Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P20020 (adenosine triphosphatase)
 3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previously, we have shown that okadaic acid (OA), isolated from black sponge (Halichondria okadai) causes contraction even in the absence of Ca++ in the saponin-permealized taenia isolated from guinea pig cecum. In the present study, mechanism of action of OA was examined using native actomyosin extracted from chicken gizzard smooth muscle. In the absence of Ca++, OA (0.1-1 microM) induced superprecipitation and increased the Mg++-adenosine triphosphatase activity. The OA-induced superprecipitation was enhanced by Ca++ at a concentration (greater than 0.1 microM) which did not activate the calmodulin-dependent myosin light chain (MLC) kinase. The effect of OA was not affected by the calmodulin inhibitor, trifluoperazine, at a concentration (100 microM) needed to inhibit the Ca++-induced response, but was inhibited markedly by the nonselective kinase inhibitors, amiloride (1 mM) and K-252a (5 microM). The OA-induced superprecipitation in the absence of Ca++ was accompanied by phosphorylation of the 20 K dalton MLC, which also was enhanced by low concentration of Ca++ (greater than 0.1 microM). OA did not change the phosphatase activity which dephosphorylates the phosphorylated MLC. An activator of Ca++- and phospholipid-dependent protein kinase, 12-O-tetradecanoylphorbol 13-acetate (1 microM), did not modulate superprecipitation or phosphorylation of MLC in the presence and absence of OA. Furthermore, inhibitors of Ca++ and phospholipid-dependent protein kinase, 1-(5-isoquinoline-sulfonyl)-2-methylpiperazine dihydrochloride (400 microM) and polymyxin B (100 micrograms/ml), affected neither superprecipitation nor phosphorylation of MLC induced by OA. With a reconstituted system containing purified myosin and MLC kinase, OA induced only slight phosphorylation of MLC.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Calcium-independent phosphorylation of smooth muscle myosin light chain by okadaic acid isolated from black sponge (Halichondria okadai). 282 58

Specific atrial natriuretic factor (ANF) analogues have been found to have inhibitory activity in vitro in a calmodulin-dependent, human red blood cell membrane Ca2+-adenosine triphosphatase (ATPase) model. Studied at 10(-8) to 10(-6) M concentrations, atriopeptin I (residues 127-147 of rat prepro-ANF sequence) and atriopeptin III (residues 127-150) progressively inhibited Ca2+-ATPase activity by up to 20% (p less than 0.001). This degree of inhibition was consistent with activities of other (calmodulin-independent) enzyme inhibitors in this model. Therefore, the C-terminal Phe-Arg-Tyr sequence (residues 148-150) is unnecessary for atriopeptin action on Ca2+-ATPase. Human and rat atrial peptides with amino acids 123-150 were inactive, indicating that the 123-126 sequence (Ser-Leu-Arg-Arg) must be cleaved to activate atriopeptins in this system. Human ANF fragment 129-150 also had no effect on Ca2+-ATPase, defining the importance of residues 127-128 (Ser-Ser) proximal to the disulfide bridge (joining 129 to 145). The addition of purified calmodulin to red blood cell membranes in the presence of inhibitory ANF did not restore Ca2+-ATPase activity to normal levels, indicating that the ANF effect on this enzyme is calmodulin-independent. Atriopeptin I and atriopeptin III had no effect on red blood cell Na+, K+-ATPase activity in vitro. Thus, the structure-activity relationships of ANF analogues in this novel human cell membrane model are highly specific. Although the inhibitory action of ANF analogues on Ca2+-ATPase, a calcium pump-associated enzyme, may be unique to the red blood cell, the calcium dependence of the gluconeogenic effects of ANF in the kidney would be supported by inhibition of this ATPase.
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PMID:Analogue-specific action in vitro of atrial natriuretic factor on human red blood cell Ca2+-ATPase activity. 284 69

Native thin filaments were extracted from rabbit uterus by the procedure of Marston and Smith. The protein content was actin, tropomyosin, and caldesmon in molar ratios of 1:0.2:0.03. Some filamin, myosin, and calcium-binding protein were also present. The thin filaments activated skeletal or smooth muscle myosin magnesium adenosine triphosphatase at least 30-fold. Activation was regulated by Ca2+; maximum observed Ca2+ sensitivity was greater than 10 times. The thin filaments were dismantled into component proteins by the method of Smith and Marston. Actin and actin-tropomyosin-activated myosin magnesium adenosine triphosphatase, but the activation was not Ca2+-regulated. Added caldesmon inhibited adenosine triphosphatase activation by as much as 80%, with 50% inhibition at 1 caldesmon per 50 actin. Caldesmon inhibition was not Ca2+ dependent, but inhibition could be reversed by further addition of Ca2+ and calmodulin. It is concluded that the thin filaments of uterine smooth muscle are Ca2+ regulated and that this regulatory system could be involved in control of uterine smooth muscle contractility. A mechanism for thin filament regulation, mediated by caldesmon, is proposed.
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PMID:Calcium ion-dependent regulation of uterine smooth muscle thin filaments by caldesmon. 291 89

Several operationally defined adenosine triphosphatase (ATPase) activities were determined in vitro in red blood cell lysates of normotensive or hypertensive humans: Mg2+-ATPase, Na+,K+-ATPase, and Ca2+ pump ATPase, the latter in the calmodulin-activated and basal states. Basal Ca2+ pump ATPase was defined as the Ca2+-activated ATPase resistant to 10(-4) M trifluoperazine. Subjects were part of a double-blind study in which treatment was divided into several phases: baseline (4 weeks), placebo or calcium (1 g elemental calcium/day, 8 weeks), placebo washout (4 weeks), placebo or calcium (1 g elemental calcium/day, 8 weeks). Irrespective of the phase of treatment, the basal Ca2+ pump ATPase activity in red blood cell lysates of 36 hypertensive subjects was significantly less than that in lysates from 18 normotensive subjects. Other ATPase activities did not differ significantly, although all ATPases tended to be decreased in hypertension. The data are consistent with previous reports of altered membrane Ca2+ binding and transport in hypertension, but the precise changes are not elucidated.
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PMID:Decreased calcium pump adenosine triphosphatase in red blood cells of hypertensive subjects. 294 85

The effects of lead (Pb) on the calmodulin activation of human red blood cell membrane calcium-dependent adenosine triphosphatase (Ca-ATPase) were studied in vitro. It was not possible to exclude EGTA from the hemolyzing buffer and retain Ca-ATPase activity and therefore exact concentrations of Pb in the incubation are not known. Nonetheless, nanomolar concentrations of Pb stimulated Ca-ATPase with or without exogenous calmodulin and none of the Pb concentrations tested (1 nM-100 microM) interfered with the calmodulin stimulation of the enzyme. High concentrations of Pb (greater than 10 microM) inhibited Ca-ATPase activity. It is possible that low concentrations of Pb can interfere with calcium dependent processes but the calcium-regulatory protein, calmodulin, is not susceptible to interference by Pb under the conditions used here.
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PMID:Lead does not affect calmodulin-induced activation of calcium-dependent adenosine triphosphatase in human red blood cell membranes. 294 23

Human red cell membrane Ca2+-stimulatable, Mg2+-dependent adenosine triphosphatase (Ca2+-ATPase) activity and its response to thyroid hormone have been studied following exposure of membranes in vitro to specific long-chain fatty acids. Basal enzyme activity (no added thyroid hormone) was significantly decreased by additions of 10(-9)-10(-4) M-stearic (18:0) and oleic (18:1 cis-9) acids. Methyl oleate and elaidic (18:1 trans-9), palmitic (16:0) and lauric (12:0) acids at 10(-6) and 10(-4) M were not inhibitory, nor were arachidonic (20:4) and linolenic (18:3) acids. Myristic acid (14:0) was inhibitory only at 10(-4) M. Thus, chain length of 18 carbon atoms and anionic charge were the principal determinants of inhibitory activity. Introduction of a cis-9 double bond (oleic acid) did not alter the inhibitory activity of the 18-carbon moiety (stearic acid), but the trans-9 elaidic acid did not cause enzyme inhibition. While the predominant effect of fatty acids on erythrocyte Ca2+-ATPase in situ is inhibition of basal activity, elaidic, linoleic (18:2) and palmitoleic (16:1) acids at 10(-6) and 10(-4) M stimulated the enzyme. Methyl elaidate was not stimulatory. These structure-activity relationships differ from those described for fatty acids and purified red cell Ca2+-ATPase reconstituted in liposomes. Thyroid hormone stimulation of Ca2+-ATPase was significantly decreased by stearic and oleic acids (10(-9)-10(-4) M), but also by elaidic, linoleic, palmitoleic and myristic acids. Arachidonic, palmitic and lauric acids were ineffective, as were the methyl esters of oleic and elaidic acids. Thus, inhibition of the iodothyronine effect on Ca2+-ATPase by fatty acids has similar, but not identical, structure-activity relationships to those for basal enzyme activity. To examine mechanisms for these fatty acid effects, we studied the action of oleic and stearic acids on responsiveness of the enzyme to purified calmodulin, the Ca2+-binding activator protein for Ca2+-ATPase. Oleic and stearic acids (10(-9)-10(-4) M) progressively inhibited, but did not abolish, enzyme stimulation by calmodulin (10(-9) M). Double-reciprocal analysis of the effect of oleic acid on calmodulin stimulation indicated noncompetitive inhibition. Addition of calmodulin to membranes in the presence of equimolar oleic acid restored basal enzyme activity. Oleic acid also reduced 125I-calmodulin binding to membranes, but had no effect on the binding of [125I]T4 by ghosts. The mechanism of the decrease by long chain fatty acids of Ca2+-ATPase activity in situ in human red cell ghosts thus is calmodulin-dependent and involves reduction in membrane binding of calmodulin.
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PMID:Action of long-chain fatty acids in vitro on Ca2+-stimulatable, Mg2+-dependent ATPase activity in human red cell membranes. 296 20

In the present in-vitro study we investigated the possible role of the calmodulin-antagonistic drugs loperamide and calmidazolium in the regulation of transepithelial Ca2+ transport of human duodenum. Brush border membrane vesicles and basolateral membrane vesicles were simultaneously prepared from surgically resected pieces of morphologically intact human duodenum with a modified Percoll-gradient centrifugation method. Brush border and basolateral membrane vesicles were characterized using enzyme marker analysis and electron microscopy: alkaline phosphatase was enriched 20-fold in brush border membrane vesicles, whereas [Na+ + K+]-stimulated adenosine triphosphatase was enriched 15-fold in basolateral membrane vesicles. Calmodulin activity was determined by a specific radioimmunoassay after solubilizing brush border and basolateral membrane vesicles in 1% Triton X-100. In basolateral membrane vesicles, we found no calmodulin activity. In brush border membrane vesicles calmodulin activity was impaired by 50% after pre-incubation with loperamide or calmidazolium. We measured calcium, sodium, D-glucose and D-mannitol uptake with a rapid filtration technique. Before the transport experiments, brush border and basolateral membrane vesicles were pre-incubated with 5 microM loperamide or 5 microM calmidazolium for 60 min at 5 degrees C. In drug-pretreated, brush border membrane vesicles calcium uptake was significantly reduced after 1 min incubation (-25% +/- 5%, P less than 0.05); this effect was completely reversed in the presence of 5 microM calmodulin. In basolateral membrane vesicles, we found two Ca2+ transport systems: (1) Na+/Ca2+ exchange and (2) ATP-dependent Ca2+ transport. In basolateral membrane vesicles loperamide had no effect. Calmidazolium had no effect on Na+/Ca2+ exchange, but significantly inhibited ATP-dependent Ca2+ transport. This effect could not be reversed by calmodulin.
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PMID:Effect of two potent calmodulin antagonists on calcium transport of brush border and basolateral vesicles from human duodenum. 297 85

A newly synthesized compound, N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA-1004), was shown to be a potent inhibitor of two cyclic nucleotide-dependent protein kinases, cyclic GMP-dependent protein kinase and cyclic AMP-dependent protein kinase and the Ki values were 1.4 and 2.3 microM, respectively. HA-1004 relaxed rabbit aortic strips contracted by various agonists and with similar ED50 values. Phenotolamine, propranolol and atropine did not affect this HA-1004-induced relaxation, thereby suggesting that this compound does not act through these membrane receptor associated mechanisms. HA-1004 shifted the dose-response curve for CaCl2 to the right in a competitive manner in depolarized rabbit renal arterial strips. This compound also relaxed the A-23187 and phenylephrine-induced contractions elicited in Ca++-free solution. These findings suggest that HA-1004 exerts its action at the intracellular or submembranal level. This vasodilator has little effect on actomyosin adenosine triphosphatase and Ca++-calmodulin-dependent myosin light chain kinase. Studies using its derivatives with various lengths of alkyl chain (C0-C6) indicated that the potencies of these compounds, as vasorelaxants, correlated well with their potential to inhibit cyclic nucleotide-dependent protein kinase. HA-1004 should be a useful tool for investigating in smooth muscle, regulatory mechanism(s) by second messengers, cyclic AMP and cyclic GMP.
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PMID:Relaxation of vascular smooth muscle by HA-1004, an inhibitor of cyclic nucleotide-dependent protein kinase. 299 36

Calcium initiates smooth muscle contraction by binding to calmodulin and activating the enzyme myosin light chain kinase. The activated form of myosin light chain kinase phosphorylates myosin on the 20,000-dalton light chain and contractile activity ensues. Calcium may also enhance smooth muscle contractile activity by binding directly to myosin, the main component of the thick filament. Recent studies raise the possibility that the calcium-calmodulin complex may also modulate smooth muscle contractile activity by removing the inhibition imposed by caldesmon, a protein that is bound to the thin (i.e., actin-containing) filaments of smooth muscle. In vitro studies have demonstrated that the calcium-activated, phospholipid-dependent kinase, protein kinase C, can phosphorylate smooth muscle myosin at a different site than does myosin light chain kinase and down-regulate its actin-activated magnesium adenosine triphosphatase activity. This raises the possibility that protein kinase C phosphorylation of myosin may play a role in modulating vascular contractile activity in vivo.
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PMID:Effects of calcium on vascular smooth muscle contraction. 302 18

Diabetes mellitus is frequently associated with a primary cardiomyopathy. The mechanisms responsible for this heart disease are not clear, but an alteration in myocardial Ca2+ transport is believed to be involved in its development. Even though sarcolemma plays a crucial role in cellular Ca2+ transport, little appears to be known about its Ca2+ transporting capability in the diabetic myocardium. In this regard, we have examined the status of the cardiac sarcolemmal Ca2+ pump during diabetes mellitus. Purified sarcolemmal membranes were isolated from male Wistar diabetic rat hearts 8 wk after streptozotocin injection (55 mg/kg iv). Ca2+ pump activity assessed by measuring its Ca2+-stimulated adenosine triphosphatase and Ca2+-uptake ability in the absence and presence of calmodulin was significantly depressed in the diabetic myocardium relative to controls. These results did not appear to have been influenced by the minimal sarcoplasmic reticular and mitochondrial contamination of this membrane preparation. Hence, it appears that the sarcolemmal Ca2+ pump is defective in the diabetic myocardium and may be involved in the altered Ca2+ transport of the heart during diabetes mellitus.
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PMID:Alterations in cardiac sarcolemmal Ca2+ pump activity during diabetes mellitus. 303 Jan 40


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