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)

The functional and structural properties of the monomeric and filamentous actin-myosin head (S1) complexes were compared under strictly controlled conditions which avoid the S1-induced polymerization of monomeric actin. Under these conditions, monomeric (G) and filamentous (F) actin were found to activate S1 Mg(2+)-ATPase by 3- and 120-fold, respectively, in the presence of a 5-fold excess of actin over S1. Using the change in fluorescence intensity of pyrene-G-actin induced by S1 binding in the presence of various nucleotide analogues, we discovered that the ternary G-actin-S1-AMPPNP complex could not be formed. Moreover, the association constants of G-actin to S1-ADP or of ADP to the G-actin-S1 complex were at least an order of magnitude lower than in the filamentous state. Such a low affinity between G-actin and the S1-nucleotide intermediates can reasonably explain the lack of ATPase activation by the monomeric complex. Analysis of the G-actin-S1 interface by chemical cross-linking and limited proteolytic experiments showed that, in the monomeric complex, S1 interacted almost exclusively by its positively charged segment 636-642 with the patch of negative residues located on the actin flexible loops 1-7, 20-28, and 90-100. Moreover, the variation in the cross-linking pattern and in the proteolytic susceptibility of S1 segment 636-642 demonstrated that this electrostatic interface was different in the monomeric and the filamentous complexes. Taken together, the results suggested that the G-actin-S1 interaction encompasses only a small fraction of the strong as well as of the weak F-actin-S1 interface. The monomeric complex would in fact resemble more the collision complex which takes place early in the F-actin-S1 interaction.
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PMID:Comparative studies of the monomeric and filamentous actin-myosin head complexes. 754 71

The functional significance of the interaction of one myosin head (S1) with two actin monomers was investigated by comparing the properties of the cross-linked monomeric and filamentous actin-S1 complexes. S1 was cross-linked to monomeric actin (G-actin) either in the absence or in the presence of DNase I by 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide. The binary G-actin-S1 and ternary DNase I-G-actin-S1 complexes were then purified by a combination of ion exchange and gel filtration columns. Both the binary and the ternary complexes were characterized by negligible, though different, Mg(2+)-ATPase activities of 0.018 and 0.006 s-1s(-1), respectively. Using fluorescence, light-scattering, and ultracentrifugation experiments, we found that only the binary G-actin-S1 complex could be polymerized in the presence of 2 mM MgCl2. Electron microscopic analysis of the cross-linked filamentous complex showed fully decorated filaments with the arrowhead pattern characteristic of the non-covalent complex in the rigor state. Such a 100% cross-linked F-actin-S1 complex exhibited a Mg(2+)-ATPase activity of 6.2 +/- 0.8 s-1, slightly lower than the maximum velocity of the non-cross-linked complex of 8.6 +/- 0.8 s-1, but comparable to the 6.9 +/- 0.6 s-1 obtained for a partially (35%) cross-linked complex. These results implied that the activation of S1 ATPase by actin requires the interaction of S1 with a second actin monomer within the thin filament. They also suggested that the full activation of the filamentous complex is not dependent on the degree of saturation of the thin filament by myosin.
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PMID:Functional significance of the binding of one myosin head to two actin monomers. 754 72

We investigated the mechanism by which caffeine influences myofilament responsiveness to Ca2+ by measuring isometric force, Ca2+ binding, and ATPase activity of dog cardiac myofilament proteins. Caffeine (20 mM) increased submaximal and depressed maximal force in skinned fiber bundles. Although the Ca2+ sensitivity of myofilament activity was increased by caffeine, there was no effect on Ca2+ binding to troponin C (TnC) in skinned fiber bundles. To determine if caffeine altered actin-myosin interaction or affected myosin directly, myofibrillar, actomyosin, and myosin ATPase activities were measured. Maximal Ca(2+)-activated myofibrillar Mg(2+)-ATPase activity was depressed by 20 mM caffeine, whereas submaximal Mg(2+)-ATPase activities were not changed. Actomyosin Mg(2+)-ATPase activity was significantly depressed by caffeine concentrations > or = 15 mM. Myosin Ca(2+)-ATPase activity was depressed by caffeine, whereas Mg(2+)-ATPase and K(EDTA)-ATPase activities were not affected. These data suggest that caffeine affects myofilament function via a mechanism that is independent of TnC-Ca2+ binding but that may involve direct effects on actin-cross-bridge interaction.
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PMID:Caffeine alters cardiac myofilament activity and regulation independently of Ca2+ binding to troponin C. 761 52

Lipid composition, fluidity, and Na+,K(+)-adenosine triphosphatase (ATPase), Mg(2+)-ATPase, and acetylcholinesterase (AChE) activities of erythrocyte membranes were examined in comparison to plasma lipid composition and lecithin:cholesterol acyltransferase (LCAT) activities in 39 patients with hepatic cirrhosis due to viral hepatitis (Child-Pugh class A, n = 12; class B, n = 13; and class C, n = 14). Plasma LCAT activities decreased and the plasma free-cholesterol to phospholipid molar ratio (C/PL) increased with progressive severity of hepatic cirrhosis. C/PL and fluorescence polarization (inverse of fluidity) of erythrocyte membranes also increased with disease progression (C/PL: Child-Pugh A, 0.911 +/- 0.010; B, 0.941 +/- 0.011; C, 0.979 +/- 0.028; and normal, 0.798 +/- 0.010; fluorescence polarization: Child-Pugh A, 0.348 +/- 0.002; B, 0.351 +/- 0.002; C, 0.355 +/- 0.002; and normal, 0.340 +/- 0.002). There was a correlation between C/PL and fluorescence polarization of erythrocyte membranes (r = .629, P < .001). Na+,K(+)-ATPase activity of erythrocyte membranes did not differ between cirrhotic patients and normal subjects. On the other hand, Mg(2+)-ATPase activity decreased in Child-Pugh C cirrhosis. AChE activity was decreased in Child-Pugh A cirrhosis, and decreased further in Child-Pugh B and C cirrhosis. AChE and Mg(2+)-ATPase activities correlated inversely with fluorescence polarization (r = -.652, P < .001 and r = -.381, P < .01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Altered lipid composition and differential changes in activities of membrane-bound enzymes of erythrocytes in hepatic cirrhosis. 761 39

The activity of Mg(2+)-ATPase was studied in the tissues, homogenates, specimens of rat spermatic and adrenal glands during postmortem autolysis. The initial enzymatic activity was 2-fold higher in adrenal tissue, homogenate and mitochondria than in spermatic ones. As autolysis proceeded in the tissue and homogenate of the adrenal and spermatic glands, and spermatic mitochondria, the ATPase activity was drastically decreased, by disappearing completely at hour 24 of autolysis. At the same time, the enzyme from adrenal mitochondria exhibited a higher stability. Of great importance for this can be rearrangements in the phospholipid profile of the corresponding membranous structures, as well as hormonal factors.
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PMID:[Changes in ATPase activity in tissues and mitochondria of some steroid-producing rat organs during autolysis]. 761 98

We describe, for the first time, the reaction of skeletal myosin subfragment 1 (S-1) with the succinimido ester of 6-[fluorescein-5(and 6)-carboxamido]hexanoic acid (FHS), which takes place at pH 7.0, 20 degrees C, within a 15 min period, in the presence of 1.5-1.8-fold molar excess of reagent over protein. As a result, 0.9-1.0 mol of fluorescyl group/mol of S-1 was covalently incorporated exclusively into the 95 kDa heavy chain as monitored by spectroscopic measurements. The central 50 kDa segment included the main site of fluorescence attachment as assessed by gel electrophoresis. The extent of S-1--FHS conjugation is strongly sensitive to F-actin binding but not to the interaction of nucleotides. The formation of the rigor F-actin--S-1 complex decreased the level of S-1 labeling to 20% without any competition between actin and S-1 for FHS binding. The derivatization of S-1 did not alter the K(+)-ATPase activity, but it enhanced the Ca(2+)-ATPase and Mg(2+)-ATPase to 150% and 225%, respectively, whereas it lowered the actin-activated ATPase to only 75% of the original activity. A double-reciprocal plot of the ATPase rate against actin concentration indicated a 2-fold decrease of the Vmax value for modified S-1, while the Km for actin was unchanged. Cosedimentation experiments did not reveal disruption of the rigor acto-S-1 interaction by the bound fluorophore. The labeled S-1 heavy chain was isolated, and its total tryptic digest was fractionated by reverse-phase HPLC.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Production and properties of skeletal myosin subfragment 1 selectively labeled with fluorescein at lysine-553 proximal to the strong actin-binding site. 762 19

The purpose of this study was to determine whether myocardial adenosine triphosphatase (ATPase) activities were reduced in pigs with naturally occurring hypertrophic cardiomyopathy (HCM). The selection of hearts for the HCM and the normal control groups depended on histological examination. Specific ATPase activity and 5'-nucleotidase activity were measured in left ventricular myocardium obtained from HCM (n = 7) and normal control (n = 7) animals. The histological features of HCM included marked disorientation of muscle cells, thickening of the intramural coronary arterial wall with a narrowed lumen, endocardial fibrosis and myocardial fibrosis. The HCM group showed significant increases in both heart weight (32%) and heart weight to body weight ratio (46%). The total ATPase activity in crude homogenates from the HCM group was significantly decreased by 16%. Azide-sensitive ATPase (mitochondrial ATPase) activity, ouabain-sensitive ATPase (Na+, K+-ATPase) activity, basal Mg(2+)-ATPase activity and Ca(2+)-ATPase activity were all significantly decreased by 18%, 30%, 20% and 50%, respectively. In contrast, no significant decrease was found in the mean values for 5'-nucleotidase activity. These results suggest that myocardial ATPase activities are suppressed in pigs with naturally occurring HCM.
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PMID:Altered adenosine triphosphatase activities in pigs with naturally occurring hypertrophic cardiomyopathy. 764 94

The effect of DL alpha-lipoic acid on the nephrotoxic potential of gentamicin was examined. Intraperitoneal injection of gentamicin (100 mg/kg/day) to rats resulted in decreased activity of the glycolytic enzymes-hexokinase, phosphoglucoisomerase, aldolase and lactate dehydrogenase. The two gluconeogenic enzymes--glucose-6-phosphatase and fructose-1,6-diphosphatase, the transmembrane enzymes namely the Na+, K(+)-ATPase, Ca(2+)-ATPase, Mg(2+)-ATPase and the brushborder enzyme alkaline phosphatase, also showed decreased activities. This decrease in the activities of ATPases and alkaline phosphatase suggests basolateral and brush border membrane damage. Decreased activity of the TCA cycle enzymes isocitrate dehydrogenase (ICDH), succinate dehydrogenase (SDH) and malate dehydrogenase (MDH), suggests a loss in mitochondrial integrity. These biochemical disturbances were effectively counteracted by lipoic acid administration. Lipoic acid administration by gastric intubation at two different concentrations (10 mg and 25 mg/kg/day) brought about an increase in the activity of the glycolytic enzymes, ATPases and the TCA cycle enzymes. The gluconeogenic enzymes however showed a further decrease in their activities at both the concentrations of lipoic acid administered. These observations shed light on the nephroprotective action of lipoic acid against experimental aminoglycoside toxicity and the protection afforded at 25 mg/kg/day of lipoic acid was noted to be higher than that at 10 mg level.
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PMID:Role of DL alpha-lipoic acid in gentamicin induced nephrotoxicity. 765 73

1. The present study deals with astrocyte cultures as a model for studying the membrane-mediated central nervous system-depressing effect of organic solvents. 2. The primary astrocyte cultures were prepared from neonatal rat cerebella. The cells were cultured in modified essential medium. The astrocyte membranes isolated from the cultures were exposed to solvents in incubation mixture at different dose levels (3, 6 and 9 mmol/L) for 1 h. The physiologically important integral proteins Na+, K(+)-ATPase and Mg(2+)-ATPase were studied. 3. The aromatic hydrocarbons (benzene, toluene, styrene, xylene and ethylbenzene) inhibited the ATPase activities according to their lipid solubilities. n-Hexane and cyclohexane clearly had less effect than aromatic hydrocarbons, despite their greater lipid solubilities. 4. Astrocytes were shown to be sensitive targets to the effects of organic solvents, measured as the inhibition of the integral enzymes Na+, K(+)-ATPase and Mg(2+)-ATPase.
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PMID:Effects of selected organic solvents on the astrocyte membrane ATPase in vitro. 767 44

Quercetin (Que) ig 200 mg.kg-1, qd x 14 d decreased activities of the Na(+)-K(+)-exchanging ATPase (I) of rat brain plasma membranes and heart sarcolemmal and Ca(2+) Mg(2+)-ATPase (II) of heart sarcolemmal membrane. Que 100 mg.kg-1 reduced the activity of I from rat heart sarcolemmal preparation, but had no effect on that from rat brain plasma membranes. The result shows that I of myocardium is more sensitive than that of brain in rat. Que also showed a remarkable inhibitory effect in the II of heart sarcolemma.
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PMID:Effects of quercetin on Na(+)-K(+)-exchanging ATPase and Ca(2+) Mg(2+)-ATPase in rats. 771 64


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