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 shown in genetic myopathic hamsters that cardiac myofibrillar ATPase regulation by calcium is altered and that there are shifts in myosin isozyme distribution (V1----V3) suggesting abnormalities in multiple components of the contractile apparatus. To focus more on the regulatory proteins (troponin and tropomyosin), individual proteins of the skeletal and cardiac actomyosin system were reconstituted under controlled conditions. In this way, myosin plus actin and troponin-tropomyosin from the normal and myopathic animals could be studied enzymatically. The proteins were isolated from the skeletal or cardiac muscle of random-bred control and cardiomyopathic hamsters (BIO 53:58) at 7 months of age. Sodium dodecyl sulfate gel electrophoretic patterns indicated differences in the troponin I and troponin C regions of myopathic skeletal muscle, but cardiac samples from control and myopathic hamsters showed similarities in their mobilities. This suggests the possibility of different cardiac isozymes in the regulatory protein complex, as reported in our previous studies of cardiac myosin in cardiomyopathy. Calcium sensitivity was markedly decreased in the actomyosin reconstituted with troponin-tropomyosin from skeletal as well as cardiac muscle from myopathic animals. In summary, our data show that the regulatory proteins in skeletal and cardiac muscle of the myopathic hamsters have decreased inhibitory action on Mg2(+)-actomyosin ATPase activity. This loss of calcium regulation along with shifts in cardiac myosin heavy chain may be partially responsible for the impaired cardiac function in the hearts of myopathic hamsters.
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PMID:Regulatory proteins in hamster cardiomyopathy. 213 21

There is evidence for the existence of developmental changes in expression of troponin I (TNI) in cardiac thin filaments; however, regulation of TNI expression has not been described. We tested whether thyroid state affects expression of TNI using neonatal and adult rats made hypothyroid by treatment with 6-n-propyl-2-thiouracil. Polyacrylamide gels of myofibrils from hearts of 7-, 14-, 21-, and 28-day-old animals indicated that both euthyroid and hypothyroid rats display a developmental shift toward the adult form of TNI. However, hypothyroid rats displayed a lower percentage of adult TNI at each age studied. When adult rats were made hypothyroid, the proportion of adult TNI decreased slightly. Thin-filament activity was determined from measurements of the effect of acidic pH on calcium activation of myofibrillar ATPase activity. Sensitivity to acidic pH was measured by the magnitude of shift in pCa50 (-log of half-maximally activating molar Ca2+) between pH 7.0 and 6.5. Euthyroid rats displayed developmental increases in pH sensitivity. At 7, 14, and 28 days of development, shifts in pCa50 were 0.11, 0.38, and 0.43 units, respectively. Hypothyroid rats displayed less pH sensitivity with pCa50 shifts of 0.07, 0.21, and 0.15 units at 7, 14, and 28 days of development. Adult hypothyroid rats displayed a 0.38-unit shift in pCa50, whereas euthyroid adults displayed a 0.44-unit shift. Our results indicate that pH sensitivity and expression of cardiac TNI are influenced by developmental stage and hormonal status.
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PMID:Effect of thyroid status on thin-filament Ca2+ regulation and expression of troponin I in perinatal and adult rat hearts. 214 96

We probed possible developmentally related changes in thin filament activity in rat hearts with the aid of calmidazolium (CDZ). CDZ is a calmodulin antagonist that also binds to troponin C and stimulates Ca2+ troponin C-dependent activation of cardiac myofibrillar contractile activity. In paired experiments, we compared the effects of 10, 30, 50, 70, and 100 microM CDZ on Mg2(+)-dependent ATPase activity of myofibrillar preparations from adult and neonatal rat hearts. Over the dose-response curve, the ATPase activity of neonatal myofibrils was significantly less stimulated than was the ATPase activity of the adult preparations. To know whether this difference in response to CDZ was related to differences in the thin or thick filaments, we studied hybrid adult and neonatal myofibrillar preparations. These hybrid myofibrils had native thin filaments, but the thick filaments were displaced with rabbit skeletal myosin. The relative insensitivity of the neonatal preparations to the effect of CDZ was retained in the hybrid myofibrils. This suggested that developmental transitions in the population of thin filament proteins are responsible for the difference between adult and neonatal myofibrils in their response to CDZ. Recently, we and others have reported developmental switching of troponin I isoforms in the rat heart. Since troponin I reacts strongly with troponin C in a Ca2(+)-dependent manner, we speculate that developmentally related changes in troponin I isoforms may contribute to the differential effect of CDZ in neonatal cardiac myofibrils.
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PMID:Developmental difference in the stimulation of cardiac myofibrillar Mg2(+)-ATPase activity by calmidazolium. 214 10

The interaction between actin and caldesmon that is associated with the inhibition of actomyosin ATPase activity in smooth muscle has been studied using 1H-NMR spectroscopy. Binding studies using the intact molecules were complemented by the use of thrombic cleavage fragments of both turkey and chicken gizzard caldesmon as well as defined peptides of actin, in order to investigate the conformational properties of caldesmon and to localise regions of the primary structures that participate in protein-protein contacts. The binding of caldesmon is shown to involve distinct segments on the N-terminal region (residues 1-44) of actin, as previously observed for the inhibitory component of the thin filament of striated muscle, troponin I [Levine et al. (1988) Eur. J. Biochem. 153, 389-397]. The comparable structural properties of these tissue-specific inhibitors of actomyosin ATPase and the similarities in their mode of interaction at the N-terminal region of actin suggest common aspects to the structural mechanism for thin-filament regulation in smooth and striated muscle. Unlike the inhibitory interaction of troponin I, however, the binding of caldesmon to the N-terminal region of actin directly involves groups within residues 20-41 of actin that are also recognised by myosin subfragment 1. The complementary segment of caldesmon has been localised to a 15-kDa thrombic fragment (residues 483-578) derived from the N-terminal portion of a 35-kDa proteolytic cleavage product from the C-terminal of caldesmon whose interaction with actin is modulated by calmodulin. The results are discussed in relation to the calcium-mediated mechanism for thin-filament regulation in smooth and striated muscle.
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PMID:Structural study of gizzard caldesmon and its interaction with actin. Binding involves residues of actin also recognised by myosin subfragment 1. 214 15

A sequence homology has been noted between the carboxyl quarter of the catalytic gamma subunit of phosphorylase kinase and the region of troponin I coded by exon VII. Because this portion of troponin I contains the inhibitory region that interacts with actin and troponin C, we have examined whether the gamma subunit of phosphorylase kinase can functionally mimic troponin I by also interacting with actin and troponin C. We have found that troponin C not only activates the isolated gamma subunit of phosphorylase kinase but also binds with approximately the same affinity as calmodulin. Although actin had no effect on the activity of the gamma subunit alone, it did inhibit the activity of gamma-calmodulin and gamma-troponin C complexes. Conversely, the gamma subunit was able to inhibit actomyosin ATPase in a process that could be overcome by calmodulin. These results suggest that actin and calmodulin (or troponin C) compete for binding to the gamma subunit. Moreover, the structural and functional similarities between the gamma subunit and troponin I suggest that the gamma subunit of phosphorylase kinase may have evolved from the fusion of a protein kinase protogene with a progenitor of exon VII of troponin I.
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PMID:Functional and structural similarities between the inhibitory region of troponin I coded by exon VII and the calmodulin-binding regulatory region of the catalytic subunit of phosphorylase kinase. 240 8

Myelin basic protein (MBP) binds to both skeletal muscle and brain tropomyosin resulting in the formation of paracrystalline tactoids in the absence of divalent cations and at neutral pH. Both types of tropomyosin reduce the inhibition of the ATPase activity of actomyosin caused by MBP. On the other hand, MBP alters the effect of both brain and skeletal muscle tropomyosins on the actomyosin ATPase, even though MBP and tropomyosin bind independently to actin. We conclude that MBP cannot substitute for troponin I in the regulation of the action of tropomyosin on actin.
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PMID:Interaction of tropomyosin with myelin basic protein and its effect on the ATPase activity of actomyosin. 243 9

The present study was designed to examine the relation between the loss of Ca2+ uptake activity and the change of protein phosphorylation in sarcoplasmic reticulum from ischemic myocardium. Ischemic (0.5, 1 and 2 h duration) and non-ischemic tissue samples were taken from the coronary-ligated porcine left ventricle and sarcoplasmic reticulum fractions were isolated. The membranes were tested for Ca2+ uptake and ATPase activities and phosphorylation of phospholamban. The in vitro 32P incorporation into phospholamban in the presence of cAMP plus the catalytic subunit of cyclic AMP dependent protein kinase became markedly reduced depending on the duration of ischemia. The activities of the Ca2+ pump (Ca2+ uptake and ATPase) were also decreased. The 32P incorporation into the myofibrillar component troponin I, which is also a specific substrate for catalytic subunit, was not affected by ischemia. The reduction of the Ca2+ pump activity correlated with the reduction of 32P incorporation into phospholamban. It is postulated that the ischemia induced inactivation of the Ca2+ pump is not only a consequence of specific loss of enzyme activity, but it is also caused by altered characteristics of phospholamban.
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PMID:Calcium transport and phospholamban in sarcoplasmic reticulum of ischemic myocardium. 252 77

As an extension of our previous reports that cardiac and skeletal muscle troponin I (Tn-I) and troponin T (Tn-T) are excellent substrates for protein kinase C (PKC) (Katoh, N., Wise, B. C., and Kuo, J. F. (1983) Biochem. J. 209, 189-195; Mazzei, G. J., and Kuo, J. F. (1984) Biochem. J. 218, 361-369), we have now determined that PKC phosphorylated serine 43 (and/or serine 45), serine 78, and threonine 144 in the free Tn-I subunit and threonine 190, threonine 199, and threonine 280 in the free Tn-T subunit of bovine cardiac troponin. PKC appeared to phosphorylate the same sites of the subunits present in the form of the troponin complex, as indicated by the similarity in the two-dimensional phosphopeptide maps. Although some of the phosphorylation sites were shared by other classes of protein kinases, PKC exhibited a distinct substrate specificity. It was also noted that phosphorylated serine and threonine residues in Tn-I and Tn-T had neighboring basic amino acid residues separated by 1 or 2 other residues both at the amino and carboxyl termini, in agreement with the conclusion of House et al. (House, C., Wettenhall, R. E. H., and Kemp, B. E. (1987) J. Biol. Chem. 262, 772-777) based upon their studies on other substrate proteins. Several peptides having sequences around the phosphorylating sites have been synthesized. The phosphorylation experiments indicated that these peptides were substrates for PKC, and their relative substrate activity (determined by the ratios of Vmax/Km) compared with other proteins, in descending order, was Tn-I = Tn-I(134-154) greater than Tn-T much greater than histone H1 greater than Tn-I(33-35) approximately Tn-T(268-284) greater than Tn-T(179-198) approximately Tn-T(191-209). It is suggested that PKC phosphorylation of Tn-I and Tn-T could be biologically significant in terms of possible modifications in interactions among the individual contractile protein components as well as the Ca2+ sensitivity and activity of actomyosin ATPase.
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PMID:Identification of sites phosphorylated in bovine cardiac troponin I and troponin T by protein kinase C and comparative substrate activity of synthetic peptides containing the phosphorylation sites. 258 39

Certain forms of cardiac failure appear to be associated with a decrease in the Ca++ sensitivity of the contractile structures, possibly due to troponin I phosphorylation. Interference of cardiotonic drugs with myofibrillar Ca++ activation instead of enhancement of Ca++ influx may therefore provide a more causal therapeutic concept in the treatment of cardiac insufficiency. APP 201-533 (3-Amino-6-methyl-5-phenyl-2(1H)-pyridinone) (the structure of which is shown below) is a novel cardiotonic agent acting neither via beta adrenoceptor stimulation nor inhibition of Na+/K+ ATPase. In the 100 microM concentration range, it increases the Ca++ sensitivity and the Ca++ affinity of functionally isolated cardiac contractile structures. This coincides with an inhibitory effect on the cAMP-dependent protein kinase from rat liver. A possible relation with the regulation of troponin I phosphorylation is discussed.
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PMID:Myofibrillar Ca++ activation and heart failure--Ca++ sensitization by the cardiotonic agent APP 201-533. 281 53

Phosphorylation of myofibrillar and sacroplasmic-reticulum (SR) proteins was studied in Langendorff-perfused rabbit hearts subjected to various inotropic interventions. Stimulation of hearts with isoprenaline resulted in the phosphorylation of both troponin I (TnI) and C-protein in myofibrils and phospholamban in SR. Phosphorylation of phospholamban could be reversed by a 15 min perfusion with drug-free buffer, after a 1 minute pulse perfusion with isoprenaline, at which time the mechanical effects of isoprenaline stimulation had also been reversed. However, both TnI and C-protein remained phosphorylated at this time. Moreover, the inhibition of Ca2+ activation of the Mg2+-dependent ATPase (Mg-ATPase) activity associated with myofibrillar phosphorylation persisted in myofibrils prepared from hearts frozen after 15 min of washout of isoprenaline. To assess the contribution of C-protein phosphorylation in the decrease of Ca2+ activation of the myofibrillar Mg-ATPase activity, we reconstituted a regulated actomyosin system in which only C-protein was phosphorylated. In this system, C-protein phosphorylation did not contribute to the decrease in Ca2+ activation of Mg-ATPase activity, indicating that TnI phosphorylation is responsible for the diminished sensitivity of the myofibrils to Ca2+. These observations support the hypothesis that phospholamban phosphorylation plays a more dominant role than TnI or C-protein phosphorylation in the mechanical response of the mammalian heart to beta-adrenergic stimulation.
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PMID:Phosphorylation of C-protein, troponin I and phospholamban in isolated rabbit hearts. 289 34


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