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)

We have reported that the maximal velocity of shortening and myofibrillar adenosine triphosphatase (ATPase) activity of antigen-sensitized airway smooth muscle are higher than that of nonsensitized airway smooth muscle (Kong, S. K., R. P. C. Shiu, and N. L. Stephens. J. Appl. Physiol. 60: 92-94, 1986). To extend these studies, we attempted to determine whether the increased myofibrillar ATPase activity from sensitized airway smooth muscle was associated with either a change in distribution of two myosin heavy chain isozymes or an increase in myosin light chain phosphorylation. Myosin heavy chain isozymes from both control and sensitized airway smooth muscle were separated by 4% sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Gels were analyzed by densitometry, which indicated that isozyme band pattern of sensitized airway smooth muscle was not different from that of the control. The maximal levels of phosphorylated myosin light chain from whole cell homogenates of sensitized and control tracheal smooth muscles were 0.65 +/- 0.029 (n = 6) and 0.40 +/- 0.025 mol Pi/mol light chain (n = 6), respectively. The degree of phosphorylation of myosin light chain of sensitized airway smooth muscle was significantly higher than that of the control (P less than 0.05). This study also indicated that increased myofibrillar ATPase activity in sensitized tracheal smooth muscle was correlated with phosphorylation of myosin light chain.
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PMID:Increased myosin phosphorylation in sensitized canine tracheal smooth muscle. 214 57

The mechanism of the inhibitory effect of caffeine on smooth muscle contraction was examined using chicken gizzard. Caffeine (0.1-5 mmol/l) inhibited the KCl-induced contraction of the muscle with an IC50 of 1.1 mmol/l. Forskolin (0.01-10 mumol/l) also inhibited KCl-induced contraction. The inhibitory effect of caffeine was potentiated by a low concentration of forskolin (0.3 mumol/l) and the inhibitory effect of forskolin was potentiated by a low concentration of caffeine (0.1 mmol/l). Although caffeine and forskolin increased tissue cyclic AMP levels, caffeine inhibited the KCl-induced contraction more strongly than forskolin at a given cyclic AMP level. Caffeine (1-40 mmol/l) inhibited the contractions induced by 3 mumol/l Ca2+ in Triton X-100-permeabilized muscle. Caffeine (1-40 mmol/l) inhibited the phosphorylation of 20 kDa myosin light chain (MLC) in native actomyosin preparation and the inhibition was enhanced by decreasing the ATP concentration in the reaction medium. Calmodulin (CaM) activity, as monitored by Ca2+/CaM-dependent erythrocyte membrane (Ca2+ + Mg2+)-ATPase, was not affected by 20 mmol/l caffeine. Time-dependent dephosphorylation of MLC upon removal of Ca2+, an indicator of phosphate activity, was not affected by caffeine. Caffeine also inhibited the Ca2(+)-independent contraction in thiophosphorylated permeabilized muscle. These results indicate that caffeine inhibits smooth muscle contraction by a direct inhibition of MLC kinase and actin-myosin interaction. A part of the inhibitory effect may be mediated by cyclic AMP-dependent mechanism(s).
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PMID:Direct inhibition of chicken gizzard smooth muscle contractile apparatus by caffeine. 216 Jun 18

The energetics of smooth muscle is characterized by low tension cost (rate of ATP utilization per isometric force/cross-section area), ranging from 100- to 500-fold less than skeletal muscle. The efficiency (ATP usage per work) of smooth muscle, although less well documented, is also somewhat (4-fold) less than skeletal muscle. Another well-known characteristic of smooth muscle is the linear relation between the steady-state of ATP utilization (JATP) and isometric force. Recently, Murphy and colleagues [C.-M. Hai and R. A. Murphy. Am. J. Physiol. 254 (Cell Physiol. 23) C99-C106, 1988] have put forth a kinetic model of cross-bridge regulation that predicts the time course of stress and myosin light chain phosphorylation (MLC-Pi). The energetics consequences of this model, in brief, are that the low tension cost is partly attributed to a slow detachment rate of the myosin cross bridge when dephosphorylated when attached to actin ("latch state"), whereas the lower efficiency is ascribed to a high rate of myosin phosphorylation-dephosphorylation inherent to a fit of data to this kinetic scheme. This latter corollary is somewhat controversial in light of current interpretations of smooth muscle energetics data. Using SCoP software (National Biomedical Simulation Resource, Duke University), we tested this model in terms of fitting existing data with respect to 1) is a high myosin-dephosphorylation adenosine triphosphatase (ATPase) necessary to fit the available data on the time course of stress and MLC-Pi?; and 2) can this model predict the observed linear relation between the steady-state rate of ATP hydrolysis (JATP) and isometric force?(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Smooth muscle energetics and theories of cross-bridge regulation. 230 74

KT5926, (8R*,9S*,11S*)-(-)-9-hydroxy-9-methoxycarbonyl-8-methyl-14-n-propoxy-2,3 ,9, 10-tetrahydro-8,11-epoxy, 1H,8H, 11H-2,7b,11a-triazadibenzo[a,g]cycloocta[cde] trinden-1-one, was found to be a potent and selective inhibitor of myosin light chain kinase. The compound inhibited both Ca2+/calmodulin-dependent and -independent smooth muscle myosin light chain kinases to a similar extent. The inhibition was not affected by the concentration of calmodulin. Kinetic analyses showed that the mode of inhibition was of the competitive type with respect to ATP (Ki, 18 nM) and of the noncompetitive type with respect to myosin light chain (Ki, 12 nM). These results indicated that KT5926 directly interacted with the enzyme at the catalytic site. KT5926 also inhibited other protein kinases, but with relatively high Ki values; the values for protein kinase C, cAMP-dependent protein kinase, and cGMP-dependent protein kinase were 723, 1200, and 158 nM, respectively. Ca2(+)-ATPase, Na+/K(+)-ATPase, hexokinase, and 5'-nucleotidase were not inhibited by KT5926 at less than 10 microM. The effect of KT5926 on serotonin secretion and protein phosphorylation induced by platelet-activating factor or phorbol ester was examined in rabbit platelets. KT5926 inhibited the phosphorylation of a 20-kDa protein but had no effect on the phosphorylation of a 40-kDa protein, thereby indicating that the compound exerts its selective inhibition of myosin light chain kinase in intact cells. The compound inhibited serotonin secretion induced by platelet-activating factor, but its potency was significantly less than that 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, which inhibited the phosphorylation of both the 20-kDa protein and the 40-kDa protein. Phorbol ester-induced secretion was not suppressed by KT5926. These results provide the evidence that both the 20-kDa protein phosphorylation by myosin light chain kinase and the 40-kDa protein phosphorylation by protein kinase C substantially contribute to the secretion response in platelets.
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PMID:KT5926, a potent and selective inhibitor of myosin light chain kinase. 232 35

Bovine platelet myosin is phosphorylated by protein kinase C at multiple sites. Most of the phosphate is incorporated in the 20,000-dalton light chain although some phosphate is incorporated in the heavy chain. Phosphorylation of the 20,000-dalton light chain of platelet myosin is 10 times faster than the phosphorylation of smooth muscle myosin. Platelet myosin light chain is first phosphorylated at a threonine residue followed by a serine residue. Dominant phosphorylation sites of the 20,000-dalton light chain are estimated as serine-1, serine-2, and threonine-9. Prolonged phosphorylation by protein kinase C resulted in an additional phosphorylation site which, on the basis of limited proteolysis, appears to be either serine-19 or threonine-18. Phosphorylation by protein kinase C causes an inhibition of actin-activated ATPase activity of platelet myosin prephosphorylated by myosin light chain kinase. Inhibition of ATPase activity is due to a decreased affinity of myosin for actin, and no change in Vmax is observed. It is shown that platelet myosin also exhibits the 6S to 10S conformation transition as judged by viscosity and gel filtration methods. Mg2(+)-ATPase activity of platelet myosin is paralleled with the 10S-6S transition. Phosphorylation by protein kinase C affects neither the 10S-6S transition nor the myosin filament formation. Therefore, the inhibition of actin-activated ATPase activity of platelet myosin is not due to the change in the myosin conformation.
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PMID:Phosphorylation of bovine platelet myosin by protein kinase C. 234 43

The Ca2+-dependent regulation of contractile protein interactions in cardiac and vascular smooth muscle involves structurally related but distinct Ca2+ binding proteins. In vascular smooth muscle, Ca2+ binds to calmodulin, and Ca2+-calmodulin activates myosin light chain (MLC) kinase with ultimate stimulation of MLC phosphorylation and actin-myosin interactions. The largest class of inhibitors of vascular contractile protein interactions are the calmodulin antagonists which include certain Ca2+ entry blockers. Pharmacologically, some of these agents can be distinguished from pure Ca2+ entry blockers by being more effective vs. vasoconstrictor agents in vitro, less cardiac depressant, and more effective as platelet aggregation inhibitors. An even greater distinction from Ca2+ entry blockers is evident with another series of agents, isoquinolinesulfonamides, which directly inhibit protein kinase activity. Cardiac muscle myofibrillar regulation involves Ca2+ binding to troponin C (TnC). Some cardiotonics, such as Vardax and APP 201-533, increase the Ca2+ sensitivity of cardiac myofibrillar ATPase activity with a concomitant increase in Ca2+ binding to TnC. Several calmodulin antagonists, Ca2+ blockers, and structurally related agents differentially affect cardiac myofibrillar ATPase activity. Potency and efficacy of some of these stimulating agents is markedly greater than Vardax or APP 201-533. Mechanistically, all agents do not affect cardiac MLC phosphorylation, but directly enhance the Ca2+ sensitivity of ATPase activity. However, differential effects on basal and maximum ATPase activity by some agents suggest more complex or additional effects which are related to the type of agent as well as the species (dog vs. hamster). A major subcellular defect in congestive heart failure in various small animal models is a depressed maximum ATPase activity. Thus, a desired goal would be a pharmacological modulator which increases maximum ATPase activity, not necessarily Ca2+ sensitivity. In sum, it is possible to identify agents, Ca2+ binding protein modulators, which directly inhibit vascular smooth muscle and stimulate cardiac muscle contractile protein interactions. The potential advantages/disadvantages of this approach for vasodilator/cardiotonic drug development will have to await future development of novel compounds targeted specifically for these cellular regulatory processes.
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PMID:Pharmacological modulation of cardiac and vascular contractile protein function. 243 41

Phosphorylation of the regulatory light chains (RMLC) of nonmuscle myosin can increase the actin-activated ATPase activity and filament formation. Little is known about these regulatory mechanisms and how the RMLC are involved in ATP hydrolysis. To better characterize the nonmuscle RMLC, we isolated cDNAs encoding the Dictyostelium RMLC. Using an antibody specific for the RMLC, we screened a lambda gt11 expression library and obtained a 200-base-pair clone that encoded a portion of the RMLC. The remainder of the sequence was obtained from two clones identified by DNA hybridization, using the 200-base-pair cDNA. The composite RMLC cDNA was 645 nucleotides long. It contained 60 base pairs of 5' untranslated, 483 bases of coding, and 102 base pairs of 3' untranslated sequence. The amino acid sequence predicted an 18,300-dalton protein that shares 42% amino acid identity with Dictyostelium calmodulin and 30% identity with the chicken skeletal myosin RMLC. This sequence contained three regions that were similar to the E-F hand calcium-binding domains found in calmodulin, troponin C, and other myosin light chains. A sequence similar to the phosphorylation sequence found in chicken gizzard and skeletal myosin light chains was found at the amino terminus. Genomic Southern blot analysis suggested that the Dictyostelium genome contains a single gene encoding the RMLC. Analysis of RMLC expression patterns during Dictyostelium development indicated that accumulation of this mRNA increases just before aggregation and again during culmination. This pattern is similar to that obtained for the Dictyostelium essential myosin light chain and suggests that expression of the two light chains is coordinated during development.
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PMID:Dictyostelium discoideum myosin: isolation and characterization of cDNAs encoding the regulatory light chain. 255 Jul 95

The fiber type composition of two fast muscles of the chicken, namely, adductor superficialis (AS) and pectoralis major (PM) was examined by the histochemical myosin ATPase staining and immunochemical techniques using monoclonal antibodies (McAbs). Two new McAbs produced against the myosin of the anterior latissimus dorsi (ALD) muscle of the chicken and named ALD-122 and ALD-83 were characterized to be specific for myosin heavy chain (MHC) and for myosin light chain-1 respectively. They were used in conjunction with previously reported McAbs specific for slow MHC (ALD-47), fast MHC (MF-14) and fast light chain-2 (MF-5). By the histochemical ATPase test most muscle fibers of AS and PM muscles reacted as IIA and IIB respectively. By immunofluorescent staining with the anti-MHC McAbs, ALD-122 and MF-14, the fibers of AS muscle showed remarkable heterogeneity whereas PM muscle fibers reacted uniformly. Differences in the myosin light chain composition of AS and PM muscles were also found by SDS-gel electrophoresis and immunoblot analysis with the anti-light chain McAb, ALD-83. The study clearly indicated that the histochemically homogenous (type IIA) AS muscle is composed of several subpopulations of fibers which differ in their myosin composition and that this heterogeneity of the muscle is not simply due to presence of variable amounts of slow myosin in its fibers.
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PMID:Heterogeneity of fast-oxidative muscle fibers of chicken demonstrated by anti-myosin monoclonal antibodies. 273 24

The relaxant action of amiloride was investigated in the smooth muscles of guinea pig taenia ceci and chicken gizzard. Amiloride inhibited the contractions induced by high K+ (45.4 mM) and carbachol (10 microM) in the taenia with the concentrations needed to induce 50% inhibition (IC50) of approximately 41 microM. A prolonged incubation period (greater than 1 hr) was necessary to obtain the full inhibition of these contractions. The taenia gradually accumulated amiloride and the tissue/medium ratio exceeded 2.0 after a 120-min incubation period. Amiloride had no effect on the high K+-stimulated 45Ca++ uptake or the ATP content of the taenia. Amiloride inhibited the Ca++-induced contraction of the saponin-treated taenia with an IC50 of 186 microM. Amiloride (10-1000 microM) also inhibited superprecipitation and Mg++-adenosine triphosphatase activity of the gizzard native actomyosin as well as the phosphorylation of myosin light chain. The inhibition of the phosphorylation was antagonized competitively by ATP. Amiloride (1 mM) had no effect on the dephosphorylation of myosin light chain upon removal of Ca++ from reaction medium. Amiloride, at concentrations up to 1 mM, had not effect on calmodulin activity as monitored by the Ca++-calmodulin-activated erythrocyte membrane (Ca++ + Mg++)-adenosine triphosphatase and phosphodiesterase activities. In contrast to this, trifluoperazine inhibited the calmodulin activity at the concentration needed to inhibit the Ca++-induced contraction of the permeabilized taenia and the superprecipitation and the phosphorylation of myosin light chain of gizzard. We conclude that amiloride, unlike trifluoperazine, may inhibit directly the myosin light chain kinase activity to induce muscle relaxation.
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PMID:Inhibition by amiloride of contractile elements in smooth muscle of guinea pig taenia cecum and chicken gizzard. 282 5

Previously, we have shown that okadaic acid (OA), isolated from black sponge (Halichondria okadai) causes contraction even in the absence of Ca++ in the saponin-permealized taenia isolated from guinea pig cecum. In the present study, mechanism of action of OA was examined using native actomyosin extracted from chicken gizzard smooth muscle. In the absence of Ca++, OA (0.1-1 microM) induced superprecipitation and increased the Mg++-adenosine triphosphatase activity. The OA-induced superprecipitation was enhanced by Ca++ at a concentration (greater than 0.1 microM) which did not activate the calmodulin-dependent myosin light chain (MLC) kinase. The effect of OA was not affected by the calmodulin inhibitor, trifluoperazine, at a concentration (100 microM) needed to inhibit the Ca++-induced response, but was inhibited markedly by the nonselective kinase inhibitors, amiloride (1 mM) and K-252a (5 microM). The OA-induced superprecipitation in the absence of Ca++ was accompanied by phosphorylation of the 20 K dalton MLC, which also was enhanced by low concentration of Ca++ (greater than 0.1 microM). OA did not change the phosphatase activity which dephosphorylates the phosphorylated MLC. An activator of Ca++- and phospholipid-dependent protein kinase, 12-O-tetradecanoylphorbol 13-acetate (1 microM), did not modulate superprecipitation or phosphorylation of MLC in the presence and absence of OA. Furthermore, inhibitors of Ca++ and phospholipid-dependent protein kinase, 1-(5-isoquinoline-sulfonyl)-2-methylpiperazine dihydrochloride (400 microM) and polymyxin B (100 micrograms/ml), affected neither superprecipitation nor phosphorylation of MLC induced by OA. With a reconstituted system containing purified myosin and MLC kinase, OA induced only slight phosphorylation of MLC.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Calcium-independent phosphorylation of smooth muscle myosin light chain by okadaic acid isolated from black sponge (Halichondria okadai). 282 58


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