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)

Daily administration of d,l isoproterenol-HCl (5 mg/kg) in rats for periods of 14-21 days results in marked cardiac hypertrophy and a decrease in cardiac actomyosin ATPase activity. Actomyosin suspensions (ionic strength 0.08) from right and left ventricles showed average decreases in ATPase activity of 37.1% (p less than 0.005) and 35.7% (p less than 0.05), respectively, for animals treated with isoproterenol for 14 days. Isolated myofibrils from combined ventricular muscle of another group of animals that received the same isoproterenol treatment showed an average decrease in ATPase of 36.4% (p less than 0.0025). The later experiments also demonstrated that the decrease in ATPase activity was not Ca++ sensitive suggesting the lack of involvement of a change in the calcium regulatory factors (tropomyosin-troponin complex). In contrast to these findings, purified myosin from treated animals and actomyosin assayed under conditions which essentially reflect myosin ATPase activity uninfluenced by actin interaction (actomyosin in solution, ionic strength 0.6), did not demonstrate a change in ATPase from controls. It was concluded that the decrease in cardiac actomyosin ATPase in isoproterenol treated rats involved primarily a defect in actin or the interaction of actin with other components of the contractile protein complex.
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PMID:Characterization of the decreased ATPase activity of rat cardiac actomyosin in isoproterenol-induced cardiac hypertrophy. 15 67

Analyses of the binding of tropomyosin to muscle and Acanthamoeba actin by the use of Scatchard plots indicate that the binding exhibits strong positive cooperativity in the presence of Mg2+. The cooperative nature of the binding is not affected by the presence of 80 mm KCl, but appears to decrease somewhat in the presence of heavy meromyosin or subfragment-1. Heavy meromyosin, subfragment-1, and KCl each increase the binding affinity of actin for tropomyosin; depending on the experimental condition and the type of actin involved, the apparent binding constant, Kapp, is in the range of 1 to 4 x 10(6) M-1. Muscle actin cross-linked with glutaraldehyde failed to bind tropomyosin even when heavy meromyosin, subfragment-1, or KCl were added as inducers, although the cross-linked actin still markedly activated the heavy meromyosin ATPase.
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PMID:Cooperative binding of tropomyosin to muscle and Acanthamoeba actin. 15 26

Tropomyosin, one of the proteins regulating the sarcomere, was prepared from pig heart and rabbit skeletal muscles. The effect of these two different tropomyosins was studied between 0.5 and 10 mM of Mg2+ at a constant ATP concentration (1 mM) on reconstituted actomyosin prepared from pig heart myosin and rabbit skeletal actin. Cardiac and skeletal tropomyosin both activated the ATPase at low Mg2+ concentrations and inhibited it above 3 mM. The pig heart and rabbit skeletal tropomyosins which contain two isomers, alpha alpha and alpha beta, respectively has very similar effects on actomyosin ATPase.
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PMID:Effect of cardiac and skeletal tropomyosin on Mg2+-actomyosin ATPase. 16 Feb 49

1. A series of defined peptides which span the complete sequence were produced from troponin I isolated from white skeletal muscle of the rabbit. 2. Two peptides, CF1 (residues 64-133) and CN4 (residues 96-117) inhibited the Mg2+-stimulated adenosine triphosphatase of desensitized actomyosin. This inhibition was potentiated by tropomyosin and the Mg2+-stimulated adenosine triphosphatase of desensitized actomyosin. This inhibition, unlike that of troponin I and peptides derived from it, was not potentiated by tropomyosin. 4. The most active inhibitor, peptide CN4, was 45-75% as effective as troponin I when compared on a molar basis. The inhibitory peptide, CN4, and also whole troponin I were shown by affinity chromatography to interact specifically with actin. 5. A strong interaction with troponin C was demonstrated with peptide CF2 (residues 1-47), from the N-terminal region of troponin I. Somewhat weaker interactions were shown with peptides CN5 (residues 1-21) and with the inhibitory peptide CN4. 6. The significance of these interactions for the mechanisms of action of troponin I is discussed.
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PMID:The relationship between biological activity and primary structure of troponin I from white skeletal muscle of the rabbit. 17 35

A 35--70% ammonium sulfate fraction of smooth muscle actomyosin was prepared from guinea pig vas deferens. This fraction also contains a smooth muscle myosin kinase and a phosphatase that phosphorylates and dephosphorylates, respectively, the 20,000-dalton light chain of smooth muscle myosin. Phosphorylated and dephosphorylated smooth muscle myosin. Phosphorylated and dephosphorylated smooth muscle myosin were purified from this ammonium sulfate fraction by gel filtration, which also separated the kinase and the phosphatase from the myosin. Purified phosphorylated and dephosphorylated myosin have identical stained patterns after sodium dodecyl sulfate/polyacrylamide gel electrophoresis. They also have similar ATPase activities measured in 0.5 M KCl in the presence of K+-EDTA and Ca2+. However, the actin-activated myosin ATPase activity is markedly increased after phosphorylation. Moreover, the actin-activated ATPase activity of phosphorylated myosin is inhibited by the removal of Ca2+ in the absence of any added regulatory proteins. Dephosphorylation of myosin results in a decrease in the actin-activated ATPase activity. Skeletal muscle tropomyosin markedly increased the actin-activated ATPase activity of phosphorylated but not dephosphorylated myosin in the presence, but not in the absence, of Ca2+.
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PMID:Effect of phosphorylation of smooth muscle myosin on actin activation and Ca2+ regulation. 18 2

A human skeletal actin.tropomyosin.troponin complex was phosphorylated in the presence of [gamma-32 P]ATP, Mg2+, adenosine 3':5'-monophosphate (cyclic AMP) and cyclic AMP-dependent protein kinase (protein kinase). Phosphorylation was not observed when the actin complex was incubated in the absence of protein kinase or 1 microM cyclic AMP. In the presence of 10(-7) M Ca2+ and protein kinase 0.1 mole of [32P]phosphate per 196 000 g of protein was incorporated. This was two-fold higher than the [32P]phosphate content of a rabbit skeletal actin complex but two-fold lower than that of a bovine cardiac actin complex. At high Ca2+, 5.10(-5) M, little change in the phosphorylation of a human skeletal actin complex occurred. Phosphoserine and phosphothreonine were identified in the [32P]phosphorylated actin complex. Polyacrylamide gel electrophoresis in sodium dodecyl sulfate showed that 60% of the label was associated with the tropomyosin binding component of troponin. The inhibitory component of troponin contained 16% of the bound [32P]phosphate. Increasing the Ca2+ concentration did not significantly decrease the [32P]phosphate content of the phosphorylated proteins in the actin complex. No change in the distribution of phosphoserine or phosphothreonine was observed. Half maximal calcium activation of the ATPase activity of reconstitute human skeletal actomyosin made with the [32P] phosphorylated human skeletal actin complex was the same as a reconstituted actomyosin made with an actin complex incubated in the absence of protein kinase at low or high Ca2+.
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PMID:Phosphorylation of an actin.tropomyosin.troponin complex from human skeletal muscle. 20 9

Actin, myosin, and "native" tropomyosin (NTM) were separately isolated from chicken gizzard muscle and rabbit skeletal muscle. With various combinations of the isolated contractile proteins, Mg-ATPase activity and superprecipitation activity were measured. It was thus found that gizzard myosin and gizzard NTM behaved differently from skeletal myosin and skeletal NTM, whereas gizzard actin functioned in the same wasy as skeletal actin. It was also found that gizzard myosin preparations were often Ca-sensitive, that is, that the two activities of gizzard myosin plus actin without NTM were activated by low concentrations of Ca2+. The Mg-ATPase activity of a Ca-insensitive preparation of gizzard myosin was not activated by actin even in the presence of Ca2+. When Ca-sensitive gizzard myosin was incubated with ATP (and Mg2+) in the presence of Ca2+, a light-chain component of gizzard myosin was phosphorylated. The light-chain phosphorylation also occurred when Ca-insensitive myosin was incubated with gizzard NTM and ATP (plus Mg2+) in the presence of Ca2+. In either case, the light-chain phosphorylation required Ca2+. Phosphorylated gizzard myosin in combination with actin was able to exhibit superprecipitation, and Mg-ATPase of the phosphorylated gizzard myosin was activated by actin; the actin activation and superprecipitation were found to occur even in the absence of Ca2+ and NTM or tropomyosin. The phosphorylated light-chain component was found to be dephosphorylated by a partially purified preparation of gizzard myosin light-chain phosphatase. Gizzard myosin thus dephosphorylated behaved exactly like untreated Ca-insensitive gizzard myosin; in combination with actin, it did not superprecipitate either in the presence of Ca2+ or in its absence, but did superprecipitated in the presence of NTM and Ca2+. Ca-activated hydrolysis of ATP catalyzed by gizzard myosin B proceeded at a reduced rate after removal of Ca2+ (by adding EGTA), whereas that catalyzed by a combination of actin, gizzard myosin, and gizzard NTM proceeded at the same rate even after removal of Ca2+. However, addition of a partially purified preparation of gizzard myosin light-chain phosphatase was found to make the recombined system behave like myosin B. Based on these findings, it appears that myosin light-chain kinase and myosin light-chain phosphatase can function as regulatory proteins for contraction and relaxation, respectively, of gizzard muscle.
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PMID:Calcium sensitivity of contractile proteins from chicken gizzard muscle. 20 16

EDTA treatment of isolated plasma membranes from MF2S cells increased 1,000 fold the sensitivity of (Na+ + K+) ATPase activity to ouabain. The original sensitivity of the enzyme to the drug is recovered after addition of tropomyosin together with Ca++ ions to the treated membranes.
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PMID:[Role of tropomyosin in the sensitivity of (Na+ + K+) ATPase to ouabain]. 22 73

The degradation of rat cardiac myofibrils and their constituent proteins with a myosin-cleaving protease was studied. Electrophoretograms of the digestion products of myofibrils showed that myosin,M-protein, C-protein, and troponin were degraded, but actin and tropomyosin were not. Degradation of these constituents resulted in losses of the Mg2+-ATPase activity and its Ca2+-sensitivity of myofibrils. Incubation of myofibrils with the protease induced the release of alpha-actinin without degradation. Susceptibilities of myosin, actin, troponin, and alpha-actinin purified from rat and pig hearts to the protease were essentially identical to those of the assembled forms in myofibrils. Although the purified tropomyosin was readily degraded into five fragments with the protease, the tropomyosin assembled in myofibrils and actin-tropomyosin complex were insusceptible to the protease. Digestion of myosin in the filamentous state with the protease resulted in the disappearance of myosin heavy chain and light chain 2, producing two fragments having molecular weights of 130,000 and 94,000 which originated from the degradation of heavy chain. The Ca2+- and EDTA-ATPase activities of the degradation products remained unchanged during incubation for 22 h. The actin-activated ATPase activity of myosin was reduced by 30% during incubation for 6 h, and recovered to the original level on adding actin to give a ratio of actin to myosin of 2:1. The pH optima for degradation of myosin in the soluble and filamentous states were 8.5 and 7.0, respectively. The results indicate that cardiac myosin in the filamentous state was more readily degraded with the protease than the myosin in the soluble state.
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PMID:Degradation of rat cardiac myofibrils and myofibrillar proteins by a myosin-cleaving protease. 47 42

Rabbit alpha-tropomyosin was cleaved into two pieces at the cysteine residue of each chain. The products were separated by chromatography and characterized by amino acid analysis, molecular weight determination in benign and denaturing solvents, optical rotation and circular dichroism. When the cleavage reaction was carried out under mild conditions which preserve the two-chain structure there was considerable loss of alpha-helix in each segment. Thermal stability studies, monitored by optical rotation and circular dichroism, showed that the transition temperature of the N-terminal fragment at pH 7.6 was approximately 17 degrees C higher than that of the C-terminal fragment. In acid solutions there is little difference in the thermal stability of the two segments. The least stable part of the molecule is concluded to be between residues 133 and 205 and this includes the troponin-binding site. The relative stabilities found for segments of rabbit alpha-tropomyosin differ from recent published conclusions and this may be a result of the different methods used to study the loss of the alpha-helical conformaton. The two tropomyosin fragments, unlike the parent tropomyosin, do not inhibit actomyosin adenosinetriphosphatase when mixed with troponin. The fragments did not show any of the aggregation properties of tropomyosin and did not combine with actin. The N-terminal fragment did not complex with troponin but there was some evidence for an interaction between the C-terminal fragment and troponin.
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PMID:Stability of segments of rabbit alpha-tropomyosin. 61 6


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