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)

Thiosphosphorylated smooth muscle myosin and skeletal muscle myosin, both of which express Ca(2+)-independent actin-activated MgATPase activity, were used to examine the functional effects of calponin and caldesmon separately and together. Separately, calponin and caldesmon inhibited the actin-activated MgATPase activities of thiophosphorylated smooth muscle myosin and skeletal muscle myosin, calponin being significantly more potent in both systems. Calponin-mediated inhibition resulted from the interaction of calponin with actin since it could be reversed by increasing the actin concentration. Caldesmon had no significant influence on the calponin-induced inhibition of the smooth muscle actomyosin ATPase, nor did calponin have a significant effect on caldesmon-induced inhibition. In the skeletal muscle system, however, caldesmon was found to override the inhibitory effect of calponin. This difference probably reflects the lower affinity of skeletal muscle actin for calponin compared with that of smooth muscle actin. Calponin inhibition of skeletal muscle actin-activated myosin MgATPase was not significantly affected by troponin/tropomyosin, suggesting that the thin filament can readily accommodate calponin in addition to the troponin complex, or that calponin may be able to displace troponin. Calponin also inhibited acto-phosphorylated smooth muscle heavy meromyosin and acto-skeletal muscle heavy meromyosin MgATPases. The most appropriate protein preparations for analysis of the regulatory effects of calponin in the actomyosin system therefore would be smooth muscle actin, tropomyosin and thiophosphorylated myosin, and for analysis of the kinetic effects of calponin on the actomyosin ATPase cycle they would be smooth muscle actin, tropomyosin and phosphorylated heavy meromyosin, due to the latter's solubility.
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PMID:A comparison of the effects of calponin on smooth and skeletal muscle actomyosin systems in the presence and absence of caldesmon. 147 86

The mechanism for the potentiation of the actin-activated ATPase of smooth muscle myosin by tropomyosin is investigated using smooth muscle actin, tropomyosin, and heavy meromyosin. In the presence of tropomyosin, an increase in Vmax occurs with no effect on KATPase and Kbinding at 20 mM ionic strength. Utilizing N-ethylmaleimide-treated subfragment-1, which forms rigor complexes with actin in the presence of ATP but does not have ATPase activity, experiments were carried out to determine if the tropomyosin-actin complex exists in both the turned-off and turned-on forms as in the skeletal muscle system. At both 60 and 100 mM ionic strengths, the presence of rigor complexes on the smooth muscle actin filament containing bound tropomyosin causes a 2-3-fold increase in Vmax and about a 3-fold increase in KATPase, resulting in about a 4-fold increase in ATPase activity at moderate actin concentration. The increase in KATPase is correlated with an increase in Kbinding. The finding that rigor complexes increase Vmax and the binding constant for heavy meromyosin to tropomyosin-actin at an ionic strength close to physiological conditions indicates that the tropomyosin-actin complex can be turned on by rigor complexes in a cooperative manner. However, in contrast to the situation in the skeletal muscle system, the increase in KATPase is associated with a corresponding increase in Kbinding. Furthermore, there is only a 3-fold increase in KATPase in the smooth muscle system rather than a 10-fold increase as in the skeletal muscle system.
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PMID:Cooperativity of actin-activated ATPase of gizzard heavy meromyosin in the presence of gizzard tropomyosin. 213 24

High-Mr caldesmon, which is involved in smooth muscle contraction, was phosphorylated by protein kinase C. By chymotryptic digestion, actin- and calmodulin-binding assays and immunoprecipitation with the antibody to the C-terminal 35-kDa fragment, we have identified that all phosphate groups are incorporated exclusively into this fragment, which is the functional domain for binding actin and calmodulin. Phosphorylation of high-Mr caldesmon and its C-terminal 35-kDa fragment reduced their binding abilities to both F-actin and calmodulin. Further, their inhibitory effects on the actin-activated ATPase activity of gizzard myosin were also reversed in proportion to the degree of phosphorylation. These results suggest that phosphorylation of high-Mr caldesmon by protein kinase C, which is restricted within the C-terminal 35-kDa domain, results in the modulation of its activity in the smooth muscle actin--myosin interaction.
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PMID:Phosphorylation of high-Mr caldesmon by protein kinase C modulates the regulatory function of this protein on the interaction between actin and myosin. 213 5

Our results indicate that the kinetic "latch" model of Hai & Murphy is not very sensitive to the proportion of ATP assigned to crossbridges relative to that ascribed to MLC phosphorylation/dephosphorylation. Thus the basis for the relatively low efficiency of smooth muscle, attributed to high MLC phosphorylation/dephosphorylation in this model, remains open to question. Moreover, this model, or any model with mixed populations of crossbridges with differing cycle rates and/or high MLC phosphorylation/dephosphorylation rates is unlikely to account for the observed linearity of JATP and stress reported for many smooth muscles. Our studies comparing the heat production of intact and skinned smooth muscle indicate that the ATPase associated with myosin phosphorylation/dephosphorylation is unlikely to be a major factor in the tension cost of intact smooth muscle. Thus it would appear that energetics places considerable constraints on current theories of crossbridge regulation. Our modelling (Paul, 1989) suggests that it may be time to reevaluate Bozler's original hypothesis that a high attachment:detachment rate ratio for smooth muscle actin-myosin interaction may be sufficient to explain the energetics of smooth muscle.
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PMID:Smooth muscle energetics: testing theories of crossbridge regulation. 232 Jun 7

A Ca2+-dependent actin-severing 84K Mr protein prepared from bovine aorta caused four-fold activation of smooth muscle actin-activated myosin ATPase at a 1/10(2) molar ratio to actin in the presence of tropomyosin and light chain kinase-calmodulin in a Ca2+-dependent manner, while it inhibited it markedly at a 1/5 molar ratio. Purified actin-tropomyosin filaments under the experimental ATPase conditions were distributed in a range of more than 10 micron in length and the addition of the 84K Mr protein changed the filament length to around 1 micron at a 1/10(2) molar ratio to actin or less than 50 nm at a 1/5 molar ratio in the presence of Ca2+. However, the apparent length of actin filaments alone does not appear to be responsible for the activation of ATPase activity, since in the absence of tropomyosin, the ATPase activation was much less in spite of actin filament length changes. These results indicate the possibility that the 84K Mr protein plays an important role with tropomyosin in at least in vitro smooth muscle actin-myosin interaction.
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PMID:Enhancement of actin-activated myosin ATPase by an 84K Mr actin-binding protein in vertebrate smooth muscle. 293 81

The binding of gizzard tropomyosin to gizzard F-actin is highly dependent on free Mg2+ concentration. At 2 mM free Mg2+, a concentration at which actin-activated ATPase activity was shown to be Ca2+ sensitive, a molar ratio of 1:3 (tropomyosin:actin monomer) is required to saturate the F-actin with tropomyosin to the stoichiometric ratio of 1 mol of tropomyosin to 7 mol of actin monomer. Increasing the Mg2+ could decrease the amount of tropomyosin required for saturating the F-actin filament to the stoichiometric level. Analysis of the binding of smooth muscle tropomyosin to smooth muscle actin by the use of Scatchard plots indicates that the binding exhibits strong positive cooperativity at all Mg2+ concentrations. Calcium has no effect on the binding of tropomyosin to actin, irrespective of the free Mg2+ concentration. However, maximal activation of the smooth muscle actomyosin ATPase in low free Mg2+ requires the presence of Ca2+ and stoichiometric binding of tropomyosin to actin. The lack of effect of Ca2+ on the binding of tropomyosin to actin shows that the activation of actomyosin ATPase by Ca2+ in the presence of tropomyosin is not due to a calcium-mediated binding of tropomyosin to actin.
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PMID:Role of tropomyosin in smooth muscle contraction: effect of tropomyosin binding to actin on actin activation of myosin ATPase. 294 Oct 78

Using a reconstituted system in which myosin was preferentially phosphorylated, we examined the regulatory action of caldesmon150 on the smooth muscle actin-myosin interaction. Caldesmon150 inhibited the tropomyosin-enhanced actomyosin ATPase activity in a Ca2+-independent manner. This inhibitory effect of caldesmon150 was observed to be overcome by the addition of calmodulin in a Ca2+-dependent manner. In accordance with the observations of ATPase activity, we demonstrated evidence that the regulatory action of caldesmon150 on the actin site was mainly through control of the tropomyosin-enhanced actin-myosin interaction and calmodulin confers the Ca2+-sensitivity upon the caldesmon150 action determined by the cosedimentation method.
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PMID:Caldesmon150 regulates the tropomyosin-enhanced actin-myosin interaction in gizzard smooth muscle. 406 43

Troponin was isolated from the thin filaments of ascidian smooth muscle and separated into three components by ion-exchange chromatography, the molecular weights of which were 33,000, 24,000, and 18,000, respectively. The three components were designated as troponin t (TN-T), troponin I (TN-I), and troponin C (TN-C) in order of molecular weight, since each component had properties similar to those of the respective components of vertebrate skeletal-muscle troponin. The ascidian troponin or the mixture of the three components conferred Ca2+-sensitivity on reconstituted rabbit actomyosin in the presence of tropomyosin. One of the characteristics of the ascidian troponin was Ca2+-dependent activation of actin-myosin interaction in collaboration with tropomyosin, whereas its inhibitory action on the actomyosin ATPase in the absence of Ca2+ was less remarkable. From this, it is concluded that in the ascidian smooth muscle actin-myosin interaction is regulated by an actin-linked troponin-tropomyosin system, but the ascidian troponin acts as a Ca2+-dependent activator of an actomyosin system.
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PMID:Troponin and its components from ascidian smooth muscle. 611 58

Four renal cell lines were derived from glomeruli, proximal, distal, and cortical collecting tubules microdissected from the kidneys of transgenic mice carrying the temperature-sensitive mutant of the simian virus 40 large T antigen under the control of the vimentin promoter. All four cell lines contained large T antigen in their nuclei, grew rapidly, and contained vimentin filaments when grown in serum-enriched medium at the permissive temperature of 33 degrees C. The glomerular cell line formed multiple layers of cells and contained smooth muscle actin and desmin filaments, features of mesangial cells. The three tubule cell lines formed monolayers of polarized cuboid cells separated by tight junctions and having a patchy distribution of cytokeratins K8-K18. A shift from 33 degrees C to the restrictive temperature (39.5 degrees C) stopped cell growth in all cell lines and caused profound changes in the content of intermediate filaments. Vimentin was still present in mesangial-like cells, but the proximal, distal, and collecting tubule cells contained uniform networks of cytokeratins K8-K18 and desmoplakin I and II around the cell peripheries. Potassium transport, mediated by Na+-K+ ATPase pumps and specific cAMP hormonal sensitivities, significantly increased in proximal, distal, and collecting tubule cells when shifted from 33 degrees C to 39.5 degrees C. Thus, the temperature-dependent inactivation of large T antigen, responsible for the arrest of cell growth, did not affect the phenotype of mesangial-like glomerular cells but induced some changes in the expression of intermediate filaments and restored, at least partially, the main parental cell-specific functions in proximal, distal, and collecting tubule cultured cells.
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PMID:Relationships between intermediate filaments and cell-specific functions in renal cell lines derived from transgenic mice harboring the temperature-sensitive T antigen. 869 37

Fibroblasts were derived from dermis and scar of a 47-year-old white man with a recurrent incisional hernia as a result of fractured ribs. The scar was thin and stretched, suggesting a defect in the maturation of granulation tissue. After surgical repair, biopsy specimens of discarded scar and skin were used to generate fibroblast cell lines. Fibroblasts maintained in medium containing 10% fetal bovine serum and antibiotic were studied between their third and eighth passage. By phase contrast microscopy, no structural differences were obvious, but it was noted that to pass scar fibroblasts, a more aggressive trypsin regimen was required. Immunohistologic and Western blot analysis of patient scar fibroblasts showed (1) more a smooth muscle actin within stress fibers, (2) increased expression of the vitronectin integrin receptor alpha(v) (CD 51), and (3) reduced expression of the collagen integrin receptor alpha2 (CD 49b). The expression of vinculin from focal adhesions or a tubulin from microtubules was the same among cell lines. Contractions of scar and dermal fibroblast-populated collagen lattice were compared. At 24 hours, contractions were 69 percent with newborn fibroblasts (normal); 68 percent for patient dermal fibroblasts; and only 48 percent for patient scar fibroblasts. The retarded contraction of scar fibroblast-populated collagen lattice was significant (p > or = 0.002). Myosin ATPase activity, critical for lattice contraction, and cell migration were equivalent among all cell lines. A plausible mechanism for the retardation of scar lattice contraction is disruption of fibroblasts and collagen interactions, for which the attachment of cells to collagen is altered. It is proposed that either the decrease in the expression of collagen integrin receptor alpha2 (CD 49b), an increase in the expression of the vitronectin receptor alpha(v) (CD 51), or a combination of both is responsible for disruption of collagen fibroblast interactions.
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PMID:Differences between scar and dermal cultured fibroblasts derived from a patient with recurrent abdominal incision wound herniation. 1051 24


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