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)

1) The contractile system consists of thick and thin filaments arranged side by side in a double network of hexagonal cross-section. 2) The thick filaments are principally made up of myosin and the thin ones of actin, tropomyosin and troponin. 3) Myosin is an enzyme catalysing the hydrolysis of ATP; actin increases the specific activity of this enzyme, converting it from a Ca+2 sensitive ATPase to a Mg+2 sensitive ATPase. 4) Hydrolysis of the last phosphoryl group of adenosine triphosphate (ATP) salts is the energy source for muscle contraction. 5) The adenosine diphosphate (ADP) salts, formed by ATP splitting, are rephosphorylated and reinjected into the myofibril.
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PMID:Ultrastructure of the contractile system of striated skeletal muscle and the processes of muscular contraction. I. Ultrastructure of the myofibril and source of energy. 76 91

The interaction of myosin and actin is by intracellular Ca2+ concentration, which in turn is controlled by the sarcoplasmic reticulum. In muscle--including cardiac muscle--of vertebrates, and some invertebrates, the site of Ca2+ control is in the thin, actin-containing filaments. These filaments contain tropomyosin and troponin; the latter is a complex of three subunits. When Ca2+ combines with troponin C, the Ca-binding subunit, a shift occurs in the position of tropomyosin that makes it possible for the myosin heads to bind to actin. This process is inhibited by a conformational change in troponin C, resulting in the release of the troponin complex from one of the binding sites on the thin filament. This process exhibits cooperative aspects which have been analyzed in terms of the Ca-binding process and the effect of Ca2+ on actomyosin ATPase activity.
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PMID:Excitation-contraction coupling--cardiac muscle events in the myofilament. 77 Feb 1

The topology of troponin, the calcium binding regulatory protein in muscle, has been studied by cross-linking with different length dimethylimido esters. The results show that the three components of troponin are close to each other and that the troponin-I and -T are preferentially cross-linked being 0.6 nm or less apart. The largest cross-linked product is a complex which corresponds in molecular weight to the native troponin complex of 1 mol of each of the three components. Cross-linked troponin has lost the ability to make the actomyosin ATPase calcium sensitive although it does bind to actin-tropomyosin and tropomyosin, and it binds calcium normally. No effect of calcium on cross-linking could be detected.
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PMID:Cross-linking of troponin with dimethylimido esters. 81 Dec 52

1. Changes of structural proteins in experimental and human myocardial infarction were studied by the determination of myosin- and actomyosin-ATPase activities and gel electrophoretic analysis in the presence of sodium dodecyl sulfate (SDS). 2. In animal experiments using dogs, the relative amounts of myosin and alpha-actinin decreased at 24 to 48 hours after coronary ligation, became lowest at 72 hours, and remained at this level for 2 weeks and returned to almost normal value at 28 days. 3. Myosin- and actomyosin-ATPase activities decreased rapidly during 24 to 48 hours after ligation with temporary increase in their activities in the initial stage of ischemia and followed the similar time course as that of the amounts of myosin and alpha-actinin. 4. SDS gel electrophoretic analysis of structural proteins of infarcted tissues of the human hearts obtained from 5 cadavers showed also marked decrease of the contents of myosin and alpha-actinin with relative preservation of actin, tropomyosin and troponin-T.
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PMID:Changes of cardiac structural proteins in myocardial infarction. 92 15

The flexible polymer of plasmodium actin (Mg-polymer) combines with muscle native tropomyosin up to a weight ratio of actin: tropomyosin:troponin = 6:1:1. Mg-polymer which combined with muscle native tropomyosin undergoes a conformational change when the Ca2+ concentration of the solution is decreased by adding 0.5 mM ethylene glycol bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA): the viscosity of the solution increases by 50% and its ATPase activity decreases to about 20% of the original value, which suggests that the structure of Mg-polymer becomes more rigid. This change is reversible with respect to the Ca2+ concentration in the solution. The threshold concentration of Ca2+ for the conformational change is about 10(-6) M. The possible role of this transformation in vivo is discussed.
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PMID:Conformational changes induced in plasmodium actin polymer by Ca2+ in the presence of muscle native tropomysin. 93 66

Immunological methods, in parellel with measurement of ATPase activity, have been used to characterize the reactions of antibodies specific for light chains with myosin and its water-soluble proteolytic subfragments, heavy meromyosin (HMM) and subfragment 1 (HMM S-1). Antiserum to the 5,5'-dithiobis(2-nitro-enzoic acid) (DTNB) light chain undergoes a precipitation reaction with all of the enzyme species, in which half of the homologous light chain is selectively dissociated. The results suggest that the incomplete dissociation reflects the way in which the light chain is bound, rather than the existence of two distinct species of DTNB 1.c. Little reaction was observed with antisera to alkali-released light chains, indicating that these components in myosin and the subfragments are either largely buried or else conformationally different from the isolated light chains used as immunogens. None of the antisera produced significant changes in Ca2+- or EDTA-ATPase activities. Moreover, calcium regulation through the troponin-tropomyosin system was unaffected by removal of DTNB 1.c. from myosin, as well as from the subfragments. The absolute level of actin-activated ATPase activity was, however, consistently lower in the presence of light chain antisera (or purified IgG and antibody) than in aqueous buffer or nonimmune serum. For both alkali and DTNB 1.c. antisera, this loss in activity seemed to result from steric hindrance of actin binding by antibody bound to undissociated light chain. Experimental conditions which would be expected to weaken such an antigen-antibody interaction, as well as the use of monovalent Fab in place of IgG, decreased the inhibition of activity. Altogether the activity measurements suggest that the light chains, particularly DTNB 1.c., are probably not integral parts of either the hydrolytic or actin-binding sites.
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PMID:An immunological approach to the role of the low molecular weight subunits in myosin. II. Interaction of myosin and its subfragments with antibodies to the light chains. 110 50

According to recent views the active troponin (Tn) complex consists of three components distinguishable by their ability to bind Ca2+ (TnC), to combine with troponyosin (TnT), and to inhibit actomyosin ATPase with ot without Ca2+ (TnI). Addition of Tn to an actin-myosin-tropomyosin system produceas a Ca2+ requirement for ATPase activity. Recent developments bearing on the mechanism both in vitro and in vivo are reviewed in order to correlate biochemical, physiochemical, electron microscopic, and physiological findings. The use of various combination of isolated components considerably helps in pinpointing changes that occur within components (conformational changes) and in the relative positions of interacting moieties. Available data on differences between the skeletal and cardiac system are also discussed.
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PMID:The regulatory system of the actin-myosin interaction. 110 43

Studies of the interaction between actin and myosin subfragment 1 (S1) in solution have shown that the association reaction takes place in at least two steps. Initially the association is relatively weak to form a complex called the A state which can then isomerize to the R state. The rate and equilibrium constants for the isomerization have been measured and are shown to depend upon the nucleotide bound to the S1 ATPase site; with ATP bound the A state is preferred but as ATP is hydrolysed and the products are sequentially released then the complex gradually shifts to the A state. An extensive series of experiments have characterized the A-to-R isomerization both in solution and in contracting muscle fibres and have shown it to be closely associated with the key events in the ATP-driven contraction cycle: the conformational change from the A to the R state can be monitored by fluorescent probes on either actin or the nucleotide; the isomerization can be perturbed by increases in hydrostatic pressure; the actin-induced acceleration of the rate of product release from myosin is coupled to the A-to-R isomerization; tropomyosin may control actin and myosin interaction by controlling the isomerization step and finally pressure perturbations of contracting muscle fibres shows there to be a close coupling between the isomerization of acto.S1 and the force generating event of muscle contraction.
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PMID:The actomyosin ATPase: a two-state system. 135 Dec 98

Cleavage of caldesmon with chymotrypsin yields a series of fragments which bind both calmodulin and actin and inhibit the binding of myosin subfragments to actin and the subsequent stimulation of ATPase activity. Several of these fragments have been purified by cation exchange chromatography and their amino-terminal sequences determined. The smallest fragment has a molecular mass of about 7.3 kDa and extends from Leu597 to Phe665. This polypeptide inhibits the actin-activated ATPase of myosin S-1; this inhibition is augmented by smooth muscle tropomyosin and relieved by Ca(2+)-calmodulin. The binding of the 7.3-kDa fragment to actin is competitive with the binding of S-1 to actin. Thus, this polypeptide has several of the important features characteristic of intact caldesmon. However, although an intact caldesmon molecule covers between six and nine actin monomers, the 7.3-kDa fragment binds to actin in a 1:1 complex. Comparison of this fragment with others suggests that a small region of caldesmon is responsible for at least part of the interaction with both calmodulin and actin.
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PMID:Localization and characterization of a 7.3-kDa region of caldesmon which reversibly inhibits actomyosin ATPase activity. 138 4

Caldesmon inhibition of actin-tropomyosin activation of myosin MgATPase activity was investigated. greater than 90% inhibition of ATPase activation correlated with 0.035-0.1 caldesmon bound per actin monomer over a wide range of conditions. Caldesmon inhibited sheep aorta actin-tropomyosin activation of skeletal muscle heavy meromyosin (HMM) by 85%, but had no effect on the binding affinity of HMM.ADP.Pi to actin. At ratios of 2 and 0.12 subfragment 1 (S1):1 actin, addition of caldesmon inhibited the ATPase activation by up to 95%, but did not alter the fraction of S1.ADP.Pi associated with actin-tropomyosin. We concluded that caldesmon inhibited actomyosin ATPase by slowing the rate-limiting step of the activation pathway. At concentrations comparable to the ATPase measurements, S1 displaced caldesmon from native thin filaments both in the absence (rigor) and the presence of MgATP. We therefore concluded that caldesmon could displace S1.ADP.Pi from actin-tropomyosin only under exceptional circumstances. An expressed mutant of caldesmon comprising just the C-terminal 99 amino acids bound actin 10 times weaker than whole caldesmon but otherwise inhibited actin-tropomyosin activation with the same potency and same mechanism as intact caldesmon. Thus, the entire inhibitory function of caldesmon resides in its extreme C terminus.
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PMID:Inhibition of actin-tropomyosin activation of myosin MgATPase activity by the smooth muscle regulatory protein caldesmon. 138 96


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