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:3.6.4.1 (myosin ATPase)
1,140 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The cyclic peptide phalloidin, one of the toxic components of Amanita phalloides prevented the drop of viscosity of F-actin solutions after the addition of 0.6 M KI and inhibited the ATP splitting of F-actin during sonic vibration. The data concerning ATP splitting are consistent with the assumption (a) that only 1 out of every 3 actin units of the filaments needs to be combined with phalloidin in order to suppress the contribution of these 3 actins to the ATPase activity of the filament and (b) that all actin units of the filaments can combine with phalloidin with a very high affinity. -halloidin did not only stabilize the actin-actin bonds in the F-actin structure but it also increased the rate of polymerization of G-actin to F-actin. The ability of F-actin to activate myosin ATPase was not affected by phalloidin. The tropomyosin-troponin complex did not prevent the stabilizing effect of phalloidin on the F-actin structure.
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PMID:Interaction of actin with phalloidin: polymerization and stabilization of F-actin. 12 84

The simplest interacting unit of actomyosin, viz., single myosin heads (subfragment 1) with actin monomers, has been studied at physiological ionic strength, by isolating the actin molecules from each other on a solid support. The interaction is characterized by a binding constant of 10(5) to 10(6) M-1 in the temperature range 4-30degrees C. It is endothermic with a standard enthalpy of 24 +/- 10 kcal mol-1, and a standard entropy of 110 +/- 40 eu. It is thus, like many protein-protein association processes, entropy-driven. Despite the high affinity of the association, which is comparable in its binding constant to that of subfragment 1 with F-actin, there is only very small activation of myosin ATPase. The ionic-strength dependence of the interaction shows unusual features. Binding of the proteins of the relaxing system to the monomeric actin was also examined: troponin binds both in the presence and absence of calcium ions, but neither tropomyosin nor the tropomyosin-troponin complex was found to bind significantly. Monomeric actin has also been examined as a function of ionic strength by spectroscopic methods; it appears that conformational differences between the G and the F state are the consequence of polymerization, and not of the change in ionic strength required to being the conversion about.
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PMID:The interaction of actin monomers with myosin heads and other muscle proteins. 13 85

The immunogenicity of smooth muscle actin is increased by ageing at 4 degrees for at least a week. Rabbits lacking natural smooth muscle antibodies were injected with 1 mg of aged purified actin in adjuvant. Fourteen out of thirty-six rabbits produced serum antibodies which precipitated with actin solution, but not with smooth muscle tropomyosin, myosin, light or heavy meromyosin or with other unidentified non-actin proteins in crude extracts. Analysis of crude actin extract before and after precipitation by antiserum (i) by Sephadex G-200 chromatography and (ii) for its stimulating effect on myosin ATPase activity showed that actin was selectively removed. The precipitate itself, analysed on SDS-polyacrylamide gel, showed one band in the actin position, and otherwise only bands representing immunoglobulins. The antiserum also inhibited the ability of actin to stimulate myosin ATPase activity, and prevented polymerization of G-actin to F-actin, as shown by viscosity and EM studies. On immunoflouresence with cryostat tissue sections or cell cultures, anti-actin serum stained smooth muscle fibres and many non-muscle cells, in the latter staining the microfilaments. The staining was prevented by absorbing the antiserum with actin (16 mug per 5 mul serum), and was abolished by pretreatment of the cells with cytochalasin B. No species specificity was demonstrated for these anti-actin antibodies.
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PMID:The specificity of anti-actin serum. 13 24

Reconstituted thin filaments (the actin-tropomyosin-leiotonin complex) of chicken gizzard were cross-linked with glutaraldehyde either in the presence or absence of Ca2+. The ability of resultant thin filaments to activate myosin ATPase was 'frozen' in the activated or inactivated state, respectively. This result clearly indicates the existence of actin-linked regulation in smooth muscle.
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PMID:'Freezing' of the calcium-regulated structures of gizzard thin filaments by glutaraldehyde. 15 56

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

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

The movement of reconstituted thin filaments over an immobilized surface of thiophosphorylated smooth muscle myosin was examined using an in vitro motility assay. Reconstituted thin filaments contained actin, tropomyosin, and either purified chicken gizzard caldesmon or the purified COOH-terminal actin-binding fragment of caldesmon. Control actin-tropomyosin filaments moved at a velocity of 2.3 +/- 0.5 microns/s. Neither intact caldesmon nor the COOH-terminal fragment, when maintained in the monomeric form by treatment with 10 mM dithiothreitol, had any effect on filament velocity; and yet both were potent inhibitors of actin-activated myosin ATPase activity, indicating that caldesmon primarily inhibits myosin binding as reported by Chalovich et al. (Chalovich, J. M., Hemric, M. E., and Velaz, L. (1990) Ann. N. Y. Acad. Sci. 599, 85-99). Inhibition of filament motion was, however, observed under conditions where cross-linking of caldesmon via disulfide bridges was present. To determine if monomeric caldesmon could "tether" actin filaments to the myosin surface by forming an actin-caldesmon-myosin complex as suggested by Chalovich et al., we looked for caldesmon-dependent filament binding and motility under conditions (80 mM KCl) where filament binding to myosin is weak and motility is not normally seen. At caldesmon concentrations > or = 0.26 microM, actin filament binding was increased and filament motion (2.6 +/- 0.6 microns/s) was observed. The enhanced motility seen with intact caldesmon was not observed with the addition of up to 26 microM COOH-terminal fragment. Moreover, a molar excess of the COOH-terminal fragment competitively reversed the enhanced binding seen with intact caldesmon. These results show that tethering of actin filaments to myosin by the formation of an actin-caldesmon-myosin complex enhanced productive acto-myosin interaction without placing a significant mechanical load on the moving filaments.
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PMID:The effects of smooth muscle caldesmon on actin filament motility. 142 47

Recently, one of the authors (K.I.) and other investigators reported that myosin light chain (MLC) of smooth muscle (gizzard, arterial and tracheal) was diphosphorylated by myosin light chain kinase (MLCK) and that diphosphorylated myosin showed a marked increase in the actin-activated myosin ATPase activity in vitro and ex vivo. In this study, we prepared myosin, actin, tropomyosin (human platelet), MLCK (chicken gizzard) and calmodulin (bovine brain) and demonstrated diphosphorylation of MLC of platelet by MLCK in vitro. Our results are as follows. (1) Platelet MLC was diphosphorylated by a relatively high concentration (greater than 20 micrograms/ml) of MLCK in vitro. As a result of diphosphorylation, the actin-activated myosin ATPase activity was increased 3 to 4-fold as compared to the monophosphorylation. (2) Both di- and monophosphorylation reactions showed similar Ca2+, KCl, MgCl2-dependence. Maximal reaction was seen at [Ca2+] greater than 10(-6) M, 60 mM KCl and 2 mM MgCl2. This condition was physiological in activated platelets. (3) Di- and monophosphorylated myosin showed similar Ca2+, KCl-dependence of ATPase activity but distinct MgCl2-dependence. Diphosphorylated myosin showed maximal ATPase activity at 2 mM MgCl2 and monophosphorylated myosin showed a maximum at 10 mM MgCl2. (4) The addition of tropomyosin stimulated actin-activated ATPase activity in both di- and monophosphorylated myosin to the same degree. (5) ML-9, a relatively specific inhibitor of MLCK, inhibited the aggregation of human platelets induced by thrombin ex vivo in a dose-dependent manner. Moreover, this drug also partially inhibited both di- and monophosphorylation reactions and actin-activated ATPase activity. On the other hand, H-7, a synthetic inhibitor of protein kinase C, had little effect on the aggregation of human platelets induced by thrombin ex vivo. From these results, we conclude that diphosphorylation of platelet myosin by MLCK may play an important role in activated platelets in vivo.
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PMID:Diphosphorylation of platelet myosin by myosin light chain kinase. 153 1

We define conditions under which the two C-terminal residues of actin, Cys-374 and Phe-375, can be selectively removed by proteolysis with trypsin. This modification had little effect on the secondary structure of actin detected by Fourier-transform infrared spectroscopy. However, removing these residues caused small but significant decreases in the critical concentration of actin, in its ability to activate myosin ATPase, and in its interaction with tropomyosin and troponin. Removing residues 374-375 caused dramatic changes in the actin filament as seen by electron microscopy. The filaments had a much greater and more irregular curvature and were intertwined into disordered multifilament bundles. Removing 374-375 also significantly lowered the flow viscosity of filamentous-actin solutions. These data suggest an increase in the flexibility and fragility of the filament, supporting the idea that the C-terminus forms one of the major intermonomer contacts in the filament.
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PMID:Removing the two C-terminal residues of actin affects the filament structure. 173 27

Cardiac myofibrils from cardiomyopathic hamsters exhibit elevated Mg2+ ATPase activity and a parallel upward shift of the calcium ATPase dose response curve. To explore the mechanism, myofibrils from control and cardiomyopathic hamster hearts were incubated with isolated troponin-tropomyosin complex (Tn.Tm) from cardiomyopathic and control hamster or from dog hearts. Tn.Tm from control hamster or dog hearts restored normal Mg2+ ATPase activities to myofibrils from myopathic hearts. However, the maximum ATPase response to calcium stimulation was less in cardiomyopathic myofibrils compared to controls, even when control Tn.Tm was included. Electrophoretic patterns of Tn.Tm from myopathic and control hearts were similar. Electrophoresis of the hamster myofibrils mixed with dog cardiac Tn.Tm and then washed demonstrated binding of this complex to myopathic myofibrils. To further confirm that the incubation experiments resulted in binding, 125I troponin-tropomyosin was cross-hybridized with myofibrils, extensively washed, and then analyzed enzymatically and autoradiographically. Autoradiograms demonstrated similar percent binding of 125I Tn.Tm to all myofibrillar preparations and enzymatic effects like those found using cold Tn.Tm. These studies suggest that Tn.Tm from cardiomyopathic hearts inhibits Mg2+ myofibrillar ATPase activity to a lesser degree than Tn.Tm from control hearts. Decreased stimulation by calcium in myopathic preparations may be due to abnormalities in troponin-tropomyosin and/or to the decreased myosin ATPase activity observed previously.
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PMID:Troponin-tropomyosin abnormalities in hamster cardiomyopathy. 214 67


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