of ram spermatozoa. 294 73

There is correlative evidence that one mechanism of cellular thermoresistance is an increased level of membrane cholesterol. The hypothesis that cholesterol protects membrane proteins from thermal inactivation was tested using Ca-ATPase as a model. The intracellular Ca2+- and Mg2+-dependent ATPase from muscle sarcoplasmic reticulum was reconstituted into lipid mixtures containing different amounts of cholesterol [cholesterol/phospholipid molar ratio (C/PL) = 0.1 or 0.3]. The rate of thermal inactivation of calcium uptake activity of the reconstituted vesicles with C/PL = 0.3 was found to be significantly lower than those with C/PL = 0.1 in the temperature range 43-47 degrees C where hyperthermic cell killing occurs. At 43 degrees C, this is equivalent to a 3 degrees C temperature shift. ATP hydrolysis of Ca-ATPase was found to be substantially heat resistant in reconstituted vesicles with C/PL = 0.1 or 0.3. Glycerol (10%) protects while ethanol (2.5%) and the local anesthetics dibucaine, tetracaine, and procaine sensitize the thermal inactivation of calcium uptake. To investigate the molecular mechanisms of thermal inactivation and cholesterol protection, the responses of the physical state of the lipid and protein conformation to hyperthermic sensitizers and protector were monitored using fluorescent and spin label probes and circular dichroism, respectively. The calcium uptake inactivation appears to be due to a direct thermotropic conformational change (denaturation) of the protein. Cholesterol raises the temperature of inactivation, as does glycerol, while ethanol and the local anesthetics lower it.
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PMID:Protection of the membrane calcium adenosine triphosphatase by cholesterol from thermal inactivation. 294 27

Heart sarcolemmal membranes were isolated by the sucrose density gradient method from rats with chronic diabetes induced by a streptozotocin (65 mg/kg iv) injection. Na+-dependent Ca2+-uptake activities were significantly depressed in diabetic sarcolemmal membranes; such alterations were evident at different incubation times and at different concentrations of Ca2+. Administration of insulin to diabetic rats normalized the Na+-dependent Ca2+-uptake activities. ATP-dependent Ca2+ accumulation and Ca2+-stimulated Mg2+-dependent ATPase, which represents Ca2+-pump mechanisms, were significantly depressed in sarcolemmal preparations for diabetic rats and these changes were also reversible upon insulin treatment. An increase in lysophosphatidylcholine and a decrease in phosphatidylethanolamine as well as diphosphatidylglycerol contents were observed in heart membranes isolated from diabetic rats but other phospholipids were unchanged. Cholesterol-to-phospholipid ratio was significantly increased in preparations from diabetic rats. These results indicate a depression in the ability of the cell to remove Ca2+ through Na+-Ca2+ exchange and Ca2+-pump mechanisms in sarcolemma, and these defects may contribute to the occurrence of intracellular Ca2+ overload and diabetic cardiomyopathy.
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PMID:Sarcolemmal Ca2+ transport in streptozotocin-induced diabetic cardiomyopathy in rats. 295 89

The influence of lipid composition on the activity and temperature dependence of the purified (Na+ + Mg2+)-ATPase from Acholeplasma laidlawii B membranes has been investigated. The reconstituted enzyme requires liquid-crystalline lipid for full activity. However, phosphatidylcholines with fatty acids varying considerably in chemical structure and chain length all support comparable levels of activity at temperatures above their gel to liquid-crystalline phase transition temperatures, indicating that the specific activity of this ATPase is not dependent on membrane lipid fluidity. Phosphatidylethanolamines also effectively reconstitute this enzyme but anionic phospholipids do not, and in fact inhibit enzyme activity when mixed with zwitterionic phospholipids. The incorporation of cholesterol into phosphatidylcholine vesicles had no effect on ATPase activity except at high concentrations, where some inhibition occurs. Cholesterol also affects the temperature dependence of this enzyme somewhat, probably through its effect on the phase state of the phospholipids.
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PMID:Lipid modulation of the activity and temperature dependence of the purified (Na+ + Mg2+)-ATPase from Acholeplasma laidlawii B membranes. 295 35

Cholesterol, phospholipid and lipid peroxide levels in plasma and erythrocytes as well as membrane-bound (Na+ + K+)-ATPase activity were determined in rabbits fed a high-cholesterol diet for 3 months. While cholesterol feeding caused an increase in lipid peroxide levels, (Na+ + K+)-ATPase activity was found to be reduced. According to this, we can assume that, in high-cholesterol fed rabbits, elevated lipid peroxides may be one of the responsible factors for the decreased erythrocyte (Na+ + K+)-ATPase activity.
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PMID:Erythrocyte lipid peroxidation and (Na+ + K+)-ATPase activity in cholesterol fed rabbits. 302 49

The human red blood cell was used as a model system in order to study the effect of cholesterol and its medically important oxidized derivatives (OSC = oxidized sterol compounds) on the calcium entry channel. The calcium-ejecting adenosine triphosphatase (ATPase) was inhibited by vanadate and the influx of 45Ca2-into the cells measured. The cells were loaded with OSC at concentrations between 0.075 and 1.5 micrograms OSC/10(7) cells. Two classes of OSC could be distinguished: one stimulating Ca2+ influx dose-dependently by almost 100% at maximum concentrations, the other inhibiting it dose-dependently by up to 80%. The calcium channel blocker nitrendipine inhibited influx by 70% at 15 microM. More than 90% of the total stimulation or inhibition was accounted for by an influence on the nitrendipine-inhibitable part of influx, i.e. the calcium channel. Cholesterol (incorporated using liposomes) had a stimulatory (+288%), cholesterol depletion an inhibitory effect on calcium influx (-18%). These results demonstrate that cholesterol and its oxidized derivatives modulate the calcium channel in a highly stereospecific manner and provide new insights into the mechanism of action and the atherogenic effect of these compounds.
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PMID:Cholesterol and its oxidized derivatives modulate the calcium channel in human red blood cells. 610 Jul 51


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