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Query: EC:3.6.3.1 (Mg2+-ATPase)
 1,484 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The actin-activated Mg2+-ATPase activity of dephosphorylated chicken gizzard myosin reconstituted with actin, tropomyosin, myosin light-chain kinase (MLCK) and calmodulin was inhibited completely by purealin, 20 microM, whereas the activity of the phosphorylated and dephosphorylated myosin was not affected. Purealin inhibited the phosphorylation of myosin light chains caused by MLCK and calmodulin (IC50, 5 microM). On the other hand, purealin had no effect on myosin phosphorylation induced by Ca2+ -independent MLCK. The calmodulin-stimulated phosphodiesterase activity was inhibited by purealin (IC50, 7 microM) at concentrations very close to those that inhibit myosin phosphorylation. Kinetic analysis revealed a competitive mode of inhibition of calmodulin-stimulated phosphodiesterase activity by purealin. These results suggest that purealin acts as a calmodulin antagonist in reconstituted actomyosin from chicken gizzard, resulting in inhibition of light chain phosphorylation and the actin-activated ATPase activity of myosin.
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PMID:The mechanism of inhibition of light-chain phosphorylation by purealin in chicken gizzard myosin. 296 81

Highly purified microvillar 110 kDa polypeptide-calmodulin (110K-cam) complex was confirmed to have ATPase activities characteristic of a myosin. The effect of F-actin on these activities was investigated. The Mg2+-ATPase is activated about 2-fold by F-actin in a dose-dependent fashion, whereas the K+-EDTA-ATPase is inhibited by greater than 90% by F-actin. These data provide evidence for a functional relationship between the ATPase activity of 110K-cam and its interaction with F-actin. They also extend the similarities between 110K-cam and myosin. The results suggest that higher cells contain in addition to myosin a second class of myosin-like molecules represented by 110K-cam.
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PMID:ATPase activity of the microvillar 110 kDa polypeptide-calmodulin complex is activated in Mg2+ and inhibited in K+-EDTA by F-actin. 296 14

Acanthamoeba myosin IB contains a 125-kDa heavy chain that has high actin-activated Mg2+-ATPase activity when 1 serine residue is phosphorylated. The heavy chain contains two F-actin-binding sites, one associated with the catalytic site and a second which allows myosin IB to cross-link actin filaments but has no direct effect on catalytic activity. Tryptic digestion of the heavy chain initially produces an NH2-terminal 62-kDa peptide that contains the ATP-binding site and the regulatory phosphorylation site, and a COOH-terminal 68-kDa peptide. F-actin, in the absence of ATP, protects this site and tryptic cleavage then produces an NH2-terminal 80-kDa peptide. Both the 62- and the 80-kDa peptides retain the (NH+4,EDTA)-ATPase activity of native myosin IB and both bind to F-actin in an ATP-sensitive manner. However, only the 80-kDa peptide retains a major portion of the actin-activated Mg2+-ATPase activity. This activity requires phosphorylation of the 80-kDa peptide by myosin I heavy chain kinase but, in contrast to the activity of intact myosin IB, it has a simple, hyperbolic dependence on the concentration of F-actin. Also unlike myosin IB, the 80-kDa peptide cannot cross-link F-actin filaments indicating the presence of only a single actin-binding site. These results allow the assignment of the actin-binding site involved in catalytic activity to the region near, and possibly on both sides of, the tryptic cleavage site 62 kDa from the NH2 terminus, and the second actin-binding site to the COOH-terminal 45-kDa domain. Thus, the NH2-terminal 80 kDa of the myosin IB heavy chain is functionally similar to the 93-kDa subfragment 1 of muscle myosin and most likely has a similar organization of functional domains.
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PMID:Localization of the actin-binding sites of Acanthamoeba myosin IB and effect of limited proteolysis on its actin-activated Mg2+-ATPase activity. 296 46

Smooth muscle myosin can be phosphorylated by myosin light chain kinase at the serine 19 and threonine 18 residues of the two 20,000-dalton light chains (Ikebe, M., Hartshorne, D. J., and Elizinga, M. (1986) J. Biol. Chem. 261, 36-39). These studies with myosin and heavy meromyosin (HMM) compare the effects induced by phosphorylation of serine 19 (M2P and HMM2P) and serine 19 plus threonine 18 (M4P and HMM4P). Formation of M4P altered the KCl dependence of viscosity and Mg2+-ATPase and higher values were maintained at lower ionic strengths, compared to M2P or dephosphorylated myosin (Mo). This is consistent with the stabilization of the 6 S conformation. The tendency for aggregation, as judged by light scattering, followed the sequence M4P greater than M2P greater than Mo. Filaments formed with M4P were more resistant to dissociation by ATP compared to filaments of M2P. Phosphorylation of HMM2P doubled Vmax of actin-activated ATPase with little effect on the apparent affinity for actin. The Mg2+-ATPase of HMM4P exhibited a higher activity at low ionic strength compared to HMM2P and HMMo. Hydrodynamic differences were detected at low ionic strength in the presence of ATP by sedimentation velocity measurements with HMM4P, HMM2P, and HMMo. Proteolysis by papain indicated an increased susceptibility of the head-neck junction of HMM4P compared to HMM2P. These data suggest that the phosphorylation of threonine 18 in addition to serine 19 change the conformation of myosin and HMM and this is associated with altered biological properties.
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PMID:Effects of phosphorylation of light chain residues threonine 18 and serine 19 on the properties and conformation of smooth muscle myosin. 296 56

Purified bovine brain myosin contained approximately 1 and 3 mol of protein-bound phosphate/mol myosin in the light chains and heavy chains, respectively. Large portions of this light chain- and heavy chain-bound phosphate (about 0.8 and 2.4 mol, respectively) were removed by incubation with a brain phosphoprotein phosphatase and potato acid phosphatase, respectively. Upon phosphorylation of the dephosphorylated brain myosin with myosin light chain kinase and casein kinase II, about 1.6 and 3.0 mol of phosphate was incorporated into the light chains and heavy chains, respectively, while much lower levels of phosphate were incorporated into the non-dephosphorylated brain myosin under the same conditions. The actin-activated Mg2+-ATPase activity of brain myosin rephosphorylated with myosin light chain kinase was about twice as high as that of dephosphorylated brain myosin (about 30 and 15 nmol phosphate/mg/min, respectively). On the other hand, whereas the rephosphorylated brain myosin superprecipitated rapidly with F-actin, the rate of superprecipitation of the dephosphorylated brain myosin was extremely low. Under appropriate conditions, a loose network of tiny superprecipitates, which formed initially throughout the solution, contracted to form eventually a large and dense particle. These results indicate that phosphorylation of the light chains of brain myosin is a prerequisite for the contraction of brain actomyosin. The role of phosphorylation of the heavy chains by casein kinase II remains to be elucidated.
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PMID:The effects of phosphorylation and dephosphorylation of brain myosin on its actin-activated Mg2+-ATPase and contractile activities. 296 85

Polyclonal antibodies raised against a synthetic peptide consisting of the last 19 amino acids at the end of the coiled-coil region of the heavy chains inhibited the actin-activated Mg2+-ATPase activity of myosin II and its ability to form filaments. Antibodies against a synthetic peptide corresponding to the 21 adjacent amino acids at the beginning of the non-helical tailpiece, which include the three regulatory phosphorylatable serines, had no effect on either activity.
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PMID:Enzymatic activity and filament assembly of Acanthamoeba myosin II are regulated by adjacent domains at the end of the tail. 296 22

To investigate the possibility of cooperative interactions between the two myosin heads in muscle contraction, Ca2+-activated force development, K+-EDTA- and Mg2+-ATPase activities, muscle fiber stiffness, and the velocity of unloaded shortening were measured on partially p-PDM treated glycerinated muscle fibers, which contained a mixture of myosin molecules with zero, one and two of their heads inactivated. It was found that the magnitude of the Ca2+-activated isometric force development was proportional to the square of both K+-EDTA- and Mg2+-ATPase activities and also to the square of muscle fiber stiffness. If the two myosin heads in the glycerinated fibers are assumed to react independently with p-PDM, the above results strongly suggest that (i) each myosin molecule in the thick filaments can generate force only when its two heads do not react with p-PDM, (ii) muscle fiber stiffness is determined by the total number of native heads, and (iii) there is no cooperative interaction between the two myosin heads in catalyzing ATP hydrolysis.
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PMID:Cooperative interactions of myosin two heads in muscle force generation. 297 Feb 9

The actin-activated Mg2+-ATPase activity of smooth muscle myosin was measured in 85 mM KCl, 6 mM MgCl2 in the absence of tropomyosin. The activity was dependent on myosin concentration. Vmax increased as myosin concentration was increased, while the Ka (the apparent dissociation constant for actin) remained the same. The extent of filament formation was also correlated with myosin concentration and most of the myosin monomers existed in 10S conformation. These results suggest that myosin concentration influences the actin-activated Mg2+-ATPase activity by changing the 10S-6S-filaments equilibrium.
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PMID:Increase in the actin-activated Mg2+-ATPase activity of smooth muscle myosin by increasing myosin concentration. 297 Feb 61

Isoelectric focusing of purified vascular smooth muscle myosin revealed two variants of the 17,000-dalton light chain subunits. The isoelectric points of the light chain variants were determined to be 4.13 (LC17a) and 4.19 (LC17b). Tryptic peptide maps of the two species of light chain generated by reverse-phase high performance liquid chromatography disclosed small but obvious differences in peptide composition while amino acid analyses of the variants were quite similar. Two-dimensional electrophoresis of extracts from various mammalian smooth muscles revealed tissue-specific differences in the relative content of LC17a and LC17b. Vascular (aorta, carotid, and pulmonary artery) muscles and tracheal smooth muscle contained both light chain variants while smooth muscle of the gastrointestinal tract (stomach and jejunum) contained LC17a only. The actin-activated Mg2+-ATPase activities of both phosphorylated and nonphosphorylated stomach (LC17b = 0) and aortic (LC17b = 40%) myosins were compared. In the presence of saturating tropomyosin, a 2-fold difference in Vmax was measured: phosphorylated, aortic, 0.119 +/- 0.009 versus stomach, 0.239 +/- 0.012 mumol of PO4 liberated/min/mg of myosin; nonphosphorylated, aortic, 0.065 +/- 0.004 versus stomach, 0.123 +/- 0.004 mumol of PO4 liberated/min/mg of myosin. In addition, the Vmax of myosin subfragment-1 ATPase from bovine aortic, pulmonary artery, and stomach myosins (LC17b contents, 40, 20, and 0%, respectively) was found to decrease in direct proportion to the LC17b content. Our results suggest that isoforms of the 17,000-dalton light chain subunits of mammalian smooth muscle myosin could play an important role in modulating actomyosin ATPase activity.
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PMID:Distribution of isoelectric variants of the 17,000-dalton myosin light chain in mammalian smooth muscle. 297 67

A study was made of changes in F-actin conformation occurring in a myosin-free single ghost fibre induced by the binding of glycolytic enzyme lactate dehydrogenase (LDG) to F-actin. The formation of the complex between LDG and F-actin induces changes in the parameters of the intrinsic (tryptophan) and extrinsic (rodominil--phalloin) polarized fluorescence of F-actin of the ghost muscle fibre. It is found that LDG stimulates Mg2+-ATPase of actomyosin in solution. It is assumed that the coupling of energy-providing mechanism with that of muscle contraction may be accomplished through the conformation changes in F-actin.
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PMID:[Interaction of the enzymes of cellular energy support with the F-actin of the thin filaments of muscle fiber. I. The binding of lactate dehydrogenase with F-actin induces changes in the structural state of the components of the complex]. 297 67


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