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)

A study of the K+-activated myosin ATPase activity, which was measured at high ionic strength in the absence of divalent cations, permitted estimates of the actin-myosin interaction under conditions where (i) myosin-myosin interactions were prevented, (ii) the actin-myosin interaction could be studied in the presence of ATP, and (iii) variation in myosin light chain phosphorylation did not alter smooth muscle myosin ATPase activity. A comparison of myosins isolated from swine carotid arteries and mixed (leg and back) rabbit skeletal muscle was conducted in the presence and absence of rabbit skeletal actin. It was found that (i) arterial myosin, like skeletal myosin, exhibited hyperbolic kinetics for ATP hydrolysis, (ii) specific ATPase activities were significantly higher for skeletal myosin, (iii) saturating concentrations of actin appear to totally inhibit the arterial myosin ATPase activity, but only partially inhibit skeletal myosin activity, (iv) the free actin concentration required for half-maximal inhibition was significantly lower for the arterial myosin ATPase activity than for the skeletal myosin activity; (v) unlike skeletal actomyosin, arterial actomyosin exhibits tight binding characteristics in the presence of ATP, (vi) the binding stoichiometry for arterial myosin to skeletal F-actin was 2 mol of actin monomer/mol of myosin. These observations reveal differences in the interaction of arterial and skeletal myosin with actin, and may in part, explain the high force-generating characteristics of arterial smooth muscle.
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PMID:Tight binding of arterial myosin to skeletal F-actin. 644 57

Actomyosin isolated from bovine stomach muscle contains the endogenous light-chain kinase and phosphatase. Myosin can be separated from other proteins by gel filtration on a Sepharose 4B--agarose column. The amount of phosphate covalently bound to the 20 000-dalton light chains of purified myosin can be controlled by phosphorylation or dephosphorylation using the endogenous enzymes prior to column purification. The purified myosin can serve as a substrate for exogenously added light-chain kinase and phosphatase, but the myosin itself is free of the activities for both enzymes. The adenosine 5'-triphosphatase (ATPase) activity of myosin was activated by rabbit skeletal muscle actin only when the 20 000-dalton light chain was phosphorylated. The level of activation correlated with the amount of phosphate bound to the light chain. The maximum activation by pure actin was observed when the molar ratio of myosin to actin was 1:20. The activation was dependent on the amount of phosphate bound to the myosin light chain at all levels of actin concentrations. The actin-activated ATPase activity of stomach muscle myosin is not dependent on Ca2+ concentration once the myosin is phosphorylated and is free of kinase and phosphatase activity. The actin-activated ATPase activity was higher when the actin was complexed with tropomyosin. The highest level of activation was obtained when the myosin was fully phosphorylated and the actin was complexed with tropomyosin at a molar ratio of 1:6 (Tm/A). The potentiation of actin-activated ATP hydrolysis by tropomyosin is not dependent on Ca2+. These data indicate that tropomyosin plays a major role in the actin-activated ATP hydrolysis by smooth muscle myosin in the absence of other regulatory proteins.
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PMID:Effects of phosphorylation, calcium ion, and tropomyosin on actin-activated adenosine 5'-triphosphatase activity of mammalian smooth muscle myosin. 645 59

Specific antibodies directed against the regulatory light chains (R-LC) or essential light chains (SH-LC) of scallop myosin abolished calcium regulation in myofibrils, myosin, and heavy meromyosin by elevating the actin-activated Mg2+-ATPase activity in the absence of calcium. Calcium dependence was completely eliminated at molar ratios of 2.5-3 antibodies bound per myosin. Monovalent anti-R-LC Fab and anti-SH-LC Fab fragments also desensitized myofibrils fully. High Ca2+-ATPase activity remained unaffected by the antibodies. Anti-SH-LC IgG reduced to about one-half the actin-activated Mg2+-ATPase in the presence of calcium and the potassium-activated ethylenediaminetetraacetic acid (EDTA)-ATPase activities. Anti-SH-LC Fab, however, desensitized without inhibiting the actin-activated Mg2+-ATPase. The desensitizing effect of both antibodies was abolished by prior absorption with the homologous myosin light chain. Calcium binding and R-LC and anti-SH-LC IgG's and by anti-SH-LC Fab. The anti-R-LC Fab fragment induced a significant (70%) dissociation of R-LC from myofibrils and myosins with concomitant losses in calcium binding. In contrast, anti-R-LC IgG prevented the dissociation of R-LC from myosin by EDTA. Binding of anti-R-LC IgG to myofibrils was proportional to thier R-LC content. Increased amounts of anti-SH-LC IgG were bound by myofibrils devoid of R-LC. Bound anti-SH-LC antibody significantly inhibited the reuptake of R-LC by EDTA-treated myofibrils as well as the full binding of anti-R-LC antibody. Certain rabbits produced a population of anti-SH-LC antibodies which were specific for this light chain and bound extensively to myosin but failed to desensitize it (nondesensitizing anti-SH-LC antibody). The desensitizing and nondesensitizing anti-SH-LC populations bound to different regions of the SH-LC on the myosin, and the binding of the two types of antibody to the SH-LC was nearly additive. The nondesensitizing SH-antibody inhibited the reuptake of R-LC less, and its binding to myofibrils was not influenced by the absence of R-LC. These studies indicate a direct or indirect involvement of the SH-LC's in myosin-linked regulation, raise the possibility of an interaction between the R-LC and SH-LC, and confirm the regulatory function of the scallop R-LC. A model for a relative location of the two types of light chains and the involvement of the subfragment-2 region of myosin linked regulation is discussed.
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PMID:An immunological approach to myosin light-chain function in thick filament linked regulation. 2. Effects of anti-scallop myosin light-chain antibodies. Possible regulatory role for the essential light chain. 645 95

In this study, myosin types in human skeletal muscle fibers were investigated with electrophoretic techniques. Single fibers were dissected out of lyophilized surgical biopsies and typed by staining for myofibrillar ATPase after preincubation in acid or alkaline buffers. After 14C-labelling of the fiber proteins in vitro by reductive methylation, the myosin light chain pattern was analysed on two-dimensional gels and the myosin heavy chains were investigated by one-dimensional peptide mapping. Surprisingly, human type I fibers, which contained only the slow heavy chain, were found to contain variable amounts of fast myosin light chains in addition to the two slow light chains LC1s and LC2s. The majority of the type I fibers in normal human muscle showed the pattern LC1s, LC2s and LC1f. Further evidence for the existence in human muscle of a hybrid myosin composed of a slow heavy chain with fast and slow light chains comes from the analysis of purified human myosin in the native state by pyrophosphate gel electrophoresis. With this method, a single band corresponding to slow myosin was obtained; this slow myosin had the light chain composition LC1s, LC2s and LC1f. Type IIA and IIB fibers, on the other hand, revealed identical light chain patterns consisting of only the fast light chains LC1f, LC2f and LC3f but were found to have different myosin havy chains. On the basis of the results presented, we suggest that the histochemical ATPase normally used for fibre typing is determined by the myosin heavy chain type (and not by the light chains). Thus, in normal human muscle a number of 'hybrid' myosins were found to occur, namely two extreme forms of fast myosins which have the same light chains but different heavy chains (IIA and IIB) and a continuum of slow forms consisting of the same heavy chain and slow light chains with a variable fast light chain composition. This is consistent with the different physiological roles these fibers are thought to have in muscle contraction.
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PMID:Analysis of myosin light and heavy chain types in single human skeletal muscle fibers. 645 76

The relationship between the actin-activated adenosinetriphosphatase activity of smooth muscle myosin and the extent of myosin light chain phosphorylation is nonlinear. It is suggested that the phosphorylation of the two heads of smooth muscle myosin is an ordered process and that the two heads are influenced by cooperative interactions.
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PMID:Phosphorylation of smooth muscle myosin: evidence for cooperativity between the myosin heads. 645 37

This paper reports the following data with regard to the BBWT cardiovascular system: 1) Arterial Blood pressure progressively increases from 1 to 12 month of age, accompanied by marked left ventricular hypertrophy; 2) The myosin ATPase activity is enhanced about three times; 3) No differences in myosin light chain pattern is observed; 4) The peptide pattern obtained after chymotryptic digestion of the myosin molecule shows that some peptides, which are not evident or barely discernible, in 1 month old animal, are present in the adult one. These findings are surprising because it is well known that the ATPase activity decreases with age and hypertrophy. It is possible that other factors, as the levels of circulating cathecolamines or the thyroid hormones, are involved in the control of myosin synthesis and consequently in its ATPase activity.
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PMID:Changes in ventricular myosin properties during broad breasted white turkey (BBWT) development. 645 20

Perfusion of isolated rat hearts with isoproterenol resulted in increases in the level of protein-bound phosphate of the myofibrils. After perfusion of the hearts with 32P, followed by SDS-polyacrylamide gel electrophoresis of the purified myofibrils, four major 32P-containing protein bands were identified. Most of the increased 32P incorporation produced by isoproterenol was localized on the troponin I and myosin light chain bands, and, to lesser extent, on the M-protein band. ATPase activity was tested in the purified myofibrils. No changes in Ca2+ requirement for activation were found after isoproterenol perfusion. However, maximal ATPase activity was markedly reduced in the myofibrils obtained from isoproterenol-treated hearts. It would appear that the myofibrillar protein phosphorylation induced by isoproterenol perfusion results in a decrease in actomyosin ATPase activity.
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PMID:Effects of isoproterenol treatment of isolated perfused rat hearts on myofibrillar phosphorylation and ATPase activity. 646 Jul 94

Thyroidal trophic effects on slow-twitch skeletal muscle properties were compared in normally innervated and denervated soleus of rats maintained at different thyroid states. Hypothyroidism caused fast to slow changes in fiber type composition (99% decrease in proportion of type II fibers), ATPase activities (down 20-30%), myosin light chain pattern (54% less fast light chains), calcium uptake by SR (down 60%), LDH activity (down 11%), and isozyme pattern (9% decrease in M-subunits). Changes of similar magnitude but opposite in direction were induced by thyrotoxicosis. Denervations reversed, to varying degrees, the fast to slow transformations observed in hypothyroidism. However the slow to fast changes found in hyperthyroidism were facilitated rather than inhibited by denervation. These latter results clearly show that the hormone effect can be elicited in the absence of motor innervation. Furthermore, denervation alone caused slow to fast changes in euthyroid muscles. From these results, it is proposed that denervation and dysthyreosis alter muscle properties by independent mechanisms. Our data favor a direct action of thyroid hormone over a neurally mediated mechanism.
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PMID:Evidence for a direct action of thyroid hormone in specifying muscle properties. 646 Dec 59

Ca2+ binding to myofibrillar regulatory sites can produce conformational changes allowing cross-bridge attachment and cycling. Measurements of smooth muscle actomyosin ATPase activity suggested that Ca2+ might act indirectly to mediate cross-bridge attachment by stimulating myosin light chain phosphorylation. However, the predicted obligatory relationship between developed force and myosin phosphorylation was not always observed in living smooth muscle. The observation that myosin phosphorylation was always tightly correlated with average cross-bridge cycling rates estimated from isotonic shortening velocities suggested that Ca2+ has two regulatory roles. One action is exerted via a Ca2+-binding protein whose identity is unknown in smooth muscle. This regulatory site acts like other Ca2+-binding regulatory proteins in muscle to permit cross-bridge interaction and to determine active stress. The second regulatory role involves stimulation of myosin light chain kinase and light chain phosphorylation. Increasing the level of phosphorylated cross-bridges increases shortening velocities or rate of force development. We suggest that the dephosphorylated cross-bridges are noncycling or slowly cycling in activated smooth muscle. Smooth muscle may be a particularly favorable experimental preparation for demonstrating a general regulatory role of myosin phosphorylation in modulating the kinetics and energetics of muscle contraction.
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PMID:The role of myosin light chain phosphorylation in regulation of the cross-bridge cycle. 684 78

The rate of splitting of energy-rich phosphate compounds and the extent of myosin light chain phosphorylation in contracting mouse extensor digitorum longus (EDL, fast twitch) and soleus (slow twitch) muscles were studied at 20 degrees C. The rate of high energy phosphate-splitting during a maintained isometric tetanus was 1.44 +/- 0.21 mumol . g-1 . s-1 in soleus. In EDL, the splitting rate was higher, 3.71 +/- 0.62 mumol . g-1 . s-1, during the first several seconds and thereafter was reduced to a rate of 1.63 +/- 0.35 mumol . g-1 . s-1 between 12 and 15 s of stimulation. Light chains identified on 2-dimensional gel electrophoretograms from EDL corresponded to the light chain composition of fast twitch muscle (LC1f, LC2f, and LC3f). Soleus is composed of fast twitch and slow twitch fibers because 2 additional light chains were found: LC1s and LC2s. In unstimulated EDL and soleus muscles, 0.1 of the LC1f and LC2s were phosphorylated. Upon stimulation, only LC2f, and only in EDL, increased its extent of phosphorylation. The time course of increase in phosphorylation of LC2f and decrease in rate of high energy phosphate-splitting correspond so that the 2 processes may be mechanistically related. If so, it appears that myosin LC2f phosphorylation represents a thick filament regulatory system capable of downward modulation of actomyosin ATPase in vivo during a maintained contraction.
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PMID:Myosin light chain phosphorylation is associated with a decrease in the energy cost for contraction in fast twitch mouse muscle. 706 10


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