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)

The inhibitory effect of calmodulin antagonists, synthetic peptide analogs of the pseudosubstrate domain of smooth muscle MLC kinase, and an inhibitor based on the sequence of MLC were examined using bovine aortic actomyosin and isolated chicken gizzard MLC. Much lower concentrations of the peptides were necessary to inhibit actomyosin ATPase activity than to inhibit superprecipitation. In contrast, calmodulin antagonists inhibited both ATPase activity and superprecipitation at similar concentrations. The peptide analogs were competitive with isolated MLC, but not calmodulin, for inhibition of MLC kinase. These results suggest that in addition to the calmodulin dependence of MLC phosphorylation, a second calmodulin-like protein may be important in actin-myosin interactions. The data also suggest that the pseudosubstrate hypothesis may not completely account for regulation of MLC kinase activity.
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PMID:Peptide analogs of the pseudosubstrate domain of smooth muscle myosin light chain kinase inhibit actomyosin ATPase activity at concentrations that do not inhibit superprecipitation. 141 4

It seems clear that a simple Ca2+ dependent switch (MLC phosphorylation) cannot completely explain all of the disparate mechanical and energetic results obtained under numerous experimental conditions in numerous laboratories. Some of the problems of the simple switch model are that: 1. Force can be developed in the complete absence of increases in MLC phosphorylation; 2. Crossbridge cycling rate, as measured by either shortening velocity or directly by ATPase activity, can be regulated independent of changes in MLC phosphorylation; and 3. Ca2+ can directly influence both force and crossbridge cycling rate. Thus, we believe that there are two distinct Ca2+ dependent regulatory systems which normally act in parallel to contract smooth muscle. One of these is the Ca2+ dependent MLC phosphorylation-dephosphorylation. system which is likely to be responsible for the rapid development of force. The other is the hypothesized Ca2+ dependent system which is probably responsible for the slow development of force as well as the maintenance of previously developed force, represented in Figure 5 as K8. This second system involves a calmodulin-like protein with a higher Ca2+ sensitivity than that for the Ca(2+)-calmodulin-MLC kinase system. Under most conditions, the total force attained by smooth muscle in response to stimulation is the result of the concerted activation of both of these regulatory systems. The available information is consistent with this hypothesis of two regulatory systems functioning in parallel. In addition to the information presented in this chapter, work from a number of laboratories (Moreland and Ford, 1982; Fujiwara et al., 1989; Kitazawa et al., 1989; Somlyo et al., 1989; Kubota et al., 1990; Kitazawa and Somlyo, this volume) have suggested the possibility that a regulated MLC phosphatase may functionally alter the Ca2+ sensitivity of the contractile filaments. There is evidence suggesting that the sensitivity of MLC kinase to activation by Ca2+ and calmodulin may be regulated (Stull et al., this volume). Protein kinase C has been postulated to play an important role in the regulation of myofilament Ca2+ sensitivity (Nishimura et al., this volume). MgADP has been suggested to affect the kinetics of latchbridge attachment and detachment (Kerrick and Hoar, 1987; Nishimura and van Breemen, 1989). Cooperativity between crossbridges as described by Somlyo et al. (1988) and Siegman et al. (this volume) might also be an important component in the regulation of smooth muscle contraction.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Regulation of a smooth muscle contraction: a hypothesis based on skinned fiber studies. 180 23

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

In the urodelan amphibian Pleurodeles waltlii, spontaneous external metamorphosis was correlated with an increase in the serum level of thyroxine (T4). Within the same period, a change occurred in the myofibrillar ATPase profile of the dorsal skeletal muscle; fibres of larval type were gradually replaced by transitional fibres (type IIC), then by adult fibres of the types I, IIA, and IIB. Likewise, a myosin isoenzymic transition was observed. In larval animals, myosin electrophoresis revealed 3 bands corresponding with isoforms having identical heavy chains (MHC), but different light chains (MLC). In the course of metamorphosis, the 3 larval isomyosins were replaced by 3 isoforms having the adult type MHC and different motility. In a related neotenic species, Ambystoma mexicanum, no spontaneous anatomic metamorphosis occurred; at the time it should theoretically take place, the serum T4 level remained low. The ATPase profile was modified, but transitional fibres that replaced the initial larval types appeared to be persistent, and adult fiber types appeared only in a small amount. Myosin isoenzymic transition was also incomplete, larval isoforms were still distinguished in the neotenic adults. Similar persistence of larval characters was observed in adult Proteus anguinus, a perennibranch that never undergoes anatomical metamorphosis. Experimental hypothyroidian Pleurodeles waltlii displayed no external metamorphosis, only the larval fibre types and isomyosins were detected in those animals. External metamorphosis was induced in Ambystoma mexicanum by a triiodothyronine treatment. A complete myosin isoenzymic transition was observed in metamorphosed animals. These results tend to indicate that a moderate increase in the level of thyroid hormones is sufficient to determine the production of the adult type MHC molecules and the differentiation of the corresponding myofibrillar types in the skeletal dorsal muscle of amphibians, while a marked increase would be necessary for repressing the initial larval feature.
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PMID:[Hormonal determination of the differentiation of striated skeletal muscle in urodele amphibians]. 297 2

The basal body cage is a fibrillar chamber which surrounds each basal body in the ciliate cytoskeleton. The function of this chamber is unknown. In Tetrahymena, the cage contains actin filaments which connect the cage to triplet microtubules. In this study, we have examined the cage for the presence of myosin. Skeletal muscle myosin-II heavy and light chains were used to affinity-purify anti-MHC and anti-MLC antibodies, respectively, from an antiserum raised against Tetrahymena oral apparatus proteins. On western immunoblots of ATP-solubilized Tetrahymena proteins, the anti-MHC antibody detected a putative myosin heavy (180 kDa) chain, and the anti-MLC antibody detected a putative myosin light (18 kDa) chain. The anti-MHC antibody specifically labeled the AI zone of sarcomeres. In cosedimentation assays with an ATP-solubilized protein fraction, the 180 kDa polypeptide associated with skeletal muscle actin filaments in an ATP-dependent manner. The sedimented actin filaments appeared to be organized into bundles. Immunodepletion of the 180 kDa rendered the ATP-solubilized protein fraction ineffective in bundling actin filaments in a cosedimentation assay. ATP-solubilized Tetrahymena proteins, which included the 180 kDa polypeptide, exhibited F-actin-stimulated, Mg2+ ATPase activity and K+, EDTA ATPase activity which are characteristic of myosin ATPases. Immunodepletion of the 180 kDa polypeptide reduced the F-actin, Mg2+ ATPase activity of the ATP-solubilized protein fraction by more than 80%. Based on these various observations, we conclude that the 180 kDa polypeptide is a putative myosin heavy chain, probably a myosin-II and that the 18 kDa polypeptide is probably a myosin-II light chain. We have used the affinity-purified, anti-myosin antibodies with immunofluorescence microscopy and immunogold electron microscopy to map the location of the putative myosin heavy and light chains in Tetrahymena. Immunofluorescence microscopy showed that the anti-myosin antibodies localized to Tetrahymena somatic and oral region basal bodies. At the ultrastructural level, the anti-myosin antibodies localized to filaments in the basal body-cage complex. The labeling patterns with both anti-myosin antibodies were identical to the labeling pattern observed with an anti-actin antibody reported in a previous study. The co-localization of myosin and actin argue for a motility system within the basal body-cage complex.
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PMID:Putative myosin heavy and light chains in Tetrahymena: co-localization to the basal body-cage complex and association of the heavy chain with skeletal muscle actin filaments in vitro. 762 16

Sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE), glycerol SDS-PAGE, two-dimensional electrophoresis, and protein immunoblotting techniques were used to identify myosin heavy chain (MHC) and light chain (MLC) isoforms in limb and masticatory muscles of the cat and American opossum. The fibre types in which these isoforms are expressed were identified by histochemistry and immunohistochemistry. Antibodies specific for the type IIM MHC isoform characteristic of cat jaw-closing muscles and the type I MHC isoform were produced and characterized. The IIM antibody stained the majority of fibres found in the jaw-closing muscles of both species. These IIM-containing fibres characteristically had a histochemical ATPase that remained active after both acid and alkali pre-incubations. A minority of type I fibres was also present in cat jaw-closing muscles, and these reacted positively with antibody specific for type I MHC. It was confirmed that the vast majority of fibres in the cat jaw-closing muscles contained only the characteristic masticatory MHC (IIM) and masticatory MLCs (LC1m and LC2m). These muscles did not contain either the type II fibre isoforms of limb muscles or the atrial cardiac (alpha-cardiac) MHC. The type IIM MHC could also be identified in jaw-closing muscles of the opossum. Two-dimensional gel electrophoresis was used to identify the MLC composition of single, histochemically defined, type I fibres in the cat soleus and deep masseter. The type I fibres of limb muscle contained the usual slow MLCs, but type I fibres from the jaw-closing muscles contained only the masticatory light chains.
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PMID:Myosin expression in the jaw-closing muscles of the domestic cat and American opossum. 763 44

1. Myofibrillar ATPase activity, isometric tension (Po) and unloaded shortening velocity (Vo) were determined in single skinned fibres isolated from rat hindlimb muscles during maximal calcium activation at 12 degrees C. In each fibre, myosin heavy chain (MHC) isoforms were identified using electrophoresis and immunocytochemistry. ATPase activity was determined spectrophotometrically from NADH oxidation in a coupled enzyme assay. 2. On the basis of their MHC isoform composition, the fibres (n = 102) were divided into five groups containing the slow isoform, I MHC, or one of the fast isoforms, IIB MHC, IIA MHC, IIX MHC, or a mixture of the latter three. ATPase activity was significantly higher in IIB than in 2X and IIA fibres (0.230 +/- 0.010, 0.178 +/- 0.023 and 0.168 +/- 0.026 nmol mm-3 s-1, respectively). Mixed fibres had intermediate values. ATPase activity in slow fibres was considerably less (0.045 +/- 0.006 nmol mm-3 s-1). 3. The ratio between ATPase activity and Po, i.e. tension cost, was found to be 2.90 +/- 0.09, 2.56 +/- 0.14, 1.89 +/- 0.22, 1.52 +/- 0.13 and 0.66 +/- 0.004 pmol ATP nM-1 mm-1 s-1 in IIB, mixed, IIX, IIA and slow fibres, respectively. All the differences were statistically significant except that between IIA and IIX fibres. 4. Within each group of fibres with the same MHC composition, ATPase activity was found to correlate with Po, but not Vo. However, ATPase activity was found to correlate with Vo when all the fibre types were pooled together. 5. In thirty-seven fast fibres the MLC ratio, i.e. the proportion of the fast alkali light chain isoform, MLC3f, to the amount of the regulatory light chain, MLC2f, was determined. IIB fibres had the highest proportion of MLC3f and IIA fibres, the lowest. 6. A multiple regression analysis, used to distinguish between the effects of MHC and MLC composition, showed that ATPase activity was insensitive to the MLC ratio, whereas it had a significant impact on Vo. 7. The results obtained in this study indicate that in rat skeletal muscle fibres: (a) ATPase activity during isometric contractions and tension cost are strongly dependent on MHC isoform composition, and (b) there is no evidence that the alkali MLC ratio is a determinant of ATPase activity.
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PMID:Myofibrillar ATPase activity during isometric contraction and isomyosin composition in rat single skinned muscle fibres. 770 34

The N-terminal region of skeletal myosin light chain-1 (MLC-1) binds to the C terminus of actin, yet the functional significance of this interaction is unclear. We studied a fragment (MLC-pep; residues 5-14) of the ventricular MLC-1. When added to rat cardiac myofibrils, 10 nM MLC-pep induced a supramaximal increase in the MgATPase activity at submaximal Ca2+ levels with no effect at low and maximal Ca2+ levels. A nonsense, scrambled sequence peptide had no effect at any pCa value. MLC-pep did not affect myosin KEDTA and CaATPase activities or actin-activated MgATPase activities in the absence or presence of tropomyosin. The MLC-pep did not alter the ability of troponin I to inhibit MgATPase activity. Moreover, when troponin I and troponin C were extracted from the myofibrils, the MLC-pep lost its ability to stimulate the ATPase rate. This effect was fully restored upon reconstitution of the extracted myofibrils with troponin I-troponin C complex. Thus, activation of MgATPase activity by the peptide required a full complement of thin filament regulatory proteins. Interestingly, the stimulatory effect occurred at a ratio of 4 peptides to 1 thin filament, suggesting that the peptide engages in a highly cooperative process that may involve activation of the entire thin filament.
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PMID:An essential myosin light chain peptide induces supramaximal stimulation of cardiac myofibrillar ATPase activity. 890 Jan 93

1. ATP consumption and force development were determined in single skinned muscle fibres of the rat at 12 degrees C. Myofibrillar ATPase consumption was measured photometrically from NADH oxidation which was coupled to ATP hydrolysis. Myosin heavy chain (MHC) and light chain (MLC) isoforms were identified by gel electrophoresis. 2. Slow fibres (n = 14) containing MHCI and fast fibres (n = 18) containing MHCIIB were compared. Maximum shortening velocity was 1.02 +/- 0.63 and 3.05 +/- 0.23 lengths s-1, maximum power was 1.47 +/- 0.22 and 9.59 +/- 0.84 W l-1, and isometric ATPase activity was 0.034 +/- 0.003 and 0.25 +/- 0.01 mM s-1 in slow and in fast fibres, respectively. 3. In fast as well as in slow fibres ATP consumption during shortening increased above isometric ATP consumption. The increase was much greater in fast fibres than in slow fibres, but became similar when expressed relative to the isometric ATPase rate. 4. Efficiency was calculated from mechanical power and free energy change associated with ATP hydrolysis. Maximum efficiency was larger in slow than in fast fibres (0.38 +/- 0.04 versus 0.28 +/- 0.03) and was reached at a lower shortening velocity. 5. Within the group of fast fibres efficiency was lower in fibres which contained more MLC3f. We conclude that both MHC and essential MLC isoforms contribute to determine efficiency of chemo-mechanical transduction.
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PMID:Chemo-mechanical energy transduction in relation to myosin isoform composition in skeletal muscle fibres of the rat. 926 23

These experiments examined the myosin phenotype and bioenergetic enzyme activities in rat respiratory muscles. Muscle samples were removed from adult female Sprague-Dawley rats (N = 8) and analyzed to determine the myosin heavy chain (MHC) and light chain (MLC) isoform content as well as the activities of myofibrillar ATPase (mATPase), citrate synthase (CS; Krebs cycle enzyme), and lactate dehydrogenase (LDH; glycolytic enzyme). Analysis revealed that CS activity and the % type I MHC and %IId MHC isoforms were greater in the costal diaphragm (CO-D) compared with those in the crural diaphragm (CR-D). In contrast, the % type IIb MHC was higher in the CR-D compared with that in the CO-D. LDH and mATPase activity were lower in both the CO-D and CR-D compared with that in the parasternal intercostals (PI), external intercostals (EI), internal intercostals (II), rectus abdominis (RA), and sternomastoid (SM) muscles. CS activity, % type I MHC, %IIa MHC, and the ratio of slow to total alkali MLC (1s/1s + 1f + 3f) were greater in the CO-D and CR-D compared with those in all other respiratory muscles. The RA contained the highest (P < 0.05) % type IIb MHC and lowest CS activity compared with that in all other muscles. Finally, CS activity, mATPase activity, and MHC phenotype did not differ among the PI, EI, II, and SM muscles. These differences in biochemical properties provide the muscles of the respiratory pump with great versatility in functional properties.
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PMID:Myosin phenotype and bioenergetic characteristics of rat respiratory muscles. 943 89


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