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 have reported that dopamine (DA) inhibits Na-K-ATPase activity in the cortical collecting duct (CCD) by stimulating the DA1 receptor, and the present study was designed to evaluate the mechanism of this effect. Short-term exposure (15-30 min) of microdissected rat CCD to DA, a DA1 agonist (fenoldopam), vasopressin (AVP), forskolin, or dibutyryl cAMP (dBcAMP), which increase cAMP content by different mechanisms, strongly (approximately 60%) inhibited Na-K-ATPase activity. 2',5'-dideoxyadenosine, an inhibitor of adenylate cyclase, completely blocked Na-K-ATPase inhibition by DA or fenoldopam, and IP20, an inhibitor peptide of cAMP-dependent protein kinase A (PKA), abolished the Na:K pump effect of all the cAMP agonists listed above. To verify whether the mechanism of pump inhibition by agents that increase cell cAMP involves phospholipase A2 (PLA2), we used mepacrine, a PLA2 inhibitor, which also abolished Na-K-ATPase inhibition by DA or fenoldopam, as well as by AVP, forskolin, or dBcAMP. Arachidonic acid (10(-7) - 10(-4) M) inhibited Na-K-ATPase activity in dose-dependent fashion. Corticosterone, which induces lipomodulin, a PLA2 inhibitor protein inactivated by PKA, equally abolished the pump effects of DA, fenoldopam, forskolin, and dBcAMP, suggesting that lipomodulin might act between PKA and PLA2 in cAMP-dependent pump regulation. We conclude that dopamine inhibits Na-K-ATPase activity in the CCD through a DA1 receptor-mediated cAMP-PKA pathway that involves the stimulation of PLA2 and arachidonic acid release, possibly mediated by inactivation of lipomodulin. This pathway is shared by other agonists that increase cell cAMP and thus stimulate PKA activity.
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PMID:Intracellular signaling in the regulation of renal Na-K-ATPase. I. Role of cyclic AMP and phospholipase A2. 134 27

In agonist-stimulated clonal pituitary gonadotrophs (alpha T3-1 cells), cytoplasmic calcium ([Ca2+]i) exhibited rapid and prominent peak increases, followed by lower, but sustained, elevations for up to 15 min. The [Ca2+]i response to GnRH was rapidly inhibited by prior addition of a potent GnRH antagonist. In the absence of extracellular Ca2+ the initial peak [Ca2+]i response was only slightly decreased, but the prolonged increase in [Ca2+]i was abolished, indicating that the peak is derived largely from intracellular calcium mobilization and the sustained phase from Ca2+ influx. Application of the endoplasmic reticulum Ca(2+)-ATPase blocker thapsigargin caused progressive and dose-dependent elevation of [Ca2+]i and decreased the peak amplitude of the GnRH-induced Ca2+ response. On the other hand, addition of dihydropyridine calcium channel antagonists before or after GnRH treatment prevented or terminated the plateau phase, respectively, consistent with entry of Ca2+ through L-type voltage-sensitive Ca2+ channels (VSCC) as the major Ca2+ influx pathway during GnRH action. The presence of L-type VSCC in alpha T3-1 cells was further indicated by the ability of elevated extracellular K+ levels and the dihydropyridine calcium channel agonist Bay K 8644 to elevate [Ca2+]i in an extracellular calcium-dependent manner. These actions of depolarization and Bay K 8644 were inhibited by nifedipine, with an IC50 of 10 nM. High extracellular K(+)- and GnRH-induced Ca2+ entry was also attenuated by phorbol esters and permeant diacylglycerols, indicating that protein kinase-C exerts inhibitory modulation of VSCC activity. In contrast to normal pituitary gonadotrophs, in which GnRH induces a frequency-modulated oscillatory [Ca2+]i response, single alpha T3-1 cells exhibited a nonoscillatory amplitude-modulated signal during agonist stimulation. The [Ca2+]i responses observed in alpha T3-1 gonadotrophs indicate that the immortalized cells retain functional GnRH receptors and their coupling to the Ca2+ signaling pathway. Ca2+ influx through L-type channels maintains the plateau phase of the [Ca2+]i response during agonist stimulation and is inhibited by activation of protein kinase-C.
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PMID:Gonadotropin-releasing hormone-induced calcium signaling in clonal pituitary gonadotrophs. 137 69

We previously purified RNA polymerase II transcription factor delta from rat liver and found that it has an associated DNA-dependent ATPase (dATPase) activity. In this report, we show that delta is also closely associated with a protein kinase activity that catalyzes phosphorylation of the largest subunit of RNA polymerase II. Kinase activity copurifies with transcription and DNA-dependent ATPase (dATPase) activities when delta is analyzed by anion- and cation-exchange HPLC as well as by sucrose gradient sedimentation, arguing that delta possesses all three activities. Phosphorylation of the largest subunits of both rat and yeast RNA polymerase II is stimulated by DNA, whereas phosphorylation of a synthetic peptide containing multiple copies of the carboxyl-terminal heptapeptide repeat is not. Although both ATP and GTP appear to function as phosphate donors, GTP is utilized less than 10% as well as ATP. These findings suggest that delta may exert its action in transcription at least in part through a mechanism involving phosphorylation of the largest subunit of RNA polymerase II.
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PMID:A carboxyl-terminal-domain kinase associated with RNA polymerase II transcription factor delta from rat liver. 138 28

Endothelin (ET) and GnRH act through specific receptors to promote Ca2+ mobilization and influx pathways in pituitary gonadotrophs. In the present study cytoplasmic calcium ([Ca2+]i) and secretory responses to these two agonists are compared. In single gonadotrophs, low concentrations of both agonists cause oscillatory [Ca2+]i responses after a latent period. Such responses usually consist of discrete transients arising from the normal resting level, but are sometimes super-imposed on an elevated basal calcium level. At high doses, ET-1 and GnRH induce biphasic responses, composed of a spike phase followed by a plateau that often shows high frequency and low amplitude Ca2+ transients. The duration of the latent period and the frequency of the subsequent oscillations are correlated, and both are dependent on agonist concentration. The frequencies and amplitudes of Ca2+ spiking are also interrelated; increases in frequency are followed by more rapid decreases in the amplitude of the Ca2+ transients. After K(+)-induced depolarization, gonadotrophs retain their oscillatory Ca2+ responses to ET-1 and GnRH, with the same frequency as controls. Activation of protein kinase-C by phorbol esters does not alter the frequency of ET-induced Ca2+ transients, but significantly reduces their amplitudes. In contrast, treatment with nanomolar concentrations of thapsigargin converts ET-induced oscillations into a biphasic response, suggesting that Ca(2+)-ATPase in the endoplasmic reticulum participates in the oscillatory mechanism. The two agonists differ in their threshold doses and concentration dependence, ET being significantly less potent than GnRH. Also, gonadotrophs stimulated by ET-1 exhibit different post-treatment responsiveness than those exposed to GnRH. While GnRH-treated cells recover their full [Ca2+]i and secretory responses within 30 min as well as normal [Ca2+]i and secretory responses to ET-1, endothelin-treated cells are refractory to further stimulation with ET and exhibit either attenuated or enhanced Ca2+ and LH responses to GnRH, depending on the duration of exposure to ET-1 and the subsequent recovery period. These data indicate that both receptors use the same mechanism(s) for Ca2+ release, but have different capacities to generate, maintain, and reinitiate the Ca2+ signal.
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PMID:Differential actions of endothelin and gonadotropin-releasing hormone in pituitary gonadotrophs. 144 20

The Ca(2+)-ATPase of skeletal sarcoplasmic reticulum was purified and reconstituted in proteoliposomes containing phosphatidylcholine (PC). When reconstitution occurred in the presence of PC and the acidic phospholipids, phosphatidylserine (PS) or phosphatidylinositol phosphate (PIP), the Ca(2+)-uptake and Ca(2+)-ATPase activities were significantly increased (2-3 fold). The highest activation was obtained at a 50:50 molar ratio of PS:PC and at a 10:90 molar ratio of PIP:PC. The skeletal SR Ca(2+)-ATPase, reconstituted into either PC or PC:PS proteoliposomes, was also found to be regulated by exogenous phospholamban (PLB), which is a regulatory protein specific for cardiac, slow-twitch skeletal, and smooth muscles. Inclusion of PLB into the proteoliposomes was associated with significant inhibition of the initial rates of Ca(2+)-uptake, while phosphorylation of PLB by the catalytic subunit of cAMP-dependent protein kinase reversed the inhibitory effects. The effects of PLB on the reconstituted Ca(2+)-ATPase were similar in either PC or PC:PS proteoliposomes, indicating that inclusion of negatively charged phospholipid may not affect the interaction of PLB with the skeletal SR Ca(2+)-ATPase. Regulation of the Ca(2+)-ATPase appeared to involve binding with the hydrophilic portion of phospholamban, as evidenced by crosslinking experiments, using a synthetic peptide which corresponded to amino acids 1-25 of phospholamban. These findings suggest that the fast-twitch isoform of the SR Ca(2+)-ATPase may be also regulated by phospholamban although this regulator is not expressed in fast-twitch skeletal muscles.
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PMID:Regulation of the skeletal sarcoplasmic reticulum Ca(2+)-ATPase by phospholamban and negatively charged phospholipids in reconstituted phospholipid vesicles. 146 Dec 59

Calcium ions have been proposed to serve as important regulatory elements in stimulus-response coupling for phytochrome responses. An important test of this hypothesis will be to identify specific targets of calcium action that are required for some growth or development process induced by the photoactivated form of phytochrome (Pfr). Initial studies have revealed that there are at least two enzymes in pea nuclei that are stimulated by Pfr in a Ca(2+)-dependent fashion, a calmodulin-regulated nucleoside triphosphatase and a calmodulin-independent but Ca(2+)-dependent protein kinase. The nucleoside triphosphatase appears to be associated with the nuclear envelope, while the protein kinase co-purifies with a nuclear fraction highly enriched for chromatin. This short review summarizes the latest findings on these enzymes and relates them to what is known about Pfr-regulated nuclear metabolism.
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PMID:Calcium-regulated nuclear enzymes: potential mediators of phytochrome-induced changes in nuclear metabolism? 147 26

We studied changes in myofibrillar function and protein profiles after complete global ischemia with anoxia in rat hearts. Hearts were exposed to global ischemia and anoxia (CGI) for 30 or 60 minutes at 37 degrees C, and myofibrils were prepared for measurement of Ca(2+)-dependent Mg(2+)-ATPase activity at pH 7.0 and 6.5. Hearts incubated in cold saline (1 +/- 1 degrees C) and nonincubated hearts served as controls. Maximum ATPase activity was unchanged at pH 7.0 and pH 6.5 in myofibrils from hearts treated with 30 or 60 minutes of CGI. At pH 7.0, the Hill coefficient, which is an index of cooperative interactions among thin-filament proteins, was unchanged after 30 minutes of CGI but was significantly increased after 60 minutes of CGI. A similar trend for increased cooperativity was observed when myofibrillar ATPase activity was measured at pH 6.5 in myofibrils from rat hearts made ischemic for 30 or 60 minutes. Both 30 and 60 minutes of CGI resulted in increased pCa50 values (half-maximally activating free [Ca2+]) at pH 7.0 and pH 6.5. Densitometric analysis of myofibrillar proteins separated with sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that troponin I and troponin T were degraded during 60 minutes of CGI. Two new protein bands appearing in ischemia-treated myofibrils were identified as partially degraded troponin I and troponin T with Western blots. The troponin I fragment could be phosphorylated by cAMP-dependent protein kinase. In addition, we observed phosphorylation of a protein band that corresponded to myosin light chain-2 in myofibrils from CGI-treated hearts. These results suggest that degradation of thin-filament proteins may contribute to the changes in cooperativity of Ca2+ regulation of ATPase activity observed in the myofibrils from rat hearts exposed to CGI.
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PMID:Alterations in myofibrillar function and protein profiles after complete global ischemia in rat hearts. 153 Nov 86

The human immunodeficiency virus 1 (HIV-1) nef gene encoded by the HIV-1 isolate lymphadenopathy-associated virus type 1 was expressed in Escherichia coli under the control of the tac promoter. The protein is found mainly in the soluble part of the bacterial lysate; a simple two-column purification scheme has been developed allowing isolation of the recombinant protein without using denaturing agents. Analysis of the circular dichroism spectra reveals that the purified protein is folded and has a helix content of 16% and a beta-pleated sheet content of 31%. GTPase activity and binding of guanine nucleotides were measured for Nef and compared with the results obtained under identical experimental conditions for p21rasC, which represents a typical, well-characterized guanine-nucleotide-binding (GNB) protein. Within the limits of error, native Nef does not show GTPase activity and does not bind guanine nucleotides strongly (association constant, Kass less than 5 x 10(3) M-1). An upper limit for the association constant of Nef for ATP was determined by equilibrium dialysis as 5 x 10(3) M-1. Nef can be autophosphorylated by ATP; under the experimental conditions used, 1-2% of the protein become phosphorylated. Correspondingly, our Nef preparation shows a low, but significant, ATPase activity. In conclusion, Nef is not a member of the GNB protein family, but a possible role as a protein kinase cannot be excluded.
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PMID:Expression, purification and biochemical characterisation of the human immunodeficiency virus 1 nef gene product. 153 85

We recently reported that autophosphorylated protein kinase C (PKC) has an intrinsic Ca(2+)- and phospholipid-dependent ATPase activity and that the ATPase and histone kinase activities of PKC have similar metal-ion cofactor requirements and Km,app(ATP) values. We hypothesized that the intrinsic ATPase activity of PKC may represent the bond-breaking step of its protein kinase activity. The rate of the ATPase reaction is several times slower than the histone kinase reaction rate. At subsaturating concentrations, various peptide and protein substrates stimulate the ATPase reaction by as much as 1.5-fold. In contrast, non-phosphorylatable substrate analogs are not stimulatory. These observations support a mechanism of PKC catalysis in which the productive binding of phosphoacceptor substrates enhances the rate of phosphodonor substrate (ATP) hydrolysis at the active site of PKC. However, this mechanism contains an assumption that the ATPase activity of PKC is catalyzed at the active site. In fact, sequence analysis indicates that PKC contains a potential second nucleotide binding site outside of its active site. In this report, we provide a detailed analysis of the relationship between the active site of PKC and the intrinsic ATPase activity of the enzyme. We show that the regulatory and catalytic properties of the ATPase reactions of three PKC isozymes are similar, despite critical differences among the isozymes in their consensus sequences for the potential non-active-site nucleotide binding site in their catalytic domains. We also show that the ATPase and histone kinase reactions of each isozyme have similar Km,app(ATP) values.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The intrinsic ATPase activity of protein kinase C is catalyzed at the active site of the enzyme. 153 19

A nucleoside triphosphatase (NTPase) activity appeared to be associated with a highly purified nuclear preparation from rat cardiac ventricles. Different nucleoside triphosphates (UTP greater than GTP greater than ITP greater than CTP) supported this enzymic activity, which was stimulated by Mg2+ but not by Ca2+. The nuclear NTPase activity could be down regulated by endogenous phosphorylation of a 55,000 Mr protein. Maximal phosphorylation of the 55,000 Mr protein occurred in the presence of Mg(2+)-ATP. Addition of cAMP, cGMP, Ca2+, Ca2+/phospholipid, Ca2+/calmodulin, and catalytic subunit of cAMP-dependent protein kinase was not associated with any further phosphorylation of the 55,000 Mr protein. However, in the presence of Ca2+/calmodulin or the catalytic subunit of the cAMP-dependent protein kinase additional proteins became phosphorylated, but these had no effect on the Mg(2+)-NTPase activity. These results indicate that a protein with Mr 55,000 may be involved in the regulation the Mg(2+)-NTPase activity associated with rat cardiac nuclei.
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PMID:Regulation of rat cardiac nuclei-associated Mg(2+)-NTPase by phosphorylation. 165 81


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