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Query: EC:3.6.3.1 (Mg2+-ATPase)
 1,484 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The structure of a tryptic peptide containing one specific sulfhydryl group (Sa), which is responsible for the activation of Mg2+-ATPase of myosin B and is present in the light meromyosin region of the myosin molecule, was studied. The amino acid sequence was deduced to be Thr (or Ser)-Asn-Ala-Ala-Cys-Ala-Ala-Leu-Asp-Lys-Lys. In addition, a space-filling model around Sa was built up by comparing Sa-peptide with the amino acid sequence around Cys 190 of alpha-tropomyosin, and the high reactivity of Sa with N-ethylmaleimide is considered based on this model.
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PMID:The sulfhydryl groups involved in the active site of myosin B adenosinetriphosphatase. IV. Structure around the Sa thiol group. 14 8

The synthesis, proof of structure, and biological activity of some new steroidal 17beta-formyl guanylhydrazones are described. The guanylhydrazones of nondigitalis-like steroids inhibited myocardial Na+,K+-ATPase but had only a depressant effect on myocardial contractility. By comparison, the corresponding guanylhydrazone of a digitalis-like steroid gave a positive inotropic effect in concentrations that also inhibited Na+,K+-ATPase. The nondigitalis-like guanylhydrazones also inhibited membrane Mg2+-ATPase and this may infer that the compounds act nonspecifically by membrane stabilization rather than by interaction with stereoselective receptors. Biological activity was determined in the guinea pig.
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PMID:Cardenolide analogues. 7. Synthesis and biological activity of some new steroidal guanylhydrazones. 14 38

1. Tropomyosin, one of the regulatory proteins in muscle contraction, was prepared from chickens, rabbits, frogs, shrimps, and shellfish, and conserved characteristics were studied using an enzymological technique. 2. All tropomyosins tested, irrespective of their sources, were found to have the ability to mediate the inhibitory activity of rabbit troponin toward rabbit Mg2+-activated actomyosin ATPase (Mg2+-ATPase) activity in the absence of Ca2+ ions. 3. The effect of tropomyosin on the Mg2+-ATPase activity in the presence of Ca2+ ions varied, depending on the source, and this variation appeared to reflect the evolutionary course of this protein. 4. Tropomyosin from shellfish adductor muscle had the ability to bind to rabbit skeletal muscle troponin and actin. This ability is also considered to be a basic characteristic of tropomyosin which has been conserved during evolution.
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PMID:The functional characteristics conserved in tropomyosins. 14 70

Effects of commonly used purification procedures on the yield and specific activity of (Na+ + K+)-ATPase (Mg2+-dependent, Na+ + K+-activated ATP phosphohydrolase, EC 3.6.1.3), the turnover number of the enzyme, and the kinetic parameters for the ATP-dependent ouabain-enzyme interaction were compared in canine brain, heart and kidney. Kinetic parameters were estimated using a graphical analysis of non-steady state kinetics. The protein recovery and the degree of increase in specific activity of (Na+ + K+)-ATPase and the ratio between (Na+ + K+)-ATPase and Mg2+-ATPase activities during the successive treatments with deoxycholate, sodium iodide and glycerol were dependent on the source of the enzyme. A method which yields highly active (Na+ + K+)-ATPase preparations from the cardiac tissue was not suitable for obtaining highly active enzyme preparations from other tissues. Apparent turnover numbers of the brain (Na+ + K+)-ATPase preparations were not significantly affected by the sodium iodide treatment, but markedly decreased by deoxycholate or glycerol treatments. Similar glycerol treatment, however, failed to affect the apparent turnover number of cardiac enzymes preparations. Cerebral and cardiac enzyme preparations obtained by deoxycholate, sodium iodide and glycerol treatments had lower affinity for ouabain than renal enzyme preparations, primarily due to higher dissociation rate constants for the ouabain.enzyme complex. This tissue-dependent difference in ouabain sensitivity seems to be an artifact of the purification procedure, since less purified cerebral or cardiac preparations had lower dissociation rate constants. Changes in apparent association rate constants were minimal during the purfication procedure. These results indicate that the presentyl used purification procedures may alter the properties of membrane (Na+ + K+)-ATPase and affect the interaction between cardiac glycosides and the enzyme. The effect of a given treatment depends on the source of the enzyme. For the in vitro studies involving purified (Na+ + K+)-ATPase preparations, the influence of the methods used to obtain the enzyme preparation should be carefully evaluated.
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PMID:Membrane (Na+ + K+)-ATPase of canine brain, heart and kidney. Tissue-dependent differences in kinetic properties and the influence of purification procedures. 14 5

(Na+ + K+)-ATPase activity is demonstrated in plasma membranes from pig mesenteric lymph nodes. After dodecyl sulfate treatment plasma membranes have an 18-fold higher (Na+ + K+)-ATPase activity, while their ouabain-insensitive Mg2+-ATPase is markedly lowered. A solubilized (Na+ +K+)-ATPase fraction, obtained by Lubrol WX treatment of the membranes, has very high specific activity (21 mumol Pi/h per mg protein). Concanavalin A has no effect on these partially purified (Na+ + K+)-ATPase, while inhibits (40%) this activity in less purified fractions which still contain Mg2+-ATPase activity.
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PMID:Studies of (Na+ + K+)-sensitive ATPase activity in pig lymphocytes. Effects of concanavalin A. 14 92

The activities of Ca2+, Mg2+-ATPase and Na+, K+-ATPase and the permeability of reconstituted human erythrocytes for Na and K ions were measured, using Ca2+-EGTA, Ca2+ATP and Ca2+-sodium citrate buffers. It was found that the increase in the Ca2+/chelate ratio caused stimulation of Ca2+, Mg2+- and Na+, K+-Atpases and an increase in the rate constants of ouabain--dependent 42K+ influx and 22Na+ efflux from the erythrocytes. The use of the Ca2+-sodium citrate system as a calcium buffer did not change the parameters of the functional state of erythrocyte membranes. The data obtained are discussed in terms of a possible role of calcium ions, which are bound to the inner surface of the erythrocyte membrane, in the regulation of the systems of active and passive transport of cations.
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PMID:[The effect of membrane-bound calcium on the activity of adenosine triphosphatase from erythrocytes and erythrocyte permeability for monovalent cations]. 14

Calcium transport from red cells was measured in seventeen patients with congenital or hereditary spherocytosis (HS). The efflux remained at a lower level in resealed ghost cells of patients than in normal cells both in the presence and absence of adenosine triphosphate (ATP). We studied the activities of Ca2+,Mg2+-ATPase, ouabain-sensitive Na+,K+-ATPase, Mg2+-ATPase and Ca2+-(spectrin-)ATPase in cell membranes prepared by washing the cells with hypotonic medium. The mean +/-SD Ca2+,Mg2+-ATPase/Mg2+-ATPase of HS patients was 3.34 +/- 1.06, and 2.81 +/- 0.42 in control subjects. Na+,K+-ATPase/Mg2+-ATPase was 2.38 +/- 0.38 in HS cells compared to 2.01 +/- 0.41 in normal cells. Ca2+-ATPase/Mg2+-ATPase of HS membranes was 0.57 +/- 0.18 and the control value 0.43 +/- 0.08. These data indicate calcium retention in the erythrocytes of HS patients in spite of increases in Ca2+,Mg2+-ATPase activity in the majority of patients.
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PMID:Calcium transport and adenosine triphosphatase activities of erythrocyte membranes in congenital spherocytosis. 14 26

The article deals with the influence of sodium dodensylsulfate, lubrol and also of inhibition of Na+,K+-ATPase and Mg2+-ATPase activities by N-ethyl malemid on the form of curves of erythrocyte membranes amperometric titration by Ag+. It is shown that changes in a conformational structure of proteins membranes under the influence of detergents results in the transformation of SH-group of type I to SH-groups of type II. A 70% fall of Na+,K+-ATPase activity has the same result. So, the form of the curves for titration of erythrocyte membranes sulphydryl groups may serve as an indicator to the morpholocial and functional state of the membranes protein part.
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PMID:[Influence of detergents and inhibition of Na+,K+-ATPase and Mg2+ATPase on erythrocyte membrane SH-groups]. 14 2

The regulation of adrenergic receptors in rat heart was measured in rats made hyperthyroid by injection with thyroxine and made hypothyroid by addition of propylthiouracil to the drinking water. Hyperthyroid rats display cardiac hypertrophy and a decrease in epididymal fat pad weight. The maximal beta-receptor level of ventricular membranes, as determined by (-)-[3H]dihydroalprenolol binding, was increased 60% by thyroxine treatment and decreased about 30% by propylthiouracil treatment. The affinity of the beta receptor was unchanged after thyroxine or propylthiouracil treatment. The maximal activity of the isoproterenol-stimulated adenylate cyclase (EC 4.6.1.1) varied with thyroid state in a manner parallel to the increase in beta-adrenergic binding sites. Thyroxine treatment also increases by 2-fold the beta receptors in isolated rat fat cells. Propylthiouracil treatment lowered the level of alpha receptors in heart by 30% as measured by [3H]dihydroergocryptine binding, but increased the affinity about 2.5-fold. The highest level of alpha receptors was seen in control hearts. These studies indicate that thyroxine may control the turnover of beta-adrenergic receptors in heart and fat cells and regulate physiological responses in these tissues via a hormone-hormone interplay system. Thyroxine treatment reduced the activity of the membrane-bound Mg2+-ATPase (EC 3.6.1.3) and 5'-mononucleotidase (EC 3.1.3.5) but appears to increase the activity of the (Na+ + K+)ATPase (EC 3.6.1.4).
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PMID:Hormone action at the membrane level. VIII. Adrenergic receptors in rat heart and adipocytes and their modulation by thyroxine. 14 63

The influence of sulfhydryl reagents on ATPase systems of rabbit sceletal muscles nuclei was studied. It is found that p-ChMB at low concentration similarly inhibits both Mg2+- and Mg2+, Ca2+-ATPases. p-ChMB at higher concentrations inhibits completely Mg2+, Ca2+-ATPase, while Mg2+- ATPase--only by 60%. N-EM is lesser specific inhibitor of SH-groups, than p-ChMB. The degree of nuclear ATPases inhibition by N-EM is practically identical. Using inhibitory analysis, two hypes of skeletal muscles nuclei SH-groups are found: easily reacting with N-EM, and those reacting with N-EM at more high concentrations, which are essential for ATPase ATP-hydrolysing activity. ATP defends Mg2+, Ca2+-ATPase, but not the Mg2+-ATPase from N-EM inhibitory action. Cysteine completely eliminates the inhibitory effect of p-ChMB on Mg2+-ATPase but only 40% on MG2+, Ca2+-ATPase. Mg2+, Ca2+-ATPase of nuclei is more sensitive to the sulfhydryl venoms action than Mg2+-ATPase.
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PMID:[Effect of SH-reagents on ATPase systems of rabbit skeletal muscle nuclei]. 14 67


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