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)

Localization and quantification studies were carried out on bay-scallop (Aequipecten irradians) striated-muscle troponin C- and troponin I-like proteins. Indirect immunofluorescence microscopy of scallop myofibrils stained with either rabbit anti-(scallop troponin I) or anti-(scallop troponin C) antibodies shows staining of all I-bands observed. The results of quantification studies using sodium dodecyl sulfate poly-acrylamide-gel electrophoresis of untreated scallop myofibrils, washed scallop myofibrils, and isolated scallop thin filaments indicate an actin/tropomyosin/troponin-C molar rationn of 7:1:1. The molar ratio for troponin I could not be determined in untreated myofibrils because of interfering bands; in washed myofibrils a value of 0.6 mol of troponin I/mol of tropomyosin was found. Purified scallop troponin C binds Ca2+ and interacts with scallop troponin I to relieve troponin I-induced inhibition of actomyosin ATPase. Although scallop troponin C is an acidic protein, it appears to be less acidic than troponin C from higher organisms. A calmodulin-like protein has been isolated from scallop striated muscle that activates bovine brain phosphodiesterase to the same extent as does brain calmodulin. Its amino acid composition and its electrophoretic mobility on alkaline 6 M-urea/polyacrylamide gels differs from that of scallop troponin C, and it appears not to be associated with thin filaments.
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PMID:The stoichiometry and location of troponin I- and troponin C-like proteins in the myofibril of the bay scallop, Aequipecten irradians. 624 69

1. Porcine cardiac native tropomyosin was phosphorylated by bovine cardiac 3':5'-cyclic AMP-dependent protein kinase. Most of the phosphate incorporation was observed in troponin I, the maximum of which was 0.7 mol of Pi per mol of troponin I. 2. In the presence of phosphorylated native tropomyosin, actomyosin ATPase activity was 15-40% lower than that in the presence of the unphosphorylated preparation at all calcium ion concentrations (1.5 x 10(-8) M-2.4 x 10(-5) M). Half-maximum activation of ATPase was obtained with a concentration of 7 x 10(-7) M Ca2+ (unphosphorylated) and 1.3 x 10(-6) M Ca2+ (phosphorylated), respectively. Maximum ATPase activity was reached with 3 x 10(-6) M Ca2+ (unphosphorylated) and 1.0 x 10(-5) M Ca2+ (phosphorylated). 3. Porcine cardiac troponin I isolated by affinity chromatography inhibited ATPase activity of desensitized actomyosin in the presence of tropomyosin. There was little difference between phosphorylated troponin I and a control preparation with regard to the inhibitory effect of ATPase activity. 4. Troponin C from rabbit skeletal muscle neutralized the inhibitory effect of troponin I. The minimum amount of troponin C required for complete neutralization was approximately equimolar to troponin I. The inhibitory effect of phosphorylated troponin I was neutralized by troponin C less effectively than that of unphosphorylated preparation.
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PMID:Effect of phosphorylation of porcine cardiac troponin I by 3':5'-cyclic AMP-dependent protein kinase on the actomyosin ATPase activity. 628 30

Glycerinated myocardial fibres treated with a detergent (Lubrol WX) and suspended in ATP salt solution produce half maximum isometric tension at pCa 6.2 (at pH 6.7). After addition of cyclic AMP (1-100 microM), the pCa required for half maximum activation is 5.9. c-AMP in concentrations of 1-100 microM induces a dose dependent inhibition (up to 40% at pCa6), and this effect can be amplified by the phosphodiesterase inhibitor IBMX (3-isobutyl-1-methylxanthine) 10(-4) M. The effect is similar in presence and absence of sodium fluoride 10 mM. Since in detergent treated skinned fibres the cell membrane and the sarcoplasmic reticulum are extracted and since the Ca2+ ion concentration was kept constant and buffered, we propose that c-AMP does not act via the cell membrane or the sarcoplasmic reticulum, but via phosphorylation of troponin I. The latter is the only component which becomes phosphorylated in skinned fibres during c-AMP induced relaxation, an effect which is also responsible for the inhibition of actomyosin ATPase at constant Ca2+ ion concentration (cf. Ray and England 1976).
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PMID:Cyclic AMP inhibits contractility of detergent treated glycerol extracted cardiac muscle. 628 42

Adrenergic stimulation alters functional dynamics of the heart by mechanisms most likely involving cyclic AMP (cAMP)-dependent protein phosphorylation. In vitro studies indicate that the myofibrils and sarcoplasmic reticulum (SR) may act as effectors of the adrenergic stimulation. cAMP-dependent phosphorylation of troponin I (TnI), one of the regulatory proteins of cardiac myofibrils, results in a decreased steady-state affinity of troponin C (TnC) for calcium, an increase in the off-rate for Ca2+ exchange with TnC, and a rightward shift of the relation between free Ca2+ and myofibrillar force or ATPase. Phosphorylation of phospholamban, a regulatory protein of cardiac SR, results in an increased velocity of Ca2+ transport by SR vesicles, an increased affinity of the transport protein for Ca2+, and an increased turnover of elementary steps of the ATPase reaction. These in vitro findings support the hypothesis that the inotropic response of the heart to catecholamine stimulation involves phosphorylation of TnI and phospholamban. Our in vivo studies with perfused rabbit hearts show that during the peak of the inotropic response to isoproterenol there is a simultaneous phosphorylation of TnI and an 11,000-dalton protein in the SR, most likely the monomeric form of phospholamban.
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PMID:Coordination of cardiac sarcoplasmic reticulum and myofibrillar function by protein phosphorylation. 629 80

Myocardial function can be modulated at the level of the sarcolemma, the intracellular Ca2+ stores, and the myofilaments. A way of following myofibrillar modulation of mechanochemical activity is by studying the Ca2+-dependent activation of myofibrils. In this study, the role of Mg2+ in the Ca2+ activation of myofibrillar ATPase was evaluated. The concentrations of both free Ca2+ and free Mg2+ were varied at a given concentration of MgATP (3.16 mM), ionic strength (0.12), and pH 7.0. The experimental ATPase-vs.-Ca2+ data were fit to the model-independent Hill equation and to Tawada's model of intertropomyosin cooperation. In the micromolar range, Mg2+ did not affect the Ca2+ sensitivity, whereas it was reduced at high Mg2+ (5 mM), corresponding to a shift of the activation curve to higher Ca2+ concentrations. Positive cooperativity (n = 2.4) and ATPase activity at saturating Ca2+ concentrations were affected only at low Mg2+. At 0.032 mM Mg2+, the positive cooperation was partially lost (n = 1.3), and maximum ATPase was reduced by 23%. The consequences of a change in the activation curves for the mechanogram are shown. The influence of other modulatory mechanisms on the activation properties was also analyzed on the basis of the Hill equation and the intertropomyosin cooperation model. Acute changes in contractility can arise from changes in the intracellular pH, in sarcomere length, and from phosphorylation of troponin I. Long-term modifications of cardiac performance involve genetic expression of different myosin isoenzymes. The relevance of these different modulatory mechanisms for myocardial function is shown.
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PMID:Calcium-dependent activation of cardiac myofibrils. The mechanisms that modulate myofibrillar ATPase and tension and their significance for heart function. 630 87

It was shown that 3,3'-dipropylthiocarbocyanine iodide diS-C3-(5) can be used as a fluorescent probe for registration of conformational changes in calmodulin and troponin C, as well as for determination of concentrations of these Ca-binding proteins in experimental samples. The sensitivity of the method (10(-7) M) is only 5 times less than that of determination of calmodulin by phosphodiesterase and by 1 or 2 orders of magnitude more than that of other techniques based on conformational changes of the protein. The spectral parameters of the fluorescent probe allow to conduct the measurements in turbid media and in the presence of many other optically active substances. Evidence is given testifying the promiscuity of the use of this approach to the study of conformational changes in calmodulin under the action of Ca2+, Mg2+, monovalent cations, temperature and target proteins (troponin I, phosphodiesterase). using phosphodiesterase and Ca-ATPase, it was shown that under certain conditions diS-C3-(5) as well as other amphypathic compounds can modify the activity of calmodulin-dependent enzymes.
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PMID:[Use of 3,3'-dipropylthiodicarbocyanine iodide diS-C3-(5) for the study of conformational changes and detection of Ca-binding proteins]. 632 70

We used a recently developed preparation of calcium-tolerant isolated rat cardiac ventricular cells to investigate certain aspects of hormone-mediated protein phosphorylation in heart tissue. Isoproterenol or dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP) promoted the phosphorylation of at least 13 proteins and promoted the dephosphorylation of a single protein of relative molecular weight (Mr) 21,000, whose phosphorylation appeared to be stimulated by insulin. The isoproterenol-induced protein phosphorylations reached maximum levels for most proteins within 5 min at slightly different rates. However, when excess propranolol was added to the cells after exposure to isoproterenol, there appeared to be two major patterns of dephosphorylation: proteins that remained fully phosphorylated after propranolol addition, exemplified by proteins tentatively identified as troponin I and C-protein, and proteins that were rapidly dephosphorylated after propranolol, exemplified by phospholamban, the modulator of the sarcoplasmic reticulum calcium-dependent ATPase. The Mr 21,000 protein was rapidly dephosphorylated in response to isoproterenol and was rephosphorylated after addition of propranolol. This protein remains unidentified; it is not the Mr 19,000 myosin light chain whose phosphorylation state was unaffected by isoproterenol. This preparation of isolated heart cells provides a convenient way to investigate the biochemical effects resulting from exposure of the heart to hormones and can separate direct hormonal effects from those resulting from changes in contractility or heart rate.
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PMID:Hormonal regulation of protein phosphorylation in isolated rat heart cells. 632 6

Myosin and actin competition tests indicated the presence of both thin-filament and myosin-linked Ca2+-regulatory systems in pig aorta and turkey gizzard smooth-muscle actomyosin. A thin-filament preparation was obtained from pig aortas. The thin filaments had no significant ATPase activity [1.1 +/- 2.6 nmol/mg per min (mean +/- S.D.)], but they activated skeletal-muscle myosin ATPase up to 25-fold [500 nmol/mg of myosin per min (mean +/- S.D.)] in the presence of 10(-4) M free Ca2+. At 10(-8) M-Ca2+ the thin filaments activated myosin ATPase activity only one-third as much. Thin-filament activation of myosin ATPase activity increased markedly in the range 10(-6)-10(-5) M-Ca2+ and was half maximal at 2.7 x 10(-6) M (pCa2+ 5.6). The skeletal myosin-aorta-thin-filament mixture gave a biphasic ATPase-rate-versus-ATP-concentration curve at 10(-8) M-Ca2+ similar to the curve obtained with skeletal-muscle thin filaments. Thin filaments bound up to 9.5 mumol of Ca2+/g in the presence of MgATP2-. In the range 0.06-27 microM-Ca2+ binding was hyperbolic with an estimated binding constant of (0.56 +/- 0.07) x 10(6) M-1 (mean +/- S.D.) and maximum binding of 8.0 +/- 0.8 mumol/g (mean +/- S.D.). Significantly less Ca2+ bound in the absence of ATP. The thin filaments contained actin, tropomyosin and several other unidentified proteins. 6 M-Urea/polyacrylamide-gel electrophoresis at pH 8.3 showed proteins that behaved like troponin I and troponin C. This was confirmed by forming interspecific complexes between radioactive skeletal-muscle troponin I and troponin C and the aorta thin-filament proteins. The thin filaments contained at least 1.4 mumol of a troponin C-like protein/g and at least 1.1 mumol of a troponin I-like protein/g.
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PMID:Calcium ion-regulated thin filaments from vascular smooth muscle. 644 98

Cardiac hypertrophy induced by thyrotoxic stress leads to an increase in the rate of force development, velocity of shortening, tension-dependent heat generation, and myosin ATPase activity. We did studies to see whether alterations in covalent phosphorylation of myofibrillar proteins correlate with these changes. The protein preparations were isolated from control and thyrotoxic hearts of male albino rabbits freeze-clamped in situ. We measured myofibrillar ATPase, and the covalent phosphate content of ventricular myosin 19,000 (mol wt) light chain (P-light chain) and troponin I (TnI). The myofibrillar ATPase activity was increased 2-fold in the thyrotoxic preparations with no change in the level of myofibrillar phosphorylation. The covalent phosphate content of TnI was 1.21 +/- 0.09 mol P/mol TnI in control hearts and 1.14 +/- 0.04 mol P/mol TnI in thyrotoxic hearts. The covalent phosphate content of the light chain fraction was 0.41 +/- 0.06 mol P/mol P-light chain in control hearts and 0.37 +/- 0.04 mol P/mol P-light chain in thyrotoxic hearts. The dependence of the normalized myofibrillar ATPase on free calcium concentration was the same in control and thyrotoxic preparations. Thus the mechanical, thermal, and biochemical changes found in hearts from thyrotoxic animals probably occur with no change in phosphorylation of TnI or myosin light chains.
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PMID:Phosphorylation and adenosine triphosphatase activity of myofibrils from thyrotoxic rabbit hearts. 645 Jun 50

Twelve peptide analogs of the actomyosin ATPase inhibitory region of rabbit skeletal troponin I (Tn-I) have been synthesized by the solid phase method and tested for biological activity in both actomyosin and acto-S1(A1) systems. Acto-S1(A1) is a cleaner and more facile system and we found no important discrepancies in the results for the two systems. These studies indicate that the sequence 105 to 114 is necessary for inhibition and that the inhibition is on the order of that reported for the 21-residue cyanogen bromide fragment of Tn-I (residues 96 to 116). We have shown the importance of lysine 105 and that of a bulky side chain at position 114 to this inhibition. Both the high activity of peptides containing the sequence 105 to 114 compared to Tn-I (45% on a molar basis) and the previously demonstrated tropomyosin specificity of this activity indicate that the relative inhibitory activity of these peptides is applicable to the discussion of the inhibitory activity of Tn-I. We have proven that actin concentration is a significant factor determining the extent of inhibition of both Tn-I and the peptides. We have also established that the charges on alpha-amino and alpha-carboxyl groups of a peptide, which do not appear in the parent protein, can modify the activity of the peptides. This must be taken into account when extrapolating from the activity of a peptide to the activity of the protein.
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PMID:Synthetic studies on the inhibitory region of rabbit skeletal troponin I. Relationship of amino acid sequence to biological activity. 645 20


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