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)

To investigate the functional stages of osteoclasts, the ultrastructural histochemical distribution of the lysosomal enzymes [acid phosphatase (tartrate-sensitive) and neutral phosphatase], the plasma membrane enzymes [alkaline phosphatase, Ca(++)-ATPase, and alkaline ouabain-insensitive p-nitrophenylphosphatase (alkaline p-NPPase)], and the mitochondrial enzyme (cytochrome C oxidase) was evaluated in the chicken tibial metaphysis. Both active-appearing and detached (resting) osteoclasts were studied. Serial sectioning was used to identify detached osteoclasts which were present in the perivascular space. The ultrastructure of detached osteoclasts was similar to that of active osteoclasts, except for the lack of a ruffled border and clear zone, and an altered distribution pattern of small vesicles. Small vesicles were uniformly distributed in the cytoplasm of resting osteoclasts, whereas they were concentrated beneath the ruffled border of active osteoclasts. Alkaline p-NPPase, a marker enzyme for the basal ruffled border, was also apparent on the membrane of small vesicles. However, the vesicles did not possess Ca(++)-ATPase, a marker enzyme for the apical plasma membrane. These findings support the concept that small vesicles serve as a membrane reservoir for the ruffled border membrane. Pre-osteoclasts contained abundant mitochondria and lysosomes, prominent Golgi complexes, moderately developed endoplasmic reticulum, and lacked small vesicles. Pre-osteoclasts appear to fuse with osteoclasts which are attached to the bone surface, but not with detached osteoclasts. The small vesicles, from which the ruffled border arises, are absent from pre-osteoclasts, suggesting that they develop after fusion with pre-existing osteoclasts or after attachment to the bone surface. Alkaline p-NPPase appears to be a marker for differentiation of pre-osteoclasts to mature osteoclasts.
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PMID:Characterization of the functional stages of osteoclasts by enzyme histochemistry and electron microscopy. 166 72

A semi-naphthoquinone natural product, A80915A, produced by Streptomyces aculeolatus was found to be a potent inhibitor of gastric (H(+)-K+)-ATPase, the enzyme responsible for acid secretion in the stomach. Enzyme activity was measured by potassium-stimulated hydrolysis of ATP or p-nitrophenolphosphate with enzyme prepared from the stomach fundic mucosa of pigs. Concentration-dependent inhibition was observed with an IC50 of about 2-3 microM for both ATPase and p-nitrophenylphosphatase. A Hill plot indicated that the enzyme has two binding sites for A80915A. Inhibition was not affected by the presence of the reducing agent dithiothreitol, indicating a lack of involvement of enzyme sulfhydryl groups. A 30-min incubation of enzyme with increasing drug concentrations followed by a 10-fold dilution did not alter the IC50, indicating that A80915A does not covalently modify the enzyme. Coincubation of enzyme with 3.8 microM A80915A resulted in time-dependent inhibition. The rate of inhibition was slowed significantly by the presence of 20 mM potassium, rubidium and ammonium but not by 20 mM sodium, lithium and choline, or by 40 mM sucrose. The level of inhibition was influenced by the order of addition of potassium and drug to the enzyme. Taken together, these studies indicate that inhibition by A80915A is dependent on the conformation of gastric (H(+)-K+)-ATPase and that potassium slows the rate of inhibition by converting the enzyme to a conformation where the drug binding site is not as accessible. The mode of action of A80915A is distinct from that of two well characterized proton pump inhibitors, omeprazole and SCH 28080.
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PMID:Studies on the mechanism of action of A80915A, a semi-naphthoquinone natural product, as an inhibitor of gastric (H(+)-K+)-ATPase. 168 72

The yeast Saccharomyces cerevisiae was investigated as an in vivo protein expression system for mammalian Na,K-ATPase. Unlike animal cells, yeast cells lack endogenous Na,K-ATPase. Expression of high affinity ouabain binding sites, ouabain-sensitive ATPase activity, or ouabain-sensitive p-nitrophenylphosphatase activity in membrane fractions of yeast cells was observed to require the expression of both alpha subunit and beta subunit polypeptides of Na,K-ATPase in the same cell. High affinity ouabain binding sites are also expressed at the cell surface of intact yeast cells containing both the alpha subunit and the beta subunit of Na,K-ATPase. These observations demonstrate that both the alpha subunit and the beta subunit of Na,K-ATPase are required for the expression of functional Na,K-ATPase activity and that yeast cells can correctly assemble this oligomeric membrane protein and transport it to the cell surface.
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PMID:Synthesis and assembly of functional mammalian Na,K-ATPase in yeast. 168 21

The effect of phospholipids was tested on the p-nitrophenylphosphatase activity of the Ca2+ pump. Acidic phospholipids like phosphatidylserine and phosphatidylinositol inhibited the phosphatase activity, while neutral phospholipids like phosphatidylcholine did not. This result contrasts sharply with the known activating effect of acidic phospholipids on the Ca2(+)-ATPase activity of the pump. It is known that the phosphatase activity of the Ca2+ pump can be elicited either by calmodulin and Ca2+ or by ATP and Ca2+. Unlike calmodulin, acidic phospholipids failed to stimulate the phosphatase activity. Furthermore, calmodulin-activated phosphatase was completely inhibited by acidic phospholipids. Maximal inhibition of the ATP-activated phosphatase was only 70%. Inhibition by acidic phospholipids was non-competitive regarding to calmodulin, suggesting that acidic phospholipids and calmodulin do not bind to the same domain of the pump. The presence of Ca2+ was essential for the inhibition, and the apparent affinity for Ca2+ for this effect was increased by acidic phospholipids. Results are consistent with the idea that acidic phospholipids stabilize an enzyme-Ca complex lacking phosphatase activity.
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PMID:Inhibition of the phosphatase activity of the red cell membrane Ca2+ pump by acidic phospholipids. 184 98

The impact of low level lead exposure on human central nervous system function is a major public health concern. This study addresses the inhibition of the cation pump enzyme Na, K-ATPase by low level lead. Human brain tissue was obtained at autopsy and frozen until use. Brain homogenates were preincubated with PbCl2 for 20 min at 0 degrees C. Inhibition of K-paranitrophenylphosphatase (pNPPase), a measure of the dephosphorylation step of Na,K-ATPase, reached steady state within 10 min. K-pNPPase activity, expressed (mean +/- SEM) as a percentage of control (45.2 +/- 2.7 nmol/mg/min), fell to 96.3 +/- 0.9% at 0.25 uM [PbCl2] to 82.0 +/- 1.6% at 2.5 uM [PbCl2] in homogenates prepared from normal brain. Similar results were obtained with homogenates prepared from brains of patients with a history of alcohol abuse and of those with other miscellaneous conditions. Since the mean blood level of lead in the United States has ranged recently from 9.2 to 16.0 ug/dl (0.44 to 0.77 uM), these results indicate that current in vivo levels of lead exposure may impair important human brain function.
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PMID:Low level lead inhibits the human brain cation pump. 185 20

K+ deficiency has been linked to a loss of K+ from muscle associated with a decrease in ouabain binding and K(+)-dependent phosphatase activity. This study aimed to quantitate the Na(+)-K(+)-ATPase alpha- and beta-isoform-specific responses to hypokalemia in vivo in heart, skeletal muscle, and brain at pre- and posttranslational levels. Two-week dietary K+ restriction resulted in decreases in alpha 2-mRNA in heart and skeletal muscle to 0.60 and 0.65, and in alpha 2-protein abundance to 0.38 and 0.18 of control, respectively. The decrease in alpha 2-protein was greater than the decrease in mRNA in both tissues, suggesting translational and/or posttranslational mechanism(s) of regulation as well as pretranslational regulation in response to hypokalemia. K(+)-dependent p-nitrophenyl phosphatase (pNPPase) activity decreased in heart and skeletal muscle to 0.67 and 0.58, respectively. There were no changes in alpha 1-. or beta-mRNA or protein levels in skeletal muscle or heart. In brain, there was a similar pattern of regulation. While brain alpha 2-mRNA did not change in hypokalemia, protein levels decreased to 0.72 of control. In conclusion, hypokalemia is associated with a large decrease in expression of the alpha 2-isoform of Na(+)-K(+)-ATPase. These results support the hypothesis that in skeletal and heart muscle hypokalemia induces a decrease in Na(+)-K(+)-ATPase activity (measured as K(+)-dependent pNPPase activity) by specifically decreasing the expression of the alpha 2-isoform of Na(+)-K(+)-ATPase.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Hypokalemia decreases Na(+)-K(+)-ATPase alpha 2- but not alpha 1-isoform abundance in heart, muscle, and brain. 185 10

The localization of an ouabain-sensitive potassium-dependent p-nitrophenylphosphatase part of the Na+,K(+)-ATPase complex in the white rat's brain has been studied at the ultrastructural level. The physiological pH of incubation medium highly increases the specificity of ultracytochemical enzyme demonstration. The main characteristics of the enzymatic p-NPP hydrolysis used for this methodological technique are discussed.
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PMID:[An electron microscopic study of the localization of the activity of the ouabain-sensitive, potassium-dependent p-nitrophenylphosphatase component of the Na, K-ATPase complex in the rat brain]. 196 42

Comparison of properties of fragmented sarcoplasmic reticulum samples isolated by several methods is reported. It was found that the protein composition does not differ significantly in samples which were or were not washed with 0.6 M KCl when isolated. In the case of samples washed with KCl solution the Zn concentration, the Ca/Mg ratio (determined from experimental data), acetylcholinesterase and superoxide dismutase activities were higher whereas Ca+Mg-activated ATPase and p-nitrophenylphosphatase activities were lower than those of samples which were not washed with 0.6 M KCl. In the latter samples the amount of SH-groups and the reactivity of fast SH-s are higher in Ca+EGTA containing media than in media containing only EGTA. In contrast in the case of samples washed with KCl solution the results are the opposite. In conclusion, washing of FSR with 0.6 M KCl alters the metal composition, enzymatic properties, SH-group reactivity and as a result of these probably the conformation of the protein samples, as well.
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PMID:Enzymatic properties, metal composition and SH-group reactivity of fragmented sarcoplasmic reticulum isolated from rabbit skeletal muscle. 196 46

Two chalcone derivatives, xanthoangelol (1) and 4-hydroxyderricin (II) isolated from Angelica keiskei Koidzumi, inhibited pig gastric H+, K(+)-ATPase with IC50 values of 1.8 and 3.3 microM, respectively. The inhibition by I or II was competitive with respect to ATP and was non-competitive with respect to K+ I and II also inhibited K+, stimulated p-nitrophenyl phosphatase, with IC50 values of 1.3 and 3.5 microM, respectively. Proton transport in-vitro was inhibited by I or II, in a dose-dependent manner, 1 at 100 mg kg-1, i.p. significantly inhibited acid secretion and the formation of stress-induced gastric lesions. These results suggest that the antisecretory effect of 1 is due to the inhibition of gastric H+, K(+)-ATPase.
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PMID:Inhibition of gastric H+, K(+)-ATPase by chalcone derivatives, xanthoangelol and 4-hydroxyderricin, from Angelica keiskei Koidzumi. 198 46

Thirty-three different flavonoids were screened for their ability to influence ATP-dependent Ca2+ uptake by rat liver plasma membrane vesicles. Nine of the flavonoids, at a concentration of 100 microM inhibited Ca2+ uptake by more than 20%. The remaining 24 flavonoids exhibited little or no effect. The relative order of potency of the more biologically active flavonoids was myricetin greater than butein greater than phloretin = luteolin greater than eriodictyol = silybin. Myricitrin and phloridzin, the glycosides of myricetin and phloretin, respectively, had no effect. The degree of inhibition caused by myricetin was concentration dependent and was also affected by the preincubation time. After 10 min of preincubation, 52 microM myricetin lowered the initial rate of 45Ca uptake by 50%. The inhibition by myricetin was non-competitive with respect to Mg-ATP and of a mixed type with respect to Ca2+. At a concentration of 100 microM, myricetin had no effect on several plasma membrane enzymes such as 5'-nucleotidase, alkaline phosphatase and a Ca2(+)-activated ATPase but inhibited K(+)-dependent p-nitrophenyl phosphatase by 83%. The ATP-dependent Ca2+ transport systems located on the plasma membrane or endoplasmic reticulum derived from other tissues were also inhibited by myricetin. Analysis of the structure-activity relationship revealed that lipid solubility and polyhydroxylation particularly at positions 5,7,3' and 4' of the flavonoid ring structure enhanced the ability of the flavonoid to inhibit Ca2+ uptake. The results suggest that inhibition of Ca2+ transport activity probably involves the interaction of the phenolic groups of the flavonoid with the Ca2+ transporting protein.
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PMID:Effect of myricetin and other flavonoids on the liver plasma membrane Ca2+ pump. Kinetics and structure-function relationships. 199 24


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