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

---

Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

2-Hydroxycarbazole was shown to induce Ca2+ release from skeletal muscle and cardiac muscle sarcoplasmic reticulum at concentrations between 100-500 microM. This release was blocked by both 1 mM tetracaine and 30 microM ruthenium red which inhibit the ryanodine receptor or by pre-treatment with 10 mM caffeine which depletes the ryanodine receptor-containing Ca2+ stores. This, in addition to the fact that 2-hydroxycarbazole has little effect on Ca2+ ATPase activity, indicates that it activates Ca2+ release through the ryanodine receptor. The apparent EC50 value for release from both skeletal muscle and cardiac muscle sarcoplasmic reticulum was approximately 200 microM and maximal release occurred at 400-500 microM, making it approximately 20 times more potent than caffeine. The dose-dependency in the extent of Ca2+ release induced by 2-hydroxycarbazole was also apparently highly cooperative for both preparations. That 2-hydroxycarbazole was able to mobilize Ca2+ from non-muscle cell microsomes and in intact TM4 cells (which contain ryanodine receptors), makes this compound a more potent and commercially available alternative to caffeine in studying the role of this intracellular Ca2+ channel in a variety of systems.
...
PMID:2-Hydroxycarbazole induces Ca2+ release from sarcoplasmic reticulum by activating the ryanodine receptor. 975 26

The factors regulating Ca2+ transport by isolated sarcoplasmic reticulum (SR) vesicles have been studied using the fluorescent indicator Fluo-3 to monitor extravesicular free [Ca2+]. ATP, in the presence of 5 mM oxalate, which clamps intravesicular [Ca2+] at approximately 10 microM, induced a rapid decline in Fluo-3 fluorescence to reach a limiting steady state level. This corresponds to a residual medium [Ca2+] of 100 to 200 nM, and has been defined as [Ca2+]lim, whilst thermodynamic considerations predict a level of less than 1 nM. This value is similar to that measured in intact muscle with Ca2+ fluophores, where it is presumed that sarcoplasmic free [Ca2+] is a balance between pump and leaks. Fluorescence of Fluo-3 at [Ca2+]lim was decreased 70% to 80% by histidine, imidazole and cysteine. The K0.5 value for histidine was 3 mM, suggesting that residual [Ca2+]lim fluorescence is due to Zn2+. The level of Zn2+ in preparations of SR vesicles, measured by atomic absorption, was 0.47+/-0.04 nmol/mg, corresponding to 0.1 mol per mol Ca-ATPase. This is in agreement with findings of Papp et al. (Arch. Biochem. Biophys., 243 (1985) 254-263). Histidine, 20 mM, included in the buffer, gave a corrected value for [Ca2+]lim of 49+/-1.8 nM, which is still higher than predicted on thermodynamic grounds. A possible 'pump/leak' mechanism was tested by the effects of varying active Ca2+ transport 1 to 2 orders with temperature and pH. [Ca2+]lim remained relatively constant under these conditions. Alternate substrates acetyl phosphate and p-NPP gave similar [Ca2+]lim levels even though the latter substrate supported transport 500-fold slower than with ATP. In fact, [Ca2+]lim was lower with 10 mM p-NPP than with 5 mM ATP. The magnitude of passive efflux from Ca-oxalate loaded SR during the steady state of [Ca2+]lim was estimated by the unidirectional flux of 45Ca2+, and directly, following depletion of ATP, by measuring release of 40Ca2+, and was 0.02% of Vmax. Constant infusion of CaCl2 at [Ca2+]lim resulted in a new steady state, in which active transport into SR vesicles balances the infusion rate. Varying infusion rates allows determination of [Ca2+]-dependence of transport in the absence of chelating agents. Parameters of non-linear regression were Vmax=853 nmol/min per mg, K0.5(Ca)=279 nM, and nH(Ca)=1.89. Since conditions employed in this study are similar to those in the sarcoplasm of relaxed muscle, it is suggested that histidine, added to media in studies of intracellular Ca2+ transients, and in the relaxed state, will minimise contribution of Zn2+ to fluophore fluorescence, since it occurs at levels predicted in this study to cause significant overestimation of cytoplasmic free [Ca2+] in the relaxed state. Similar precautions may apply to non-muscle cells as well. This study also suggests that [Ca2+]lim in the resting state is a characteristic feature of Ca2+ pump function, rather than a balance between active transport and passive leakage pathways.
...
PMID:Regulation of Ca2+ transport by sarcoplasmic reticulum Ca2+-ATPase at limiting [Ca2+]. 1020 10

The actin-based motor protein myosin II plays a critical role in many cellular processes in both muscle and non-muscle cells. Targeted disruption of the Dictyostelium regulatory light chain (RLC) caused defects in cytokinesis and multicellular morphogenesis. In contrast, a myosin heavy chain mutant lacking the RLC binding site, and therefore bound RLC, showed normal cytokinesis and development. One interpretation of these apparently contradictory results is that the phenotypic defects in the RLC null mutant results from mislocalization of myosin caused by aggregation of RLC null myosin. To distinguish this from the alternative explanation that the RLC can directly influence myosin activity, we expressed three RLC point mutations (E12T, G18K and N94A) in a Dictyostelium RLC null mutant. The position of these mutations corresponds to the position of mutations that have been shown to result in familial hypertrophic cardiomyopathy in humans. Analysis of purified Dictyostelium myosin showed that while these mutations did not affect binding of the RLC to the MHC, its phosphorylation by myosin light chain kinase or regulation of its activity by phosphorylation, they resulted in decreased myosin function. All three mutants showed impaired cytokinesis in suspension, and one produced defective fruiting bodies with short stalks and decreased spore formation. The abnormal myosin localization seen in the RLC null mutant was restored to wild-type localization by expression of all three RLC mutants. Although two of the mutant myosins had wild-type actin-activated ATPase, they produced in vitro motility rates half that of wild type. N94A myosin showed a fivefold decrease in actin-ATPase and a similar decrease in the rate at which it moved actin in vitro. These results indicate that the RLC can play a direct role in determining the force transmission and kinetic properties of myosin.
...
PMID:Regulatory light chain mutations affect myosin motor function and kinetics. 1021 54

The high abundance of caldesmon in smooth muscle and its ability to inhibit actomyosin ATPase activity have led to the hypothesis that caldesmon modulates contractile activity. It has also been proposed, however, that caldesmon acts as a structural protein in muscle and non-muscle cells. We have determined the caldesmon content of mammalian cardiac muscle and have found that caldesmon is 200-fold less abundant in cardiac muscle than it is in gizzard smooth muscle. This finding argues against a role for caldesmon in the modulation of cardiac contractility.
...
PMID:Comparison of the caldesmon content of cardiac and smooth muscle. 1042 39

To test for a role of the calcineurin-NFAT (nuclear factor of activated T cells) pathway in the regulation of fiber type-specific gene expression, slow and fast muscle-specific promoters were examined in C2C12 myotubes and in slow and fast muscle in the presence of calcineurin or NFAT2 expression plasmids. Overexpression of active calcineurin in myotubes induced both fast and slow muscle-specific promoters but not non-muscle-specific reporters. Overexpression of NFAT2 in myotubes did not activate muscle-specific promoters, although it strongly activated an NFAT reporter. Thus overexpression of active calcineurin activates transcription of muscle-specific promoters in vitro but likely not via the NFAT2 transcription factor. Slow myosin light chain 2 (MLC2) and fast sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA1) reporter genes injected into rat soleus (slow) and extensor digitorum longus (EDL) (fast) muscles were not activated by coinjection of activated calcineurin or NFAT2 expression plasmids. However, an NFAT reporter was strongly activated by overexpression of NFAT2 in both muscle types. Calcineurin and NFAT protein expression and binding activity to NFAT oligonucleotides were different in slow vs. fast muscle. Taken together, these results indicate that neither calcineurin nor NFAT appear to have dominant roles in the induction and/or maintenance of slow or fast fiber type in adult skeletal muscle. Furthermore, different pathways may be involved in muscle-specific gene expression in vitro vs. in vivo.
...
PMID:The calcineurin-NFAT pathway and muscle fiber-type gene expression. 1100 71

Caldesmon and calponin are two actin- and calmodulin-binding proteins involved in the 'actin-linked' regulation of smooth muscle and non-muscle Mg(2+)-actin-activated myosin II ATPase activity. In the present report we show that caldesmon and calponin are present in the post-synaptic side of symmetric synapses and accumulate in the post-synaptic densities of asymmetric synapses. Caldesmon- and calponin-immunoreactivities are also observed at the plasma membrane of the hippocampal neurones. Finally, while caldesmon seems strictly distributed to neurones, acidic calponin is present in both neurones and astrocytes.
...
PMID:Subcellular distribution of calponin and caldesmon in rat hippocampus. 1113 39

Light chain phosphorylation is the key event that regulates smooth and non-muscle myosin II ATPase activity. Here we show that both heads of smooth muscle heavy meromyosin (HMM) bind tightly to actin in the absence of nucleotide, irrespective of the state of light chain phosphorylation. In striking contrast, only one of the two heads of unphosphorylated HMM binds to actin in the presence of ADP, and the heads have different affinities for ADP. This asymmetry suggests that phosphorylation alters the mechanical coupling between the heads of HMM. A model that incorporates strain between the two heads is proposed to explain the data, which have implications for how one head of a motor protein can gate the response of the other.
...
PMID:ADP binding induces an asymmetry between the heads of unphosphorylated myosin. 1130 26

A protein with adenosine triphosphatase activity was isolated from bovine adrenal medulla and subsequently purified by ammonium sulfate precipitation and agarose gel filtration using a discontinuous two-buffer system. Characterization of this protein by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate, by assay of the activity of Ca2+, K(+)-EDTA and Mg2+ dependent adenosine triphosphatases by amino acid analysis and by electron microscopy has shown that the adrenal medullary myosin closely resembles those myosins isolated from muscle and other non-muscle cells. The possible roles of myosin in the adrenal medulla are discussed.
...
PMID:Isolation and characterization of myosin from the adrenal medulla. 1137 Feb 41

Intracellular Ca(2+)-transport ATPases exert a pivotal role in the endoplasmic reticulum and in the compartments of the cellular secretory pathway by maintaining a sufficiently high lumenal Ca(2+) (and Mn(2+)) concentration in these compartments required for an impressive number of vastly different cell functions. At the same time this lumenal Ca(2+) represents a store of releasable activator Ca(2+) controlling an equally impressive number of cytosolic functions. This review mainly focuses on the different Ca(2+)-transport ATPases found in the intracellular compartments of mainly animal non-muscle cells: the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) pumps. Although it is not our intention to treat the ATPases of the specialized sarcoplasmic reticulum in depth, we can hardly ignore the SERCA1 pump of fast-twitch skeletal muscle since its structure and function is by far the best understood and it can serve as a guide to understand the other members of the family. In a second part of this review we describe the relatively novel family of secretory pathway Ca(2+)/Mn(2+) ATPases (SPCA), which in eukaryotic cells are primarily found in the Golgi compartment.
...
PMID:Molecular physiology of the SERCA and SPCA pumps. 1254 90

Besides driving contraction of various types of muscle tissue, conventional (class II) myosins serve essential cellular functions and are ubiquitously expressed in eukaryotic cells. Three different isoforms in the human myosin complement have been identified as non-muscle class II myosins. Here we report the kinetic characterization of a human non-muscle myosin IIB subfragment-1 construct produced in the baculovirus expression system. Transient kinetic data show that most steps of the actomyosin ATPase cycle are slowed down compared with other class II myosins. The ADP affinity of subfragment-1 is unusually high even in the presence of actin filaments, and the rate of ADP release is close to the steady-state ATPase rate. Thus, non-muscle myosin IIB subfragment-1 spends a significantly higher proportion of its kinetic cycle strongly attached to actin than do the muscle myosins. This feature is even more pronounced at slightly elevated ADP levels, and it may be important in carrying out the cellular functions of this isoform working in small filamentous assemblies.
...
PMID:Kinetic mechanism of non-muscle myosin IIB: functional adaptations for tension generation and maintenance. 1270 89


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---