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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)

Erythrocyte membranes prepared by three different procedures showed (Mg2+ + Ca2+)-ATPase activities differing in specific activity and in affinity for Ca2+. The (Mg2+ + Ca2+)-ATPase activity of the three preparations was stimulated to different extents by a Ca2+-dependent protein activator isolated from hemolysates. The Ca2+ affinity of the two most active preparations was decreased as the ATP concentration in the assay medium was increased. Lowering the ATP concentration from 2 mM to 2-200 microM or lowering the Mg:ATP ratio to less than one shifted the (Mg2+ + Ca2+)-ATPase activity in stepwise hemolysis membranes from mixed "high" and "low" affinity to a single high Ca2+ affinity. Membranes from which soluble proteins were extracted by EDTA (0.1 mM) in low ionic strength, or membranes prepared by the EDTA (1-10 mM) procedure, did not undergo the shift in the Ca2+ affinity with changes in ATP and MgCl2 concentrations. The EDTA-wash membranes were only weakly activated by the protein activator. It is suggested that the differences in properties of the (Mg2+ + Ca2+)-ATPase prepared by these three procedures reflect differences determined in part by the degree of association of the membrane with a soluble protein activator and changes in the state of the enzyme to a less activatable form.
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PMID:Properties of (Mg2 + Ca2+)-ATPase of erythrocyte membranes prepared by different procedures: influence of Mg2+, Ca2+, ATP, and protein activator. 15 19

Inhibition of the myosin ATPase by vanadate ion (Vi) has been studied in 90 mM NaCl/5 mM MgCl2/20 mM Tris-HCl, pH 8.5, at 25 degrees C. Although the onset of inhibition during the assay is slow and dependent upon Vi concentration (kapp approximately 0.3 M-1 s-1), the final level of inhibition approaches 100%, provided the Vi concentration is in slight excess over the concentration of ATPase sites. Inhibition is not reversible by dialysis or the addition of reducing agents. The source of this irreversible inhibition consists of the formation of a stable, inactive complex with the composition M . ADP . Vi (where M represents a single myosin active site). The complex has been isolated, and its mechanism of formation from M, ADP, and Vi has been studied. Omission of ATP increases the rate of formation by about 35-fold (kapp approximately 11 M-1 s-1), yet this rate is still low in comparison with the rates of simple protein-ligand association reactions. This slowness is interpreted in terms of a rate-limited isomerization step that follows the association of M+, ADP, and Vi: M+ . ADP . Vi leads to M+. ADP . Vi (+ indicates the inactive product of the isomerization). The properties of M.ADP.Vi are compared with those of the ATPase intermediate M**.ADP . Pi, and the possible role of Vi as an analog of Pi is discussed.
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PMID:Inhibition of myosin ATPase by vanadate ion. 15 22

The activation of the coupling factor-latent ATPase enzyme by tryptic proteolysis may resemble the activation of many proenzymes by limited proteolysis. The beta (53 000 dalton) subunit of solubilized coupling factor-latent ATPase from Mycobacterium phlei was selectively lost in some trypsin-treated samples. Since a concomitant loss of ATPase activity was not observed, the beta subunit may not be essential for ATPase catalytic activity. Treatment of solubilized coupling factor with chymotrypsin rapidly produced an A'-type (61 000 dalton) species from the native alpha (64 000 dalton) subunits with partial activation of the APTase enzyme. Secondary chymotryptic cleavage yielded an A"-type (58 000 dalton) species and a less-active enzyme. Storage of fresh coupling factor samples at -20degreeC in the presence of 4 mM MgCl2 with several freeze-thaw cycles resulted in loss of ATPase activity without apparent change in alpha subunit structure. Storage at 4 degrees C in the presence or absence of MgCl2 both decreased ATPase activity and generated A'-type alpha subunit species. Since presence was suspected. The peptide bonds first cleaved by trypsin, chymotrypsin, and the unknown protease are all apparantly located within the same small segment of alpha subunit polypeptide chain.
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PMID:Limited proteolysis of coupling factor-latent ATPase from Mycobacterium phlei. Effects of different enzymes and modifying agents. 15 59

A factor termed Physarum actinin was isolated and partially purified from plasmodia of a myxomycete, Physarum polycephalum. When Physarum actinin was mixed with purified Physarum or rabbit striated muscle G-actin in a weight ratio of about 1 actinin to 9 actin and then the polymerization of G-actin induced, G-actin polymerized to the ordinary F-actin on addition of 0.1 M KCl. However, it polymerized to Mg-polymer on addition of 2 mM MgCl2. The reduced viscosity (etasp/C) of the Mg-polymer was 1.2 dl/g, about one-seventh of that of the F-actin (7.4 dl/g). The sedimentation coefficient of the Mg-polymer was 22.8 S, almost the same as that of the F-actin (29.4 S). The Mg-polymer showed the specific ATPase activity of the order of 1 . 10(-3) mumol ATP/mg actin per min. It was shown that Physarum actinin copolymerized with G-actin to form Mg-polymer on addition of 2 mM MgCl2. The molecular weights of Physarum actinin were about 90 000 in salt-free or slat solutions and 43 000 in a dodecyl sulfate solution. The range of salting out with ammonium sulfate was 50--65% saturation, which was different from that of Physarum actin (15--35% saturation). Physarum actinin did not interact with Physarum myosin or muscle heavy meromyosin. When the weight ratio of actinin to actin increased, the flow birefringence of the formed Mg-polymer decreased, and it became almost zero at the weight ratio of 1 actinin to 5 actin. ATPase activity reached the maximum level (2.2 . 10(-3) mumol ATP/mg actin per min) at the same ratio. On the addition of Physarum actinin to purified Physarum F-actin which had been polymerized on addition of 2 mM MgCl2 the viscosity decreased rapidly, suggesting that the F-actin filaments were broken in the smaller fragments or that they transformed to Mg-polymers. A factor with properties similar to Physarum actinin was isolated from acetone powder of sea urchin eggs.
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PMID:Some properties of Physarum actinin. A regulatory protein of actin polymerization. 15 67

Fluorescent cyanine (diS-C3-(5), diS-C2-(5), diO-C3-(5)) and oxonol (diBA-C4-(5)) potential-dependent dyes appeared to be extremely effective in detecting and studying the potential formed on the fragmented sarcoplasmic reticulum membrane under Ca2+ transport When [Ca2+] less than 5 X 10(-7) M ATP hydrolysis leads to formation of transmembrane potential (positive inside vesicules) caused by the Ca-independent ATPase activity. The potential is formed by a monovalent ion, presumably by H+, and possibly by Mg2+ ions. Ca-dependent ATPase activation by Ca2+ makes the potential to drop sharply and successive Ca2+ transport proceeds at low potential value. When Ca2+ has been accumulated by vesicules the Ca-independent ATPase restores positive potential. The potentials generated by both Ca-independent (10--30 mv) and Ca-dependent (-20 divided by -40 mv) ATPases have been estimated on the basis of the Nernst's equation with the help of positive and negative diffusion potentials formed by MgCl2 and CaCl2 gradients. The Ca2+ transport is shown not to be due to transmembrane electrophoresis but Ca-dependent ATPase action. The results suggest quite clearly that Ca-dependent ATPase operates as electrogenic Ca2+/H+, Mg2+-exchanger. The functional role of Ca-independent ATPase is, possibly, in compensation of charge effects when Ca2+ ions are passing through the membranes. The model illustrating the electrogenicity of Ca-independent and Ca-dependent ATPases action during Ca2+ transport in SR membranes has been proposed.
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PMID:[Transmembrane potential formation upon ATP hydrolysis in sarcoplasmic reticulum]. 15 68

Partial reactions of potassium-stimulated ATP phosphohydrolase from hog gastric mucosa were studied by means of a rapid-mixing apparatus. At 21 degrees C, in the presence of 2 mM MgCl2 and 5 microM [gamma-32P]ATP there was a rapid phosphorylation of the enzyme with a pseudofirst order rate constant of 1400 min-1. Addition of the ATP about 120 ms before the MgCl2 increased this rate constant to 4400 min-1. In the absence of MgCl2 there was no phosphorylation. Addition of 4 or 10 mM KCl to the phosphoenzyme which had been formed in the absence of KCl produced a rapid initial rate of dephosphorylation (k = 2600 and 3200 min-1 respectively). An additional slow component of dephosphorylation was observed when unlabeled ATP was added together with the KCl (k = 700 to 900 min-1). At a 4 mM concentration, KCl stimulated the ATPase activity about 9-fold. At higher concentrations, the activity was reduced in parallel with a reduction of the steady state level of phosphoenzyme. Addition of KCl to the enzyme before the addition of ATP plus MgCl2 resulted in a low rate and extent of phosphorylation. KCl appeared to inhibit the phosphorylation at a level preceeding the E.ATP complex.
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PMID:Phosphorylation and dephosphorylation kinetics of potassium-stimulated ATP phosphohydrolase from hog gastric mucosa. 15 3

1. Grinding of epimastigotes of Trypanosoma cruzi with glass powder in a mortar yielded a Mg2+-activated adenosine triphosphatase (ATPase) preparation which was highly sensitive to oligomycin. 2. Chloroform treatment of the particles resulted in the solubilization of an ATPase which was (a) activated by MgCl2; (b) slightly inhibited by CaCl2; (c) activated by sulphite and bisulphite; (d) had an optimum pH of 7.6; and (e) had a Km for ATP of 2.1 mM (in the presence of 4 mM MgCl2). 3. The solubilized enzyme was insensitive to oligomycin and leucinostatin, which inhibited the membrane-bound ATPase, though inhibited by efrapeptin and quercetin. 4. The results indicate that the chloroform-extracted enzyme is a soluble F1-ATPase similar to those isolated from mammalian mitochondria.
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PMID:Solubilization and some properties of the Mg2+-activated adenosine triphosphatase from Trypanosoma cruzi. 16 84

The content of coenzyme A-SH (CoASH) and acetyl-CoA of suspensions of rat heart mitochondria was stabilized by the addition of DL-carnitine and acetyl-DL-carnitine, in the presence of the respiratory inhibitor rotenone. The mitochondrial content of NAD+ and NADH was similarly stabilized by the addition of acetoacetate and DL-3-hydroxybutyrate, and the content of ADP and ATP was imposed by the addition of these nucleotides to the mitochondrial suspension, in the presence of uncoupling agent and oligomycin, to inhibit ATPase. Under these conditions, mitochondrial CoASH/acetyl-CoA, NAD+/ NADH, and ADP/ATP ratios could be varied independently, and the effect on the interconversion of active and inactive pyruvate dehydrogenase could be studied. Decreases in both CoASH/acetyl-CoA and NAD+/NADH ratios were shown to be inhibitory to the steady state activity of pyruvate dehydrogenase, and this effect is described at three different ADP/ATP ratios and different concentrations of added MgCl2. A new steady state level of activity was achieved within 10 min of a change in either CoASH/acetyl-CoA or NAD+/NADH ratio; the rate of inactivation was much higher than the rate of reactivation under these conditions. Effects of CoASH/acetyl-CoA and NAD+/NADH may be additive but are still quantitatively lesser than the changes in activity of pyruvate dehydrogenase induced by changes in ADP/ATP ratio. The variation in activity of pyruvate dehydrogenase with ADP/ATP ratio is described in the absence of changes in the other two ratios, conditions which were not met in earlier studies which employed the oxidation of different substrates to generate changes in all three ratios.
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PMID:Studies on the effects of coenzyme A-SH: acetyl coenzyme A, nicotinamide adenine dinucleotide: reduced nicotinamide adenine dinucleotide, and adenosine diphosphate: adenosine triphosphate ratios on the interconversion of active and inactive pyruvate dehydrogenase in isolated rat heart mitochondria. 18 82

1. Starting from the spectrophotometric method of Ballard optimal reaction conditions for measurements of galactokinase in piglet liver were systematically studied. These are (final conc. in the test): 100 mM triethanolamine-HCl buffer, 33 mM KCl, 16.5 mM NaF (inhibiting ATPase), 5 mM cysteine hydrochloride, 0.33 mM NADH2, 1 U pyruvate kinase and lactic dehydrogenase, 0.5 mM phosphoenolpyruvate, 1.5 mM galactose, 0.5 mM ATP and 1 mM MgCl2, final pH 7.5. 2. An optimal substrate concentration, a Mg: ATP-ratio of 2:1, pH-stability and addition of activators are important for the determination of galactokinase activity in the supernatant fraction of pig liver. 3. Using the optimized method galactokinase activity of pig liver in dependence on age, with particular reference to the perinatal period, was determined. 4. Galactokinase activity of liver of newborn piglets is 7 times that of adult pigs. In the suckling period the activity remains relatively constant at this high level and decreases remarkably immediately after weaning. 5. Galactokinase of liver of newborn piglets differs in kinetic properties (lower Km of ATP, higher maximal reaction velocity) from the enzyme of adult pigs, which is still insufficient to make sure the existence of two different forms of the enzyme.
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PMID:[Determination, proprerties and postnatal development of galactokinase in the swine liver]. 20 76

Pb2+-stimulated phosphorylation of Electrophorus electricus electroplax (Na+ + K+)-adenosine triphosphatase is prevented by stoichiometric quantities of 2,3-dimercaptopropanol. The chelator in the same low concentrations does not block Na+-dependent phosphorylation. Both Pb2+-and Na+-dependent phosphorylation reactions show the same dependence on MgCl2. Phosphorylation in the presence of both Na+ and Pb2+ is cumulative suggesting that Pb2+ and Na+ bind at separate, independent sites. The enthalpy change due to binding of Pb2+ is about -1.76 kcal/mol. 32P-phosphopeptides obtained from pronase or pepsin digests of Pb2+-and Na+-dependent phosphoproteins are electrophoretically identical. Pb2+ does not stimulate but does inhibit ATP-ADP exchange activity under the conditions in which this activity is stimulated by Na+. Since the phosphorylation sites are identical, it is concluded that the differences in reactivity of the Na+- and Pb2+-phosphoenzymes are due to different conformational changes produced by binding of Na+ and Pb2+. The Pb2+-sensitive conformation is critical for Na+ specificity of phosphorylation, reversibility of phosphorylation, and for phosphatase activity but not for acceptor site phosphorylation by ATP. These findings have implications for enzyme reaction models.
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PMID:Characteristics of lead ion-stimulated phosphorylation of Electrophorus electricus electroplax (Na+ + K+)-adenosine triphosphatase and inhibition of ATP-ADP exchange. 21 19


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