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 present understanding of the relationship between the structure of the myosin ATPase and its role in force production for muscle contraction is reviewed. Emphasis is placed on structural transitions in myosin that occur during ATP hydrolysis which may be correlated with force production. Although detailed structural information is presently lacking, numerous spectroscopic and kinetic experiments have indicated that myosin exists in two structural states for each chemical intermediate in the hydrolysis of ATP. Models are discussed which view a transition between these two states as the energy transduction "event" (i.e., force production).
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PMID:The structure of myosin and its role in energy transduction in muscle. 294 Oct 36

We measured the interrelationships between ventricular muscle myosin mass, myosin ATPase activity and collagen in cats with varying degrees of hypertrophy from left ventricular (LV) pressure-overload produced by either aortic banding or renal hypertension. In order to compare two models of LV pressure-overload with different time courses of progression, the results were analyzed as a function of LV mass or LV weight/body weight (LV/BW) ratio. Myosin was quantitated by SDS-polyacrylamide gel electrophoresis and hydroxyproline was measured as an index of collagen. Myosin concentration was positively correlated with increasing LV mass in control cats. However, in pressure-overloaded LV, myosin concentration was elevated and nearly constant for LV less than 9.0 g, but decreased in LV greater than 9.0 g. Myosin concentration in pressure-overloaded LV was greatest before a significant increase in LV/BW ratio. Hydroxyproline concentration was inversely related to myosin concentration in both LV pressure-overload models and increased with the severity of hypertrophy. Actomyosin ATPase activity in pressure-overloaded LV, was not significantly different from control over a wide range of LV/BW ratios. However, absolute myosin ATP hydrolysis in pressure-overloaded LV, increased by as much as 40%, relative to control, due primarily to increased myosin. The changing spectrum and interrelationships of myosin and collagen were independent of the mechanism of pressure-overload, but were correlated with the severity of hypertrophy.
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PMID:Myocardial changes during the progression of left ventricular pressure-overload by renal hypertension or aortic constriction: myosin, myosin ATPase and collagen. 295 26

In our model of regulation, the observed lack of cooperativity in the binding of myosin subfragment 1 (S-1) with bound ATP to the troponin-tropomyosin-actin complex (regulated actin) is explained by S-1.ATP having about the same affinity for the conformation of the regulated actin that activates the myosin ATPase activity (turned-on form) and the conformation that does not activate the myosin ATPase activity (turned-off form). This predicts that, in the absence of Ca2+, S-1.ATP should not turn on the regulated actin filament. In the present study, we tested this prediction by using either unmodified S-1 or S-1 chemically modified with N,N'-p-phenylenedimaleimide (pPDM X S-1) so that functionally it acts like S-1.ATP, although it does not hydrolyze ATP. We found that, in the absence of Ca2+, neither S-1.ATP nor pPDM X S-1.ATP significantly turns on the ATPase activity of the regulated complex of actin and S-1 (acto X S-1). In contrast, in the presence of Ca2+, pPDM X S-1.ATP binding almost completely turns on the regulated acto.S-1 ATPase activity. These results can be explained by our original cooperativity model, with pPDM X S-1.ATP binding only approximately equal to 2-fold more strongly to the turned-on form than to the turned-off form of regulated actin. However, our results are not consistent with our alternative model, which predicts that if pPDM X S-1.ATP binds to actin in the absence of Ca2+ but does not turn on the ATPase activity, then it should also not turn on the ATPase activity in the presence of Ca2+.
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PMID:Regulation of actomyosin ATPase activity by troponin-tropomyosin: effect of the binding of the myosin subfragment 1 (S-1).ATP complex. 295 23

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

Effects of K-252a, (8R*, 9S*, 11S*)-(-)-9-hydroxy-9-methoxycarbonyl-8-methyl-2,3,9,10-tetrahydro-8, 11-epoxy-1H,8H,11H-2,7b,11a-triazadibenzo[a,g]cycloocta [cde]trinden-1-one, purified from the culture broth of Nocardiopsis sp., on the activity of myosin light chain kinase were investigated. 1) K-252a (1 x 10(-5) M) affected three characteristic properties of chicken gizzard myosin-B, natural actomyosin, to a similar degree: the Ca2+-dependent activity of ATPase, superprecipitation, and the phosphorylation of the myosin light chain. 2) K-252a inhibited the activities of the purified myosin light chain kinase and a Ca2+-independent form of the enzyme which was constructed by cross-linking of myosin light chain kinase and calmodulin using glutaraldehyde. The degrees of inhibition by 3 x 10(-6) M K-252a were 69 and 48% of the control activities with the purified enzyme and the cross-linked complex, respectively. Chlorpromazine (3 x 10(-4) M), a calmodulin antagonist, inhibited the native enzyme, but not the cross-linked one. These results suggested that K-252a inhibited myosin light chain kinase by direct interaction with the enzyme, whereas chlorpromazine suppressed the enzyme activation by interacting with calmodulin. 3) The inhibition by K-252a of the cross-linked kinase was affected by the concentration of ATP, a phosphate donor. The concentration causing 50% inhibition was two orders magnitude lower in the presence of 100 microM ATP than in the presence of 2 mM ATP. 4) Kinetic analyses using [gama-32P]ATP indicated that the inhibitory mode of K-252a was competitive with respect to ATP (Ki = 20 nM). These results suggest that K-252a interacts at the ATP-binding domain of myosin light chain kinase. The direct action of the compound on the enzyme would explain the multivarious inhibition of myosin ATPase, of superprecipitation, and of the contractile response of smooth muscle.
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PMID:K-252a, a novel microbial product, inhibits smooth muscle myosin light chain kinase. 296 51

A newly developed microtechnique for quantitating activity of myosin ATPase (EC 3.6.1.32) is more sensitive and less time-consuming than existing spectrophotometric methods. Measurement of ATPase activity using the new method can be accomplished in a final volume of 0.25 ml, allowing the assay to be conducted in individual wells of 96-well microplates commonly used for the enzyme-linked immunosorbent assay (ELISA). The microassay is performed by adding purified myosin to microplate wells followed by addition of ATP to initiate the enzymatic reaction. The reaction is subsequently terminated by addition of an acidic solution containing malachite green and ammonium molybdate. The level of inorganic phosphate produced by enzymatic hydrolysis of ATP is measured by scanning the microplates using a microELISA plate reader. An entire 96-well microplate can be scanned in less than 2 min, and data from the microassay can be transferred directly to a microprocessor for statistical analysis. The microassay is capable of detecting between 0.2 and 3 nmol of inorganic phosphate in a reaction volume of 50 microliter, and the ATPase activity of as little as 10 ng of rat cardiac myosin can be measured. The increased sensitivity compared with that of other spectrophotometric assays and ease of performing the microassay enable a detailed analysis of the enzymatic properties of cardiac myosin to be conducted on large numbers of small tissue specimens. Several kinetic properties of rat cardiac myosin were determined using this technique.
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PMID:A microassay for ATPase. 296 57

Biopsies taken from the myocardium of 5 patients with Morbus Fallot and from 1 patient with ventricle septum defect were investigated with a combination of morphometric, biochemical and histophotometric techniques in order to study the cardioprotective effect of cold Kirsch's solution. At the final phase of cardioplegia the cardiomyocytes reveal the following alterations: The volume densities of mitochondria, of their degenerated areas and that of cytoplasmic vacuoles show a significant increase whereas that of myofilaments decreases. Cristae and matrix mitochondriales, however, show only moderate alterations without statistical significance. Biochemically the total ATP-concentration and creatine phosphate (CP)-concentration were more or less diminished, in most of the cases the activity of the myosin ATPase was increased, that of the creatine phosphate kinase (CPK) diminished. Compared with the biochemical estimations of the ATPase activity, its histophotometric estimations yielded corresponding results in 2 of 4 cases. In general our findings confirm the cardioprotective effect of Kirsch's solution. The combination of methods used gives more reliable results than one technique alone.
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PMID:Ultramicroscopic morphometric, biochemical and histophotometric investigations of myocardial biopsies taken from Fallot patients before and after cardioplegia with cold Kirsch's solution. 296 76

In myofilaments obtained by Triton X-100 lysis of frog heart cells in high ionic strength medium, the activity of bound creatine kinase cannot be detected by a coupled enzymatic assay. ATP is channelized toward myosin ATPase, through the unstirred layer near myofilaments and cannot diffuse into the bulk solution. Model systems based upon the coupled kinetics of enzymes co-immobilized on the same surface may explain this behaviour. This may also account for why myofilament-bound creatine kinase is more efficient than free enzyme in the cytosol for the physiological recycling of ADP into ATP.
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PMID:An example of substrate channeling between co-immobilized enzymes. Coupled activity of myosin ATPase and creatine kinase bound to frog heart myofilaments. 297 19

The ATP-induced difference UV-absorption spectrum of myosin isolated from the opaque portion of scallop smooth muscle (opaque myosin) was Ca2+-sensitive at 40 mM KCl and 1.5 M sucrose. On adding sucrose to 1.5 M, the turbidity of myosin decreased to 24% and the characteristic two forms of the difference spectrum, the ATP-form and ADP-form (Morita, F. (1967) J. Biol. Chem. 242, 4501-4506), were distinguishable. In the presence of Ca2+, the difference spectrum was the ATP-form first and then decayed into the ADP-form with the depletion of ATP. In the absence of Ca2+, however, only the ADP-form was observed. The ADP-form observed in the absence of Ca2+ returned to the ATP-form when the regulatory light chain-a (RLC-a), one of the regulatory light chains of opaque myosin, was phosphorylated. These results suggest that the main intermediate at the steady state of opaque myosin ATPase is converted depending on the concentration of Ca2+, from EPADP in the presence of Ca2+ to EADP in the absence of Ca2+. It changes to EPADP in the absence of Ca2+ on the phosphorylation of RLC-a. Consistent results were obtained by measuring the ATP-induced Trp-fluorescence increase of opaque myosin in the absence of sucrose. Since the opaque portion of scallop smooth muscle is known to be responsible for catch contraction (Ruegg, J.C. (1961) Proc. R. Soc. London Ser. B 154, 224-249), these findings lead us to suppose that the opaque myosin in vivo may stay in the E.ADP complex during the catch state. It changes to EPADP by the phosphorylation of RLC-a, which may terminate the catch state.
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PMID:The steady state intermediate of scallop smooth muscle myosin ATPase and effect of light chain phosphorylation. A molecular mechanism for catch contraction. 297 52

Regulatory light chain-a myosin kinase (aMK), which phosphorylates one of the myosin regulatory light chains, RLC-a, contained in the catch muscle of scallop, was also found to phosphorylate heavy chains of scallop myosin. After incubation of myosin isolated from the opaque portion of scallop smooth muscle (opaque myosin) with aMK in the presence of [gamma-32P]ATP, about 2 mol of 32P was incorporated per mol of the myosin. The radioactivity was mostly found in the heavy chain at 0.26 M KCl. The pH-activity curve and MgCl2 requirement for the heavy chain phosphorylation were similar to those for RLC-a phosphorylation. In contrast, the dependency of activity on KCl concentration was different from that for RLC-a. The heavy chain phosphorylation activity decreased with increase in KCl concentration up to 0.06 M, and then increased at concentrations over 0.06 M to a maximum at around 0.26 M KCl. This complicated profile probably reflects the solubility of myosin, and the phosphorylation site may be located in the rod portion insoluble at low KCl concentrations. Phosphorylation of heavy chain did not change the solubility of the opaque myosin molecule at all. The acto-opaque myosin ATPase activity in the presence of Ca2+ was found to be decreased to less than one-fourth by the heavy chain phosphorylation.
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PMID:Regulatory light chain-a myosin kinase (aMK) catalyzes phosphorylation of smooth muscle myosin heavy chains of scallop, Patinopecten yessoensis. 297 85


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