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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 was shown that the highly purified monoaldehyde derivative of ADP obtained by partial reduction of the dialdehyde derivative of ADP causes strong irreversible inhibition of the Ca-ATPase activity of myosin subfragment I, the inhibiting effect being of the affinity modification type. The addition to the reaction medium of Mg2+ (but not Ca2+) during the subfragment I interaction with the inhibitor fully prevents the inhibiting effect at all substrates used (Ca-, Mg- or K, EDTA-ATPases). Contrariwise, the subfragment I modified in the absence of Mg2+ exhibits the same degree of inhibition for all the three types of the ATPase activity. An unexpected result that was previously unobserved for other affinity modifiers of myosin ATPase is the maintenance of activity in 50% of active centers, when "two-head" forms of the enzyme (the myosin proper and heavy meromyosin, HMM) are modified. Noteworthy that the affinity modification reaction is characterized by the same values of inhibition constants as in the case of myosin subfragment I (Ki = 3.3-3.5 X 10(-4) M; ki = 0.03-0.04 min-1). This finding provides additional evidence in favour of functional asymmetry of myosin heads in the myosin molecule which seems to be due to the screening of the active center of one head by the other one.
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PMID:[Characteristics of affinity modification of myosin ATPase under the action of monoaldehyde derivatives of ADP]. 183 50

1. The Ca2(+)-activated and Mg2+ actin-activated myosin ATPase activities of flightless mfd- mutant Drosophila flight muscle myosin were one-half and one-third of those of the wild-type fly muscle myosin, respectively. 2. In the two-dimensional gel electrophoresis, the spots corresponding to phosphorylated myosin light chains, Lfl and Ltl, were hardly detected in mfd- mutant myosin. 3. These results support not only the conclusion that phosphorylation of myosin light chains regulates Drosophila myosin ATPase activity but also the assumption that the phosphorylation of myosin light chains is directly involved in flight function of the Drosophila fly.
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PMID:Regulation of Drosophila myosin ATPase activity by phosphorylation of myosin light chains--II. Flightless mfd- fly. 213 98

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

Scallop adductor myosin is regulated by its subunits; the regulatory light chain (R-LC) and essential light chain (E-LC). Myosin light chains suppress muscle activity in the absence of calcium and are responsible for relaxation. The binding of Ca2+ to the myosin triggers contraction by releasing the inhibition imposed on myosin by the light chains. To map the functional domains of the R-LC, we have carried out mutagenesis followed by bacterial expression. Both wild-type and mutant proteins were hybridized to scallop myosin heavy chain/E-LC to map the regions of the light chain that are responsible for the binding to the myosin heavy chain/E-LC, for restoring the specific calcium-binding site, and controlling the myosin ATPase activity. The R-LC is expressed in Escherichia coli using the pKK223-3 (Pharmacia) expression vector and has been purified to greater than 90% purity. E. coli-expressed wild-type R-LC differs from the native R-LC by having the initiating methionine residue and an unblocked NH2 terminus. The wild-type R-LC restores Ca2+ binding and Ca2+ sensitivity when hybridized to scallop myosin. A point mutation of the sixth Ca2(+)-liganding position of domain I (Asp39----Ala39) results in a R-LC that binds more weakly to the heavy chain/E-LC and restores the specific Ca2(+)-binding site but not regulation of the actin-activated Mg2+ ATPase. A second mutation was produced by substituting the last 11 residues of the COOH terminus with 15 different residues. This mutant restores the specific Ca2(+)-binding site, but does not restore Ca2+ regulation to the actin-activated ATPase activity. Several other point mutations do not alter light chain function. The experiments directly establish that the divalent cation-binding site of domain I is functionally distinct from the specific Ca2(+)-binding site. The results indicate that an intact domain I and the COOH terminus are required to suppress the myosin ATPase activity. The fact that the domain I mutation and the COOH-terminal mutation disrupt regulation but do not affect Ca2(+)-binding indicates that these two aspects of regulation are separable and, therefore, the R-LC has distinct functional regions.
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PMID:Regulation of scallop myosin by mutant regulatory light chains. 214 99

Monoclonal antibodies against gizzard smooth muscle myosin were generated and characterized. One of these antibodies, designated MM-2, recognized the 17-kDa light chain and modulated the ATPase activities and hydrodynamic properties of smooth muscle myosin. Rotary shadowing electron microscopy showed that MM-2 binds 51 (+/- 25) A from the head-rod junction. The depression of Ca2+- and Mg2+-ATPase activities of myosin and Ca2+-ATPase activity of heavy meromyosin at low KCl concentration were abolished by MM-2. Viscosity measurement indicated that MM-2 inhibits the transition of 6 S myosin to 10 S myosin. While the rate of the production of subfragment-1 by papain proteolysis of 6 S myosin was inhibited by MM-2, the rate of proteolysis of the heavy chain of 10 S myosin was enhanced by MM-2 and reached the same rate as that of 6 S myosin plus MM-2. These results suggest that MM-2 inhibits the formation of 10 S myosin by binding to the 17-kDa light chain which is localized at the head-neck region of the myosin molecule. MM-2 increased the Vmax of actin-activated Mg2+-ATPase activities of both dephosphorylated myosin and dephosphorylated heavy meromyosin about 10- and 20-fold, respectively. MM-2 also activated the actin-activated Mg2+-ATPase activity of phosphorylated myosin at a low MgCl2 concentration and thus abolished the Mg2+-dependence of acto phosphorylated myosin ATPase activity. These results suggest that MM-2 inhibits the formation of 10 S myosin, and this results in the activation of actin-activated Mg2+-ATPase activity even in the absence of phosphorylation.
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PMID:Inhibition of conformational change in smooth muscle myosin by a monoclonal antibody against the 17-kDa light chain. 246 45

Nuclear histones bind to and precipitate the major contractile proteins, actin and myosin. The binding of histone to actin seems to reach saturation at 2:1 ratio, the interaction may serve some regulatory function(s) in intranuclear events. The binding of histone to myosin is not saturable, and, although it inhibits the actin-activated Mg2+-dependent myosin ATPase activity, does therefore not seem of physiological importance.
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PMID:Histones bind to contractile proteins and inhibit actomyosin ATPase. 252 4

To test the possibility that ATP diffusion limits the kinetics of myosin ATPase (EC. 3.6.1.3) in situ, myosin was covalently bound to the surface of 2 kinds of films: collagen and Immunodyne. On collagen films, it was bound either with 1-ethyl-3 (3 dimethyl-aminopropyl)carbodiimide (EDC) or with dimethyl-3,3'-dithiobis(propionimidate) (DTP). The apparent Km for K+-ATP rose from 0.26 mM for free myosin in solution to 2-5 mM for covalently bound myosin, and maximum K+-ATPase activity was very low. With the other film, Immunodyne from Pall, the maximum activity of bound myosin was 170 nmol per min per 1.5 cm2 film. The apparent Km for K+-ATP was 2.1 mM when the incubation mixture was vigorously stirred, and the effect of stirring indicated that the kinetics of K+-ATP hydrolysis are limited by external diffusion. The large amount of myosin bound per unit of Immunodyne film surface permitted the study of Mg2+-ATPase activity, although it was 400-500 times less than the K+-ATPase activity. The apparently non-Michaelian kinetics of Mg2+-ATP hydrolysis are attributable to the external diffusion. The apparent Michaelis constant observed at low Mg2+-ATP concentrations rose from 0.27 microM for myosin in solution to 5 microM for myosin bound to Immunodyne film.
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PMID:Diffusion-limited kinetics of immobilized myosin ATPase. 252 82

A substance which inhibits the myosin ATPase has been detected from an Okinawan marine sponge. The inhibitor has been isolated from the methanol-soluble extract of the sponge by gel filtration and hydrophobic chromatography. The isolated inhibitor is an amphipathic peptide, which is rich in Asp, Glu, Ser, and Gly, and devoid of Met and Trp. The molecular weight of the peptide is about 6300 as determined by gel filtration, amino acid analysis, and sodium dodecyl sulfate-gel electrophoresis. The peptide is a potent inhibitor not only for the K+-, Ca2+-, and Mg2+-ATPases of myosin, its subfragment-1, and actomyosin, but also for superprecipitation of actomyosin, inhibiting them completely in the range of 10-400 ng/ml. The peptide inhibitor may provide a useful tool to elucidate the structure-function relationship of the myosin ATPase.
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PMID:A novel peptide inhibitor of the myosin ATPase from an Okinawan marine sponge. 253 Feb 20

The heavy chain of myosin from rabbit skeletal muscle can be cleaved at three sites by irradiation with near-ultraviolet light in the presence of 0.1-1.0 mM vanadate. The sigmoidal dependence upon vanadate concentration, with half-maximal rate occurring at about 0.5 mM vanadate and a sigmoidicity of 2.7, is consistent with the chromophore responsible for cleavage being oligomeric vanadate. Cleavage occurs at two sites located within the head region of the molecule, 23 kDa and 75 kDa from the NH2-terminus; these sites are cleaved equally well in heavy meromyosin and subfragment 1. In the presence of 1 mM vanadate, the half-times for cleavage of the 23-kDa and 75-kDa sites are about 15 and 10 min, respectively. The rate of cleavage at both these sites is retarded 2-3-fold by the presence of greater than 10 microM MgATP. The third photocleavage site is located about 5-10 kDa from the COOH terminus of the intact heavy chain, and cleaves equally well in the isolated rod and in light meromyosin. Cleavage at this site occurs with a half-time of 138 min, and its rate is unaffected by the presence of MgATP. The vanadate-mediated cleavage of the heavy chains is accompanied by characteristic changes in the myosin ATPase properties, with the Ca2+, Mg2+ and actin-activated Mg2+ ATPases becoming elevated, whereas the K+/EDTA ATPase becomes inactivated. The sites of photocleavage in the myosin heavy chain might be associated with sites of phosphate binding.
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PMID:Vanadate-mediated photocleavage of rabbit skeletal myosin. 253 8

In order to gain some information regarding Ca2+-dependent ATPase, the enzyme was purified from cardiac sarcolemma and its properties were compared with Ca2+-ATPase activity of myosin purified from rat heart. Both Ca2+-dependent ATPase and myosin ATPase were stimulated by Ca2+ but the maximal activation of Ca2+-dependent ATPase required 4 mM Ca2+ whereas that of myosin ATPase required 10 mM Ca2+. These ATPases were also activated by other divalent cations in the order of Ca2+ greater than Mn2+ greater than Sr2+ greater than Br2+ greater than Mg2+; however, there was a marked difference in the pattern of their activation by these cations. Unlike the myosin ATPase, the ATP hydrolysis by Ca2+-dependent ATPase was not activated by actin. The pH optima of Ca2+-dependent ATPase and myosin ATPase were 9.5 and 6.5 respectively. Na+ markedly inhibited Ca2+-dependent ATPase but had no effect on the myosin ATPase activity. N-ethylmaleimide inhibited Ca2+-dependent ATPase more than myosin ATPase whereas the inhibitory effect of vanadate was more on myosin ATPase than Ca2+-dependent ATPase. Both Ca2+-dependent ATPase and myosin ATPase were stimulated by K-EDTA and NH4-EDTA. When myofibrils were treated with trypsin and passed through columns similar to those used for purifying Ca2+-ATPase from sarcolemma, an enzyme with ATPase activity was obtained. This myofibrillar ATPase was maximally activated at 3-4 mM Ca2+ and 3 to 4 mM ATP like sarcolemmal Ca2+-dependent ATPase. K+ stimulated both ATPase activities in the absence of Ca2+ and inhibited in the presence of Ca2+. Both enzymes were inhibited by Na+, Mg2+, La3+, and azide similarly. However, Ca2+ ATPase from myofibrils showed three peptide bands in SDS polyacrylamide gel electrophoresis whereas Ca2+ ATPase from sarcolemma contained only two bands. Sarcolemmal Ca2+-ATPase had two affinity sites for ATP (0.012 mM and 0.23 mM) while myofibrillar Ca2+-ATPase had only one affinity site (0.34 mM). Myofibrillar Ca2+-ATPase was more sensitive to maleic anhydride and iodoacetamide than sarcolemmal Ca2+-ATPase. These observations suggest that Ca2+-dependent ATPase may be a myosin like protein in the heart sarcolemma and is unlikely to be a tryptic fragment of myosin present in the myofibrils.
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PMID:A comparative study of the rat heart sarcolemmal Ca2+-dependent ATPase and myosin ATPase. 296 55


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