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)

Membrane fractions enriched in sarcoplasmic reticulum (SR) were isolated from the cardiac ventricles of 10-month-old, stroke-prone spontaneously hypertensive rats (SHRSP) which had been maintained for nine months on one of four experimental diets: low protein (LP) (19% protein), standard (STD) (24% protein), high protein (HP) (32% protein), or high methionine (1.9% methionine) (MET). ATPase activities, as well as ATP-dependent Ca2+ binding and Ca2+-uptake activities, of the isolated SR were determined to examine the influence of diet on myocardial Ca2+-pump activity. SR from all four groups exhibited similar Mg2+-ATPase activity. However, the (Ca2+ + Mg2+)-ATPase activity was significantly elevated in SR from rats on the MET diet while the activity in the other groups showed no significant differences. After 15 sec of incubation, Ca2+-uptake (presence of oxalate) in SR from the LP group was significantly less than Ca2+-uptake in SR from each of the three other diet groups. Ca2+ binding (absence of oxalate) in the SR from the LP group was also significantly less than that from each of the three other diet groups. Kinetic analysis of SR Ca2+-uptake over 60 sec revealed that the Bmax of the MET group was significantly higher than Bmax of the STD diet group. In addition, the Bmax of the LP group was significantly lower than Bmax of the HP and MET groups. There was no significant difference in affinity of the SR Ca2+-uptake system among the four diet groups. These results indicate that modification of dietary protein can influence myocardial SR Ca2+-pump function.
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PMID:ATP-dependent calcium uptake in myocardial sarcoplasmic reticulum from spontaneously hypertensive rats: effect of modification of dietary protein. 293 82

Membrane vesicles capable of energized Ca2+ pumping have been reconstituted from cardiac sarcoplasmic reticulum (SR). Cardiac SR was solubilized with Triton X-100 in a detergent to protein weight ratio of 0.8, and membranous vesicles were reconstituted by removal of detergent with Bio-Beads SM-2 (a neutral porous styrene-divinylbenzene copolymer). The reconstituted vesicles exhibited ATP-dependent oxalate-facilitated Ca2+ accumulation with rates and efficiency comparable to the best reconstituted skeletal muscle preparation (Ca2+-loading rate = 1.65 +/- 0.31 mumol mg-1 min-1, Ca2+-activated ATPase activity = 2.39 +/- 0.25 mumol mg-1 min-1, efficiency (Ca2+/ATP) = 0.69 +/- 0.09). Phospholamban in the reconstituted vesicles was phosphorylated with added catalytic subunit of cAMP-dependent protein kinase to almost the same extent as that in original vesicles. However, phosphorylation of phospholamban had no effect on the Ca2+ accumulation of the reconstituted vesicles. This is to be contrasted with a decrease in the half-maximal concentration of Ca2+ for Ca2+ accumulation (KCa) in the original vesicles from 1.35 +/- 0.08 microM to 0.75 +/- 0.12 microM by cAMP-dependent phosphorylation of phospholamban. On the other hand KCa for the reconstituted vesicles was about 0.5 microM and remained unchanged by phosphorylation, indicating that the Ca2+ pump in the reconstituted vesicles is already fully activated. These results suggest that in normal cardiac SR, phospholamban in the dephosphorylated state acts as a suppressor of the Ca2+ pump and that phosphorylation of phospholamban serves to reverse the suppression.
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PMID:The nature of the modulation of Ca2+ transport as studied by reconstitution of cardiac sarcoplasmic reticulum. 293 32

Normothermic global ischemia of 7, 10, 15 and 60 min was found to depress oxalate supported calcium uptake rate measured either in unfractionated homogenates or isolated sarcoplasmic reticulum. The degree of depression increased with the duration of ischemia. Comparison of the isolated sarcoplasmic reticulum with unfractionated homogenates showed that the isolated sarcoplasmic reticulum was more damaged by ischemia than the unfractionated homogenate. The cause of this discrepancy was not due to inactivation of sarcoplasmic reticulum during isolation but was due to the discard of greater portions of undamaged sarcoplasmic reticulum as the ischemic period increased. Ischemia preferentially affected that sarcoplasmic reticulum most easily fragmented by homogenization. To determine if the depression of sarcoplasmic reticulum function is uniform throughout the isolated fraction, we compared several properties of the isolated fractions. After 10 min of ischemia, extensive properties such as calcium oxalate uptake rate, calcium ATPase rate, calcium oxalate capacity and steady-state calcium loading were depressed 50, 41, 48 and 24% respectively. In contrast, intensive properties such as permeability, calcium-ATPase turnover rate, and ratio of forward nucleotide flux to reverse nucleotide flux were unaffected by ischemia. However, one intensive property, the coupling ratio, was depressed 20%. We conclude from this difference in the effects of ischemia on extensive and intensive properties that the major effect of ischemia is to inactivate the Ca-ATPase.
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PMID:Effects of ischemia on the isolation and function of canine cardiac sarcoplasmic reticulum. 294 2

Microsomal fractions prepared from porcine thyroid glands by differential centrifugations and sucrose density gradient centrifugation showed an ATP-dependent Ca2+ uptake. Electron microscopy and the study of marker enzyme activities suggested that the fractions consisted mainly of endoplasmic reticulum. The amount of transported Ca2+ increased four times in the presence of 20 mM oxalate owing to the precipitation of calcium oxalate, which was detected inside the microsomal vesicles by electron microscopy. Ca2+ was released rapidly when the calcium ionophore, A-23187, was added. The Ca2+ concentration for the half-maximal activation of Ca2+ transport was about 1 microM. These results indicate that Ca2+ is translocated into the lumen of microsomes against a concentration gradient in a manner of the active transport. The microsomes showed Ca2+-dependent ATPase activity and were phosphorylated by the reaction with [gamma-32P]ATP in a similar Ca2+ dependence to that of transport rate. A 105-kDa phosphoprotein was identified by dodecyl sulfate polyacrylamide gel electrophoresis and was found to be sensitive to hydroxylamine. These properties of the phosphoprotein were the same as those of Ca2+ pump ATPase in the endoplasmic reticulum of other cells. These results suggest that the cytosolic Ca2+ is maintained at low levels by the microsomal uptake of Ca2+ by the action of the ATP-dependent Ca2+ pump or active transport system.
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PMID:Active calcium transport by porcine thyroid microsomes. 294 12

A monoclonal antibody (2B3) directed against the calmodulin-binding (Ca2+ + Mg2+)-dependent ATPase from pig stomach smooth muscle was prepared. This antibody reacts with a 130,000-Mr protein that co-migrates on SDS/polyacrylamide-gel electrophoresis with the calmodulin-binding (Ca2+ + Mg2+)-ATPase purified from smooth muscle by calmodulin affinity chromatography. The antibody causes partial inhibition of the (Ca2+ + Mg2+)-ATPase activity in plasma membranes from pig stomach smooth muscle, in pig erythrocytes and human erythrocytes. It appears to be directed against a specific functionally important site of the plasmalemmal Ca2+-transport ATPase and acts as a competitive inhibitor of ATP binding. Binding of the antibody does not change the Km of the ATPase for Ca2+ and its inhibitory effect is not altered by the presence of calmodulin. No inhibition of (Ca2+ + Mg2+)-ATPase activity or of the oxalate-stimulated Ca2+ uptake was observed in a pig smooth-muscle vesicle preparation enriched in endoplasmic reticulum. These results confirm the existence in smooth muscle of two different types of Ca2+-transport ATPase: a calmodulin-binding (Ca2+ + Mg2+)-ATPase located in the plasma membrane and a second one confined to the endoplasmic reticulum.
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PMID:A monoclonal antibody to the calmodulin-binding (Ca2+ + Mg2+)-dependent ATPase from pig stomach smooth muscle inhibits plasmalemmal (Ca2+ + Mg2+)-dependent ATPase activity. 295 Aug 52

We have characterized ATP-dependent Ca2+ transport into highly purified plasma membrane fraction isolated from guinea pig ileum smooth muscle. The membrane fraction contained inside-out sealed vesicles and was enriched 30-40-fold in 5'-nucleotidase and phosphodiesterase I activity as compared to post nuclear supernatant. Plasma membrane vesicles showed high rate (76 nmol/mg/min) and high capacity for ATP dependent Ca2+ transport which was inhibited by addition of Ca2+ ionophore A23187. The inhibitors of mitochondrial Ca2+ transport, i.e., sodium azide, oligomycin and ruthenium red did not inhibit ATP-dependent Ca2+ uptake into plasma membrane vesicles. The energy dependent Ca2+ uptake into plasma membranes showed very high specificity for ATP as energy source and other nucleotide triphosphates were ineffective in supporting Ca2+ transport. Phosphate was significantly better as Ca2+ trapping anion to potentiate ATP-dependent Ca2+ uptake into plasma membrane fraction as compared to oxalate. Orthovanadate, an inhibitor of cell membrane (Ca2+-Mg2+)-ATPase activity, completely inhibited ATP-dependent Ca2+ transport and the Ki was approximately 0.6 microM. ATP-dependent Ca2+ transport and formation of alkali labile phosphorylated intermediate of (Ca2+-Mg2+)-ATPase increased with increasing concentrations of free Ca2+ in the incubation mixture and the Km value for Ca2+ was approximately 0.6-0.7 microM for both the reactions.
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PMID:Characterization of Ca2+ uptake in plasma membrane vesicles isolated from guinea pig ileum smooth muscle. 295 Oct 13

Human liver microsomal fractions exhibit ATP-supported Ca2+ uptake which is half-maximal at 7 X 10(-7) M free Ca2+ in the presence of oxalate. Ca2+ uptake is coupled to a Ca2+-stimulated ATPase activity, which is half-maximal at 4 X 10(-7) M free Ca2+. Catalysis involves formation of an Mr = 116,000 phosphoprotein with stability characteristics of an acylphosphate compound suggested to represent a phosphoryl protein intermediate of the Ca2+-ATPase. Phosphorylation is half-maximal at about 10(-6) M free Ca2+. The Mr = 116,000 protein is highly susceptible to proteolysis with trypsin. The phosphorylated active site was localized in an Mr = 58,000 primary tryptic fragment and in an Mr = 34,000 subfragment. Analyses on the mechanism of the Ca2+-ATPase suggest the following reaction sequence: formation of an ADP-reactive phosphoenzyme (Mr = 116,000) with bound Ca2+, which can transphosphorylate its Pi to ADP, giving rise to synthesis of ATP; reversible transformation of the ADP-reactive phosphoenzyme into an isomer without bound Ca2+, which cannot further react with ADP; hydrolytical cleavage, probably catalyzed by Mg2+, of the ADP-unreactive phosphoenzyme with liberation of Pi. Comparison with the Ca2+-transport ATPase in sarcoplasmic reticulum of skeletal muscle led us to suggest that the Mr = 116,000 Ca2+-ATPase belongs to the class of E1P . E2P-ATPases and might be operative as a Ca2+-transport ATPase at the level of the endoplasmic reticulum in human liver.
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PMID:Ca2+-activated ATPase in microsomes from human liver. 295 25

Platelet plasma and intracellular membrane fractions were isolated from a mixed membrane fraction after sucrose cushion centrifugation. Their previous identification through biochemical and immunological characterization is now confirmed by sodium dodecyl sulfate electrophoresis of the membrane proteins which reveals a different protein profile. The two associated calcium transport systems showed a different time course and exhibited different oxalate sensitivity. The plasma membranes are not permeable to potassium oxalate but the Ca2+ uptake was stimulated by potassium oxalate in intracellular membranes. We then focused on the study of the plasma membrane-associated Ca2+-activated ATPase which shows the following characteristics: a linearity in the time course until 30 min, an apparent affinity toward calcium of about 10(-7) M without detectable inhibition at higher concentrations, a maximal activity at pH 8, a high ATP requirement because the maximal response was obtained with 200 microM, and a high specificity toward ATP as energy donor. Taken together, these studies indicate the possible involvement of both a plasma membrane and a dense tubular system Ca2+-ATPase in the regulation of Ca2+ concentration in human platelets.
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PMID:Two different Ca2+ transport systems are associated with plasma and intracellular human platelet membranes. 295 59

Isolated cardiac Ca,Mg-dependent ATPase of the sarcoplasmic reticulum and purified phospholamban, a proteolipid involved in the regulation of the calcium transport systems of the heart muscle, were reconstituted into soybean lecithin liposomes. Whereas the enzymatic activity of the CaATPase in the obtained liposomes was unaffected as well as by unphosphorylated and cAMP-dependent phosphorylated phospholamban, the capacity of oxalate-supported calcium uptake was lowered in the presence of phospholamban. The proteolipid is discussed not as a regulatory protein of the enzyme but as a mediator of the calcium storage in the lumen of the liposomes or sarcoplasmic reticulum network.
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PMID:Reconstitution of phospholamban--an approach to its function. 296 26

Phospholamban, a phosphorylatable protein of the cardiac sarcoplasmic reticulum, has been estimated by a semi-quantitative immunoassay. It can be determined in purified membrane preparations as well as in crude fractions of cardiac muscle membranes, regardless of the phosphorylation state of the phosphoprotein. The content of phospholamban in mammalian heart muscle membrane vesicles correlates with the activity of the calcium/magnesium-dependent ATPase with the exception of the oxalate-loaded membrane preparations. This observation indicates that phospholamban and the calcium transporting enzyme are localized at different sites in cardiac sarcoplasmic reticulum.
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PMID:An enzyme immunoassay for phospholamban. 296 99


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