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)

It is shown that smooth muscle actin preparations, produced with the help of techniques described in literature, have contaminations of tropomyosin and proteins with the molecular weight of 250 000, 80 000 and 18 000. The composition of contaminations depends on the method of preparation and conditions of dissociation of native actomyosin material. A method is proposed for actin separation from acetone-treated actomyosin followed by salting out with 50 mM MgCl2. Gel-electrophoresis in the presence of Na-dodecylsulphate has shown that the actin preparations are homogeneous and have the same cofactor activity for the myosin ATPase as actin from the rabbit skeletal muscle. It is supposed that in the cytoplasm of smooth muscle cells as well as in the non-muscle ones there is a considerable part of actin is the monomer form. It gets easily lost in the process of fibrillar actin separation. This may account for low actin output in spite of its relatively high contents in smooth muscles.
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PMID:[Features of the preparation and estimation of homogeneity and native state of smooth muscle actin]. 713 7

Actin filaments partially cross-linked with ANP (N-(4-azido-2-nitrophenyl)-putrescine between Gln-41 and Cys-374 on adjacent monomers in the long-pitch helix were depolymerized and fractionated into pools of longitudinal cross-linked dimers (s(o)20,w = 5.55 +/- 0.22 S), trimers (s(o)20,w = 6.93 +/- 0.12 S), and higher-order oligomers. Competition binding experiments of myosin subfragment (S1) to cross-linked dimers in the presence of pyrenyl G-actin revealed about 2 orders of magnitude stronger binding of the first than that of the second S1 molecule to actin dimer. Under similar conditions the unpolymerized cross-linked actin species activated the MgATPase of S1 only severalfold compared to 70-fold activation by F-actin. The cross-linked dimers, trimers, and oligomers were polymerized into filaments by MgCl2 faster than un-cross-linked actin. In electron micrographs these filaments appeared sometimes shorter and had greater tendency to bend than un-cross-linked actin filaments. Small amounts of cross-linked actin dimers nucleated S1-induced polymerization of actin, but the polymerization by S1 was inhibited for pure populations of cross-linked dimers, trimers, and oligomers. The cross-linked dimers did not decrease the kinetic difference between the polymerization of actin by S1 isozymes S1(A1) and S1(A2). According to electron microscopy evidence, cross-linked actin oligomers polymerized by S1 yielded much shorter arrowhead structures than the un-cross-linked actin. These results indicate the importance of lateral actin-actin interaction for the activation of myosin ATPase and the polymerization of actin by S1.
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PMID:Intrastrand cross-linked actin between Gln-41 and Cys-374. II. Properties of cross-linked oligomers. 992 45

Magnesium (Mg2+) is the physiological divalent cation stabilizing nucleotide or nucleotide analog in the active site of myosin subfragment 1 (S1). In the presence of fluoride, Mg2+ and MgADP form a complex that traps the active site of S1 and inhibits myosin ATPase. The ATPase inactivation rate of the magnesium trapped S1 is comparable but smaller than the other known gamma-phosphate analogs at 1.2 M-1 s-1 with 1 mM MgCl2. The observed molar ratio of Mg/S1 in this complex of 1.58 suggests that magnesium occupies the gamma-phosphate position in the ATP binding site of S1 (S1-MgADP-MgFx). The stability of S1-MgADP-MgFx at 4 degrees C was studied by EDTA chase experiments but decomposition was not observed. However, removal of excess fluoride causes full recovery of the K+-EDTA ATPase activity indicating that free fluoride is necessary for maintaining a stable trap and suggesting that the magnesium fluoride complex is bonded to the bridging oxygen of beta-phosphate more loosely than the other known phosphate analogs. The structure of S1 in S1-MgADP-MgFx was studied with near ultraviolet circular dichroism, total tryptophan fluorescence, and tryptophan residue 510 quenching measurements. These data suggest that S1-MgADP-MgFx resembles the M**.ADP.Pi steady-state intermediate of myosin ATPase. Gallium fluoride was found to compete with MgFx for the gamma-phosphate site in S1-MgADP-MgFx. The ionic radius and coordination geometry of magnesium, gallium and other known gamma-phosphate analogs were compared and identified as important in determining which myosin ATPase intermediate the analog mimics.
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PMID:Inhibition of myosin ATPase by metal fluoride complexes. 1008 41

Here we describe the in vitro polymerization of actin from maize (Zea mays) pollen. The purified actin from maize pollen reported in our previous paper (X. Liu, L.F. Yen [1992] Plant Physiol 99: 1151-1155) is biologically active. In the presence of ATP, KCl, and MgCl2 the purified pollen actin polymerized into filaments. During polymerization the spectra of absorbance at 232 nm increased gradually. Polymerization of pollen actin was evidently accompanied by an increase in viscosity of the pollen actin solution. Also, the specific viscosity of pollen F-actin increased in a concentration-dependent manner. The ultraviolet difference spectrum of pollen actin is very similar to that of rabbit muscle actin. The activity of myosin ATPase from rabbit muscle was activated 7-fold by the polymerized pollen actin (F-actin). The actin filaments were visualized under the electron microscope as doubly wound strands of 7 nm diameter. If cytochalasin B was added before staining, no actin filaments were observed. When actin filaments were treated with rabbit heavy meromyosin, the actin filaments were decorated with an arrowhead structure. These results imply that there is much similarity between pollen and muscle actin.
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PMID:Polymerization of Actin from Maize Pollen. 1222 43

Objective. To study the influence of Ca2+ and Mg2+ on the enzymatic properties of cardiac muscle myosin. Method. A convenient method for the purification myosin from the left ventricle of rabbit heart was described. The Km and Vmax of Ca(2+)-activated and Mg(2+)-activated ATPase and the effects on the enzymatic properties of myosin ATPase in different ionic concentration and different pH range were determined from the rate of Pi release in enzymatic reaction. Result. The Km values of Ca2+, Mg(2+)-activated myosin ATPase at high ionic [correction of ironic] strength were 5.27 +/- 2.10 mmol, 7.04 +/- 2.06 mmol and the Vmax values were 1.10 +/- 0.13 micromoles mg-1 min-1, 0.617 +/- 0.09 micromoles mg-1 min-1 respectively. The Km of Ca(2+)-activated ATPase was higher than that of Mg(2+)-activated ATPase. But the ATPase activity of Ca2+ was influenced by the concentrations of MgCl2. The effect of Ca(2+)-activated ATPase increase was found at lower MgCl2 concentrations. As the MgCl2 concentration increased above 6 mmol/L, Ca2+ sensitivity was decreased. The pH-activity profiles showed that Mg(2+)-activated myosin ATPase activity was more stable than that of Ca(2+)-activated. Conclusion. The mechanism of Ca2+ and Mg2+ effect on myosin ATPase were different. Mg2+ is essential to maintain the conformation of enzymatic activity of myosin in cardiac muscle contraction. Ca2+ is likely acted as a role conducting signals and regulating function.
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PMID:[Effects of Ca2+ and Mg2+ on the enzymatic properties of cardiac muscle myosin]. 1244 42


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