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)

The relationship between the 22-24 kDa cyclic AMP (cAMP)-dependent phosphoprotein previously described as being involved in the regulation of human platelet membrane Ca2+ transport and a GTP-binding protein of low molecular mass (ras-like protein) was investigated. After isolation of plasma membranes and intracellular membranes, it was found that guanosine 5'-[gamma-thio]triphosphate (GTP[S]) bound to plasma membrane proteins ranging in molecular mass from 22 to 29 kDa, but not to intracellular membranes. The major GTP-binding protein appeared as a 24 kDa protein under reduced conditions and a 22 kDa protein under non-reduced conditions. A similar membrane location and electrophoretic mobility were found for both the cAMP phosphoprotein and the protein recognized by a specific anti-rap1 antibody. The identity between the cAMP phosphoprotein and the rap1 GTP-binding protein was further examined by studying the functional effect of GTP on plasma membrane Ca2+ transport. A maximal GTP[S] concentration of 40 microM was found to: (1) inhibit to the same degree (40%) both Ca(2+)-ATPase activity and the Ca2+ transport function mediated by the Ca(2+)-ATPase; (2) inhibit the phosphorylation of the 22-24 kDa protein by the catalytic subunit of the cAMP-dependent protein kinase (C.Sub.); and (3) abolish the stimulation of Ca2+ uptake induced by C.Sub. It is concluded that the platelet cAMP phosphoprotein is indeed the rap1 GTP-binding protein, and that it regulates plasma membrane Ca2+ transport, thus providing evidence for a new role of a ras-related protein.
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PMID:Evidence for a role of rap1 protein in the regulation of human platelet Ca2+ fluxes. 131 May 90

The effects of the cholinergic agonist carbachol (Cch) and guanine nucleotides on the Na,K-ATPase and K-dependent p-nitrophenylphosphatase (K-p-NPPase) activities in rabbit and dog myocardial sarcolemma vesicles in the presence of the pore-forming antibiotic alamethicin (20 micrograms/ml), was studied. Cch (0.01-100 microM) inhibited the both enzymatic activities by 40-45% (IC50 = 0.3-0.5 microM) only after addition of GTP (50 microM) or its analogs: GTP gamma S (0.1-1.0 microM) and Gpp(NH)p (10 microM). The muscarinic acetylcholine receptor (mAchR) antagonist atropine (10 microM) blocked the effect of Cch. GTP gamma S alone produced a concentration-dependent decrease in the both Na,K-ATPase and K-p-NPPase activities by 40-45% (IC50 = 1-2 microM) with a lag period of about 3 minutes; this lag disappeared in the presence of the agonist. The GDP analog GDP beta S (0.01-100 microM) neither affected these activities nor promoted the inhibiting effect of Cch. Pretreatment of sarcolemmal vesicles with 20 micrograms/ml of pertussis toxin in the presence of 100 microM NAD abolished the inhibiting effect of Cch on the Na,K-ATPase and phosphatase activities. Under these conditions pertussis toxin catalyzed the ADP-ribosylation of alpha-subunits of the inhibitory GTP-binding protein (G1) which were identified immunochemically as alpha i2, alpha i3 and, possibly, alpha i1. The data obtained testify to the involvement of G1 in the mAchR-mediated inhibition of myocardial sarcolemmal Na,K-ATPase as well as in the signal transduction from the receptor to the enzyme.
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PMID:[The role of a GTP-binding protein in coupling of a muscarinic cholinergic receptor and Na,K-ATPase in myocardial sarcolemma]. 132 37

Angiotensin II (AngII) is a potent regulator of electrolyte transport with biphasic effects on salt and HCO3-resorption in proximal tubule epithelia (PCT). In cultured PCT cells, pM to nM AngII activates a GTP-binding protein to inhibit cAMP formation and thus releases inhibition of apical Na/H exchange. Phospholipase A2 is activated by nM to microM AngII releasing arachidonate which is metabolized by a novel P450 epoxygenase to form 5,6-epoxy-eicosatrienoic acid (5,6-EET). 5,6-EET and nM apical AngII cause dihydropyridine-sensitive Ca2+ influx from the extracellular space, inhibition of apical-to-basolateral Na flux, and decrease in epithelial monolayer short circuit current. 5,6-EET also inhibits Na/K-ATPase by 50%. This P450 epoxygenase is physiologically important in the AngII-signaling system because the P450 inhibitor ketoconazole blocks AngII effects while potentiating exogenous 5,6-EET effects. Finally, these AngII-mediated signaling systems are polarized in the PCT with pM basolateral AngII inhibiting adenylate cyclase and nM apical AngII activating PLA2 and subsequent generation of 5,6-EET.
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PMID:Angiotensin II actions in the rabbit proximal tubule. Angiotensin II mediated signaling mechanisms and electrolyte transport in the rabbit proximal tubule. 170 6

Na, K-ATPase and Mg-ATPase activities were measured in the synaptosomes of the temporal auditory projection area and the frontal association area. Moreover, the effects of carbacholine and serotonin on those activities were investigated. Na, K-ATPase activity in the synaptosomes of the association area was shown to be reliably higher that in the synaptosomes of the projection area (11.02 +/- 0.45 vs 8.40 +/- 0.55 microM Pi/mg of protein hr; P less than 0.05). Mg-ATPase activity was higher in the second case as compared to the first one (11.40 +/- 0.38 vs 9.04 +/- 0.35; p less than 0.05). Carbacholine and serotonin (10(-8)-10(-3) M) were found to induce equal inhibition of Na, K-ATPase activity in the synaptosomes of both cortices (1 max = 25-30%, 1C50 = 0.2-0.3 microM) which is blocked respectively with atropine (10(-6) M) and methysergide (10(-6) M) and enhanced in presence of GTP (5.10(-5) M). The enzyme activity is also inhibited by the non-hydrolysable guanine nucleotide, GTP gamma S (10(-8)-10(-4) M), in the absence of the antagonists (1 max = 35-40%, 1 C50 = 0.02 microM). In the methysergide-containing medium serotonin exerts a dose-dependent stimulatory effect on Na, K-ATPase which is more pronounced in the synaptosomes of the association area (A max = 25%, A C50 = 0.05 microM). Mg-ATPase activity of membrane preparations is liable to be stimulated by both serotonin and carbacholine, stimulation being more pronounced in the synaptosomes of the association cortex as well (A max = 35%, A C50 = 0.2-0.3 microM). This effect is insensitive either to the antagonists of the corresponding receptors or to GTP. GTP gamma S does not cause alterations in the enzymatic activity. Na, K-ATPase is suggested to be coupled to muscarine and serotonin receptors in the synaptic membranes of both projection and association cortical areas via a GTP-binding protein. At the same time, the agonists of receptors mentioned above are presumably also capable to effect Mg-ATPase activity by the receptor-independent way.
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PMID:[Effect of carbacholine and serotonin on the ATPase activity in synaptosomes of the projection and association areas of the feline cerebral cortex]. 185 44

We have reported recently that prostaglandin E2 (PGE2) stimulated phosphoinositide metabolism in bovine adrenal chromaffin cells and that PGE2 and ouabain, an inhibitor of Na+, K(+)-ATPase, synergistically induced a gradual secretion of catecholamines from the cells. Here we examined the involvement of a GTP-binding protein(s) in PGE receptor-induced responses by using NaF. In the presence of Ca2+ in the medium, NaF stimulated the formation of all three inositol phosphates, i.e., inositol monophosphate, bisphosphate, and trisphosphate, linearly over 30 min in a dose-dependent manner (15-30 mM). This effect on phosphoinositide metabolism was accompanied by an increase in cytosolic free Ca2+. NaF also induced catecholamine release from chromaffin cells, and the dependency of stimulation of the release on NaF concentration was well correlated with those of NaF-enhanced inositol phosphate formation and increase in cytosolic free Ca2+. Although the effect of NaF on PGE2-induced catecholamine release in the presence of ouabain was additive at concentrations below 20 mM, there was no additive effect at 25 mM NaF. Furthermore, the time course of catecholamine release stimulated by 20 mM NaF in the presence of ouabain was quite similar to that by 1 microM PGE2, and both stimulations were markedly inhibited by amiloride, with half-maximal inhibition at 10 microM. Pretreatment of the cells with pertussis toxin did not prevent, but rather enhanced, PGE2-induced catecholamine release over the range of concentrations examined. These results demonstrate that NaF mimics the effect of PGE2 on catecholamine release from chromaffin cells and suggest that PGE2-evoked catecholamine release may be mediated by the stimulation of phosphoinositide metabolism through a putative GTP-binding protein insensitive to pertussis toxin.
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PMID:Sodium fluoride mimics the effect of prostaglandin E2 on catecholamine release from bovine adrenal chromaffin cells. 189 68

The role of 48-kDa protein in visual transduction remains unresolved. Two hypotheses for its role in quenching the light activation of cyclic GMP cascade suggest that the protein binds to either phosphodiesterase or phosphorylated rhodopsin. Since the protein is also reported to bind ATP, we anticipated that the protein may have ATP hydrolyzing activity, and in analogy with the GTP-binding protein of the rod outer segments, such activity may be greatly enhanced by the elements of transduction cyclic GMP cascade, permitting the protein to function cyclically as GTP-binding protein does. We found that purified 48-kDa protein hydrolyzes ATP but at a slow rate of 0.04-0.05 per min. The Km for ATP is about 45-65 microM. The activity is inhibited noncompetitively by ADP with a Ki of about 50 microM. The ATPase activity of 48-kDa protein is not affected by rhodopsin, bleached rhodopsin, phosphorylated rhodopsin, unactivated cyclic GMP phosphodiesterase, or phosphodiesterase (PDE) activated by GMP PNP-bound G-protein. These data show that although 48-kDa protein has ATPase activity, lack of regulation of this activity by the elements of visual transduction makes it unlikely for this activity to have a role in quenching the light activation of cyclic GMP cascade.
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PMID:Photoreceptor rod outer segment 48-kDa protein has ATPase activity. 215 Jul 55

GTP-binding proteins were studied in synaptic vesicles prepared from bovine brain by differential centrifugation and separated further from plasma membranes using gel permeation chromatography. Following separation by SDS-PAGE of proteins from the different fractions, and transfer to nitrocellulose sheets, the presence and localization of low-molecular-mass GTP-binding proteins were assessed by [alpha-32 P]GTP binding. The vesicle-membrane fraction (SV) was enriched in synaptophysin (p38, a synaptic vesicle marker) and contained low-molecular-mass GTP-binding proteins; these consisted of a major 27 kDa protein and minor components (Mr 26 and 24 kDa) which were trypsin-sensitive and immunologically distinguishable from ras p21 protein. GTP-binding proteins of low molecular mass, but displaying less sensitivity to trypsin, were also found in the plasma membrane fraction (PM; enriched in Na+/K(+)-ATPase). In addition, the PM fraction contained GTP-binding proteins with higher Mr (Gi alpha and G0 alpha), together with another GTP-binding protein, ras p21. Putative function(s) of these GTP-binding proteins with low mass are discussed.
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PMID:Identification and localization of low-molecular-mass GTP-binding proteins associated with synaptic vesicles and other membranes. 216 11

The short term regulation of the activity of the Na,K-pump (Na+,K(+)-ATPase) is just beginning to be understood. By using single microdissected proximal tubule segments (PCT) (permeabilized in order to clamp Na entry), it was possible to study regulation of Na+,K(+)-ATPase activity in its own environment and in a well defined cell population. The Na+,K(+)-ATPase activity can be regulated over a short term via guanidine triphosphate (GTP) dependent regulatory proteins. However the guanidine proteins are not directly coupled to the Na,K-pump and the mechanism involves the activation of complex intracellular signalling system. Locally produced dopamine induces a dose dependent inhibition of Na+,K+ ATPase activity. This inhibition is mediated by a complex mechanism that requires the activation of both membrane dopamine receptors, DA-1 and DA-2. It involves the activation of a pertussis toxin sensitive GTP-binding protein and activation of protein kinase C. A DA-2 agonist only inhibits Na+,K(+)-ATPase activity when it is incubated together with dibutyryl cAMP or Forskolin. We have therefore concluded that an increase in cellular cAMP levels plays a permissive role for DA-2 inhibition of Na+,K(+)-ATPase activity. A fully differentiated cell is required for dopamine inhibition of Na+,K(+)-ATPase activity. An abnormal regulation of proximal tubule Na+,K(+)-ATPase activity might be of importance in the pathogenesis of certain types of hypertension.
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PMID:Short-term regulation of Na+,K(+)-ATPase activity by dopamine. 216 34

The localization of GTP-binding protein (G-protein) subunits, Go alpha, Gi2 alpha and beta, in subcellular fractions of rat cerebral cortex was determined by means of immunoassays specific for the respective subunits. High concentrations of all three subunits were observed in both crude mitochondrial and microsomal fractions. Muscarinic cholinergic receptors were also densely localized in these fractions. Then the crude mitochondrial and microsomal fractions were subfractionated by sucrose density gradient centrifugation. Each fraction obtained was evaluated morphologically by electron microscopy and biochemically by determination of membrane markers. The crude mitochondrial fraction was subfractionated into myelin, synaptic plasma membrane, and mitochondrial fractions. All the G-protein subunits examined and muscarinic receptors were exclusively localized in the synaptic plasma membrane fraction. Among the submicrosomal fractions, the heavy smooth-surfaced microsomal fraction showed the highest concentrations of all G-protein subunits and receptors, while the rough-surfaced microsomal fraction contained low amounts of them. The heavy smooth-surfaced microsomal fraction also contained high specific activity of (Na(+)-K+)-ATPase, a marker of the plasma membrane. These results indicated that the Go alpha, Gi2 alpha and beta subunits are mainly localized in the plasma membrane in the brain.
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PMID:Subcellular distribution of GTP-binding proteins, Go and Gi2, in rat cerebral cortex. 216 70

The effects of the cholinergic agonist carbachol on ouabain-sensitive K(+)-activated 4-nitrophenylphosphatase (K(+)-O2NPhPase) activity of rabbit and pig ventricular sarcolemma were examined. Carbachol (0.01-1000 microM) alone had no effect on K(+)-O2NPase. However, in the presence of GTP (100 microM) or its analog guanosine 5'-[gamma-thio]triphosphate (GTP[S], 1 microM) the agonist reduced this enzymatic activity (IC50 = 0.3 microM) by about 45% in a concentration-dependent manner. The GTP[S]-dependent effect of carbachol was blocked by 10 microM atropine, an antagonist of muscarinic acetylcholine receptor (mAcChoR). In the presence of micromolar concentrations of ATP or the GDP analog guanosine 5'-[beta-thio]diphosphate, carbachol did not change sarcolemmal K(+)-O2NPhPase activity. GTP[S] alone reduced this activity (IC50 = 2 microM) by about 40% in a concentration-dependent manner with a lag period of about 3 min. This lag disappeared in the presence of carbachol. Treatment of sarcolemmal membranes with 20 micrograms/ml pertussis toxin, which catalyzed ADP-ribosylation of the 40-41-kDa alpha-subunits of inhibitory GTP-binding protein (Gi), abolished the GTP[S]-promoted inhibitory effect of carbachol. Immunochemically, these alpha-subunits were identified as alpha 12- and alpha i3-subunits. It is suggested that the carbachol-induced inhibition of ouabain-sensitive K(+)-O2NPhPase activity of mammalian myocardial sarcolemma is a result of a negative coupling between mAcChoR and Na+/K(+)-ATPase via Gi protein.
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PMID:Involvement of pertussis-toxin-sensitive G protein in muscarinic-receptor-mediated inhibition of K(+)-activated 4-nitrophenylphosphatase activity of cardiac sarcolemma. 217 73


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