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)

Chronic excitation, at 2 Hz for 6-7 weeks, of the predominantly fast-twitch canine latissimus dorsi muscle promoted the expression of phospholamban, a protein found in sarcoplasmic reticulum (SR) from slow-twitch and cardiac muscle but not in fast-twitch muscle. At the same time that phospholamban was expressed, there was a switch from the fast-twitch (SERCA1) to the slow-twitch (SERCA2a) Ca(2+)-ATPase isoform. Antibodies against Ca(2+)-ATPase (SERCA2a) and phospholamban were used to assess the relative amounts of the slow-twitch/cardiac isoform of the Ca(2+)-ATPase and phospholamban, which were found to be virtually the same in SR vesicles from the slow-twitch muscle, vastus intermedius; cardiac muscle; and the chronically stimulated fast-twitch muscle, latissimus dorsi. The phospholamban monoclonal antibody 2D12 was added to SR vesicles to evaluate the regulatory effect of phospholamban on calcium uptake. The antibody produced a strong stimulation of calcium uptake into cardiac SR vesicles, by increasing the apparent affinity of the Ca2+ pump for calcium by 2.8-fold. In the SR from the conditioned latissimus dorsi, however, the phospholamban antibody produced only a marginal effect on Ca2+ pump calcium affinity. These different effects of phospholamban on calcium uptake suggest that phospholamban is not tightly coupled to the Ca(2+)-ATPase in SR vesicles from slow-twitch muscles and that phospholamban may have some other function in slow-twitch and chronically stimulated fast-twitch muscle.
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PMID:Phospholamban expressed in slow-twitch and chronically stimulated fast-twitch muscles minimally affects calcium affinity of sarcoplasmic reticulum Ca(2+)-ATPase. 146 16

Rat seminal vesicles and the lateral prostate secrete a glycoprotein designated as SVS II in an androgen-dependent manner. SVS II, which has a M(r) of 49,000 and a pI of 10.5, is an actin-binding protein. G- and F-actins cosediment with SVS II at a ratio of 2:1 (actin:SVS II). SVS II affects the kinetics of actin polymerization in the same way as do barbed end capping proteins. Interaction with actin is specific for the skeletal and cardiac muscle isoforms and there is no corresponding interaction with cytoplasmic actins. The binding site is close to the C-terminus of actin. Monospecific polyclonal antibodies directed against the N-terminus of actin cross-react with SVS II, but there is no cross-reaction by a monoclonal antibody directed against a C-terminal epitope on actin. Recent sequence analysis of SVS II shows a sequence of about 14 residues that is repeated 13 times between residues 86 and 298. The consensus sequence based on these repeats is homologous to residues 10 to 25 of actin; this may account for the immunological cross-reactivity. Like actin, SVS II binds and inhibits the activity of DNase I, but SVS II has no effect on the ATPase activity of myosin subfragment 1. Thus, SVS II is an actin-binding protein which retains some properties of actin itself.
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PMID:SVS II--an androgen-dependent actin-binding glycoprotein in rat semen. 151 6

Toxicosis by monensin, a Na(+)-selective ionophore, induces skeletal and cardiac muscle necrosis. Cultured neonatal rat cardiac myocytes were killed by monensin (greater than 0.2 micrograms/ml) beginning at 30 min and completing by 60-90 min. Other cultured cell types presumably lacking excitable membranes were not killed by monensin under these conditions. Cardiac myocytes were also killed by nigericin and nonactin (monovalent cation-carrying ionophores with low ion selectivity), but not by valinomycin, which has a high selectivity for K+. Monensin-induced killing was associated with formation of blebs in cell membranes and subsequent swelling of the cells during the early phases of killing, whereas surface membranes of cells permeabilized to trypan blue dye contained discrete small holes visible by scanning electron microscopy. Monensin-induced killing occurred at extracellular Na+ concentrations greater than or equal to 10 mM, but not when Li+, K+, Cs+, Rb+, or choline ions replaced Na+ at concentrations up to 0.15 M. Killing was prevented at extracellular pH values less than or equal to 6.4 and was enhanced by ouabain, an inhibitor of Na+/K(+)-ATPase-mediated Na+ transport. Several characteristics of monensin-induced cardiac myocyte killing were similar to those observed during killing induced by the Ca(2+)-carrying ionophore, A23187 plus Ca2+, including a requirement for extracellular Ca2+ concentrations greater than 0.5 mM, inhibition by Mn2+ and Ni2+, and an associated stimulation of arachidonic acid release. The cell killing characteristics are consistent with a monensin-induced Na+ influx which admits toxic levels of extracellular Ca2+ to the cytoplasm of cells with excitable membranes, possibly via Na+/Ca2+ antiporter protein(s).
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PMID:Sodium- and calcium-dependent steps in the mechanism of neonatal rat cardiac myocyte killing by ionophores. I. The sodium-carrying ionophore, monensin. 152 51

Fast skeletal and cardiac troponin C (TnC) contain two high affinity Ca2+/Mg2+ binding sites within the C-terminal domain that are thought to be important for association of TnC with the troponin complex of the thin filament. To test directly the function of these high affinity sites in cardiac TnC they were systematically altered by mutagenesis to generate proteins with a single inactive site III or IV (CBM-III and CBM-IV, respectively), or with both sites III and IV inactive (CBM-III-IV). Equilibrium dialysis indicated that the mutated sites did not bind Ca2+ at pCa 4. Both CBM-III and CBM-IV were similar to the wild type protein in their ability to regulate Ca(2+)-dependent contraction in slow skeletal muscle fibers, and Ca(2+)-dependent ATPase activity in fast skeletal and cardiac muscle myofibrils. The mutant CBM-III-IV is capable of regulating contraction in permeabilized slow muscle fibers but only if the fibers are maintained in a contraction solution containing a high concentration of the mutant protein. CBM-III-IV also regulates myofibril ATPase activity in fast skeletal and cardiac myofibrils but only at concentrations 10-100-fold greater than the normal protein. The pCa50 and Hill coefficient values for Ca(2+)-dependent activation of fast skeletal muscle myofibril ATPase activity by the normal protein and all three mutants are essentially the same. Competition between active and inactive forms of cardiac and slow TnC in a functional assay demonstrates that mutation of both sites III and IV greatly reduces the affinity of cardiac and slow TnC for its functionally relevant binding site in the myofibrils. The data indicate that although neither high affinity site is absolutely essential for regulation of muscle contraction in vitro, at least one active C-terminal site is required for tight association of cardiac troponin C with myofibrils. This requirement can be satisfied by either site III or IV.
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PMID:Mutation of the high affinity calcium binding sites in cardiac troponin C. 153 Sep 38

To examine the signals regulating cardiac growth and molecular structure of subcellular organelles, cardiac hypertrophy was induced in rats by constriction of the abdominal aorta for 12-13 wk or by treatment with a carnitine palmitoyltransferase I inhibitor, etomoxir (12-15 mg/kg body wt) for 12-13 wk. In contrast to pressure overload, etomoxir redistributed the myosin isozyme population from V3 to V1 and increased the sarcoplasmic reticulum (SR) Ca(2+)-stimulated ATPase activity. When rats with pressure-overloaded hearts were treated with etomoxir, the cardiac hypertrophy was increased whereas the shift in myosin isozymes from V1 to V3 was prevented and the depression in SR Ca(2+)-stimulated ATPase activity was reversed. Plasma thyroid hormone and insulin concentrations were not altered but triglyceride concentrations were reduced in etomoxir-treated rats with pressure overload. The data demonstrate a dissociation between cardiac muscle growth and changes in subcellular organelles and indicate that a shift in myocardial substrate utilization may represent an important signal for molecular remodeling of the heart.
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PMID:Modification of subcellular organelles in pressure-overloaded heart by etomoxir, a carnitine palmitoyltransferase I inhibitor. 153 68

The formation of palmitoylcarnitine is catalyzed by carnitine palmitoyl-transferase (CPT-I) and this catalysis is the first committed step in beta-oxidation. The malonyl-CoA-inhibited isoform appears to be distinct from latent (CPT-II) activity, which is localized to the matrix side of the mitochondrial inner membrane. Sarcoplasmic reticulum from canine cardiac muscle was fractionated on a discontinuous sucrose density gradient into three major bands, all of which contained Ca(2+)-ATPase activity. Only the fraction that banded at a concentration of 38% surcrose was slightly contaminated by mitochondria. Peroxisomal uricase was low or absent in fractionated SR. All sarcoplasmic reticulum fractions contained malonyl-CoA-sensitive medium- (COT) and long-chain (CPT) carnitine acyltransferase activities. CPT activity decreased in sarcoplasmic reticulum when Triton X-100 was present. Carnitine acyltransferase activities were inactivated by preincubating the sarcoplasmic reticulum with the sulfhydryl reagent, 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB). In contrast, mitochondrial CPT-II activity was stable in the presence of DTNB and activated by Triton X-100. Western blots of mitochondria and sarcoplasmic reticulum fractions showed that the mitochondrial fractions reacted with antibody to mitochondrial CPT-II but not with SR protein when both were added at comparable specific activities. The data suggest that cardiac SR contains a unique malonyl-CoA-sensitive isoform of CPT, and that synthesis of acylcarnitine may occur in the microenvironment of Ca2+ transport, where the extent of production of acylcarnitine is controlled by cardiac acetyl-CoA carboxylase activity.
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PMID:Evidence for malonyl-CoA-sensitive carnitine acyl-CoA transferase activity in sarcoplasmic reticulum of canine heart. 162 48

Both contraction and relaxation times are prolonged in cardiac muscle of senescent animals. This is in part explained by an alteration of excitation-contraction coupling due to an increased duration of the action potential, reduced biosynthesis of the Ca(2+)-stimulated ATPase pump of sarcoplasmic reticulum, and prevalence of the V3 isoform of myosin with slow ATPase activity. The response to catecholamine decreases with aging because of a defective transmission of alpha and beta adrenergic stimulation mediated respectively by phosphoinositide hydrolysis and adenylate cyclase. Cardiac energetics is also impaired in the aged myocardium, since ATP and creatine phosphate levels are reduced by about 20%. This reduction seems in part the consequence of defective mitochondrial function, especially in fatty acid oxidation and ATP translocation to the cytoplasm. In this paper we have discussed the possibility that oxygen free radicals may be a cause of myocardial senescence, by damaging the nuclear and mitochondrial genomes as well as membranes and other cellular components.
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PMID:Biochemical correlates with myocardial aging. 164 41

One of the fundamental properties of cardiac muscle is the increase in force generated and work performed with a rise in the resting length of the tissue. There are data to indicate that length-dependent responses of electromechanical coupling and calcium binding by troponin are part of the basis for the pressure-volume relation in the heart. In this study, the contribution of changes in the functional properties of the contractile proteins independent of modification in electromechanical coupling has been examined. Isolated working hearts containing either a mixture of myosin heavy chain (MHC) isozymes (alpha[fast] and beta [slow]) or exclusively the fast MHC have been subjected to left atrial filling pressures (LAPs) between 5 and 20 cm H2O. After 40 minutes at a given LAP, the heart was quickly frozen. The relative activities of calcium- and actin-activated ATPase of V1 and V3 myosin, containing alpha- and beta-MHC, were measured in cryostatic sections of the heart by quantitative histochemistry under conditions for which the concentration of calcium would not be limiting. In hearts containing both isozymes of myosin, the relative enzymatic activity of each isozyme of myosin varied with LAP. At low LAP, V1 was primarily responsible for the enzymatic activity, but as LAP increased the relative contribution of V1 decreased and that of V3 increased. The change in the calcium- and actin-activated activities of the enzyme with change in LAP occurred within 5 minutes and was reversible. In spite of the apparent substitution of enzymatic activity of V3 for V1, total myosin ATPase activity did not decline, but instead remained constant.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effect of left atrial filling pressure on the activity of specific myosin isozymes in rat heart. 164 32

The purpose of this study was to determine if selected biochemical parameters representing the contractile and calcium regulating systems of cardiac muscle scaled among mammals having inherently different resting heart rates (RHR). Eight mammalian species with RHR ranging from 51 to 475 beats per minute (bpm) were studied. The oxidative capacity of the myocardium is highly correlated with the RHR. The hypothesis of the present study was that the capacities of the energy utilizing processes of contraction and calcium regulation would also be correlated to the functional demand imposed on the muscle as represented by the RHR. Myosin (M) and myofibrillar (MF) ATPase activities, myosin isoenzyme distribution and sarcoplasmic reticulum (SR) ATPase activity were determined. Animals with RHR above 300 bpm express V1 myosin while animals with lower RHR express primarily V3. M and MF ATPase activities correlated with RHR, but the major difference in activities occurred at the 'threshold' RHR of about 300 bpm at which the switch from V3 to V1 appears to occur. SR ATPase activity per mg of microsomal protein was for the most part constant among different mammals, but the SR ATPase activity per g of heart tissue was significantly correlated with RHR as slower beating hearts tended to yield less SR protein per unit mass. We conclude that both the contractile and calcium regulating systems are scaled to the functional parameter of RHR among different mammals. The contractile system uses a slow myosin ATPase isoform at low resting heart rates whereas above the postulated threshold RHR of about 300 bpm a switch in gene expression to a fast myosin ATPase isoform occurs.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Contractile and calcium regulating capacities of myocardia of different sized mammals scale with resting heart rate. 165 10

Contraction in cardiac muscle is activated by a combination of Ca influx via sarcolemmal Ca channels and release of Ca from the sarcoplasmic reticulum (SR). The release of Ca from the SR appears to be triggered by Ca influx via a Ca-induced Ca-release mechanism. The amount of Ca influx and Ca released from the SR vary with conditions and with different cardiac muscle preparations. In contrast to the Ca-induced Ca-release process in cardiac muscle, excitation-contraction coupling in skeletal muscle appears to be via a more direct coupling between sarcolemmal voltage sensors and the Ca release (sometimes referred to as depolarization-induced Ca-release). During cardiac relaxation Ca is removed from the cytoplasm by the SR Ca-pump and the sarcolemmal Na/Ca exchange (with the former being somewhat more dominant). Ca extrusion from the cell during both relaxation and diastole is predominantly via Na/Ca exchange, with the sarcolemmal Ca ATPase pump contributing very little. Thus, sarcolemmal Na/Ca exchange appears to be critically involved in the overall regulation of cardiac cellular Ca content.
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PMID:Ca regulation in cardiac muscle. 166 31


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