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)

Phospholamban, the putative regulatory proteolipid of the Ca2+/Mg2+ ATPase in cardiac sarcoplasmic reticulum, was selectively phosphorylated by a Ca2+/calmodulin (CaM)-dependent protein kinase associated with a cardiac membrane preparation. This kinase also catalyzed the phosphorylation of two exogenous proteins known to be phosphorylated by the multifunctional Ca2+/CaM-dependent protein kinase II (Ca2+/CaM-kinase II), i.e., smooth muscle myosin light chains and glycogen synthase a. The latter protein was phosphorylated at sites previously shown to be phosphorylated by the purified multifunctional Ca2+/CaM-kinase II from liver and brain. The membrane-bound kinase did not phosphorylate phosphorylase b or cardiac myosin light chains, although these proteins were phosphorylated by appropriate, specific calmodulin-dependent protein kinases added exogenously. In addition to phospholamban, several other membrane-associated proteins were phosphorylated in a calmodulin-dependent manner. The principal one exhibited a Mr of approximately 56,000, a value similar to that of the major protein (57,000) in a partially purified preparation of Ca2+/CaM-kinase II from the soluble fraction of canine heart that was autophosphorylated in a calmodulin-dependent manner. These data indicate that the membrane-bound, calmodulin-dependent protein kinase that phosphorylates phospholamban in cardiac membranes is not a specific calmodulin-dependent kinase, but resembles the multifunctional Ca2+/CaM-kinase II. Our data indicate that this kinase may be present in both the particulate and soluble fractions of canine heart.
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PMID:Identification of membrane-bound calcium, calmodulin-dependent protein kinase II in canine heart. 295 8

Treatment of cardiac sarcoplasmic reticulum with the crosslinking reagent dithiobis (succinimidyl propionate) in the presence of 125I-calmodulin, resulted in the formation of a 40,000-dalton affinity labeled component, consisting of a 1:1, phospholamban: 125I-calmodulin complex. In parallel experiments, sarcoplasmic reticulum was phosphorylated in the presence of calmodulin and [gamma-32P]ATP, and then treated with the crosslinking reagent to produce an affinity labeled component consisting of a 1:1, calmodulin: 32P-phospholamban complex. These experiments permitted determination of the amount of 125I and 32P incorporated into the 40,000-dalton complexes, as well as the amount of 32P incorporated into the 23,000-dalton form of phospholamban. If 1 mol of Ca2+-dependent ATPase phosphoprotein represents 1 mol of 100,000-dalton Ca2+-dependent ATPase monomer, then there are 4.88 +/- 1.33 mol Ca2+-dependent ATPase/mol of phospholamban. If there are 2 mol of Ca2+-dependent ATPase phosphoprotein/mol of 100,000-dalton Ca2+-dependent ATPase monomer, then there are 9.76 +/- 2.66 mol Ca2+-dependent ATPase/mol phospholamban.
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PMID:Phospholamban stoichiometry in canine cardiac muscle sarcoplasmic reticulum. 296 Sep 9

Isolated cardiac Ca,Mg-dependent ATPase of the sarcoplasmic reticulum and purified phospholamban, a proteolipid involved in the regulation of the calcium transport systems of the heart muscle, were reconstituted into soybean lecithin liposomes. Whereas the enzymatic activity of the CaATPase in the obtained liposomes was unaffected as well as by unphosphorylated and cAMP-dependent phosphorylated phospholamban, the capacity of oxalate-supported calcium uptake was lowered in the presence of phospholamban. The proteolipid is discussed not as a regulatory protein of the enzyme but as a mediator of the calcium storage in the lumen of the liposomes or sarcoplasmic reticulum network.
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PMID:Reconstitution of phospholamban--an approach to its function. 296 26

Phospholamban, a phosphorylatable protein of the cardiac sarcoplasmic reticulum, has been estimated by a semi-quantitative immunoassay. It can be determined in purified membrane preparations as well as in crude fractions of cardiac muscle membranes, regardless of the phosphorylation state of the phosphoprotein. The content of phospholamban in mammalian heart muscle membrane vesicles correlates with the activity of the calcium/magnesium-dependent ATPase with the exception of the oxalate-loaded membrane preparations. This observation indicates that phospholamban and the calcium transporting enzyme are localized at different sites in cardiac sarcoplasmic reticulum.
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PMID:An enzyme immunoassay for phospholamban. 296 99

The activity of calcium pumping adenosine triphosphatase (Ca2+-ATPase) in cardiac sarcoplasmic reticulum plays a pivotal role in myocardiac contraction-relaxation. The Ca2+-ATPase activity is controlled by phosphorylation and dephosphorylation of a sarcoplasmic reticulum protein "phospholamban" in response to neurotransmitters and drugs. To clarify the role of Ca2+-ATPase in the development of cardiac rigor mortis, we examined the changes of cardiac rigidity and cardiac sarcoplasmic reticulum Ca2+-ATPase activity up to 5 h after the decapitation of rats. Fifteen minutes after decapitation, the rats showed a cardiac rigidity on left ventricles. After 30 min, rigidity was obvious over the whole heart. After 1 h, the rigidity reached a high degree which was maintained for the rest of the observation period. On the other hand, the Ca2+-ATPase activity controlled by phosphorylation and dephosphorylation of phospholamban did not change for the whole observation period (5 h). Another Ca2+-ATPase activity representing the total amount of Ca2+-ATPase in sarcoplasmic reticulum gradually decreased. The data suggest that no significant phosphorylation or dephosphorylation of phospholamban occurs for a short time, at least for 5 h, after death and that the Ca2+-ATPase tends to relax the myocardium against the development of cardiac rigor mortis.
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PMID:Postmortem changes in the level of calcium pumping adenosine triphosphatase in rat heart sarcoplasmic reticulum. 297 25

The gel-overlay technique with 125I-labelled calmodulin allowed the detection of several calmodulin-binding proteins of Mr 280 000, 150 000, 97 000, 56 000, 35 000 and 24 000 in canine cardiac sarcoplasmic reticulum. Only two calmodulin-binding proteins could be identified unambiguously. Among them, the 97 000-Mr protein that undergoes phosphorylation in the presence of Ca2+ and calmodulin, is likely to be glycogen phosphorylase. In contrast, the (Ca2+ + Mg2+)-activated ATPase did not appear to bind calmodulin under our experimental conditions. The second known calmodulin target is dephosphophospholamban, which migrates with an apparent Mr of 24 000. The dimeric as well as the monomeric form of phospholamban was found to bind calmodulin. Phospholamban shifts the apparent Kd of erythrocyte (Ca2+ + Mg2+)-activated ATPase for calmodulin, suggesting thus a tight binding of calmodulin to the proteolipid. Interestingly enough, phospholamban phosphorylation by either the catalytic subunit of cyclic AMP-dependent protein kinase or the Ca2+/calmodulin-dependent phospholamban kinase was found to inhibit calmodulin binding.
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PMID:Cardiac sarcoplasmic-reticulum calmodulin-binding proteins. Modulation of calmodulin binding to phospholamban by phosphorylation. 298 48

Physiologic studies suggest that the myocardium from fetal and newborn sheep functions at a higher contractile state with decreased contractile reserve when compared to the myocardium of adult sheep. To investigate the role of Ca2+ transport by the sarcoplasmic reticulum (SR) in this phenomenon, we studied functional properties and protein composition of cardiac SR vesicles isolated from fetal and maternal sheep. Active accumulation of Ca2+ and the density of the Ca2+ pump protein were decreased 60% (p less than 0.01) in fetal SR vesicles; however Ca2+-dependent ATPase activity was decreased only 30% (p less than 0.01). This decreased difference in Ca2+-dependent ATPase activities was accounted for by the higher turnover number measured for the Ca2+ pump of fetal SR vesicles (1.6-fold increased, p less than 0.01). Ryanodine, an alkaloid which blocks Ca2+ efflux from cardiac SR vesicles, stimulated Ca2+ uptake more effectively in fetal SR vesicles, suggesting that these vesicles had a higher passive Ca2+ permeability during conditions of active Ca2+ transport. Protein compositional studies showed that the content of phospholamban was decreased in fetal SR vesicles and was correlated with the decrease in the density of Ca2+ pumps. In contrast, the content of calsequestrin and the density of [3H]nitrendipine-binding sites were increased approximately 2-fold in fetal SR vesicles. These functional and compositional differences between SR vesicles isolated from fetal and maternal sheep may indicate that there is relatively more junctional SR in fetal hearts. Since the SR regulates muscle contraction by modulating intracellular Ca2+ concentration, it is possible that developmental alterations in cardiac SR may contribute to the decreased myocardial contractile reserve noted in fetal sheep.
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PMID:Developmental changes in cardiac sarcoplasmic reticulum in sheep. 302 68

The composition and function of fetal and mature sheep cardiac sarcoplasmic reticulum membranes were investigated. Phospholamban, a major phosphoprotein in the mature sarcoplasmic reticulum membranes, was present in early stages of cardiac myogenesis. This fetal form of phospholamban was phosphorylated by cAMP-dependent protein kinase but not in the presence of Ca2+ and calmodulin. Ca2+ uptake and Ca2+-dependent ATPase activity were low in fetal sarcoplasmic reticulum compared with the adult controls, although the apparent affinities for Ca2+ were similar. Sarcoplasmic reticulum vesicles isolated at all developmental stages had very low levels of plasma membrane (as determined by Na+-K+-ATPase and Na+-Ca2+ exchanger activities) and mitochondrial contamination. Sarcoplasmic reticulum Ca2+ uptake and Ca2+-dependent ATPase activities were not affected by micromolar concentrations of vanadate, and the accumulated Ca2+ could not be released by the addition of NaCl. The amount of both the 110- and 55-kDa protein bands, identified with specific antibodies as Ca2+-ATPase and calsequestrin, respectively, was low in early stages of cardiac myogenesis. Age-related differences in the Ca2+ transport properties of cardiac sarcoplasmic reticulum and in the amount of the Ca2+-ATPase and calsequestrin may explain alterations in the regulation of intracellular Ca2+ concentrations in the fetal heart. This may contribute to the developmental changes in myocardial function.
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PMID:Differentiation of sarcoplasmic reticulum during cardiac myogenesis. 302 62

Phosphorylation of cardiac sarcoplasmic reticulum membrane vesicles by exogenous c-AMP and c-AMP-dependent protein kinase stimulates calcium uptake and Ca2+-dependent ATP hydrolysis by 40-50% and results in the incorporation of 32P into a 22-KDa protein, phospholamban. Treatment of the membrane with DOC (0.0002% or 5 X 10(-6) M) solubilizes phospholamban from the membrane and induces a 90% inhibition of basal calcium uptake. This inhibition cannot be attributed to an alteration in vesicle integrity or membrane permeability. The (Ca2+ + Mg2+)-ATPase remains associated with the membrane fraction and exhibits optimal levels of Ca2+-stimulated ATP hydrolysis. Phosphorylation prior to DOC treatment allows retention of the phospholamban in the membrane, concomitant with maintenance of the calcium transport activity. The results presented suggest that phospholamban is involved in the maintenance of basal calcium transport function in cardiac sarcoplasmic reticulum and that its phosphorylation stimulates Ca2+ transport.
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PMID:Phospholamban involvement in the maintenance of basal calcium transport in cardiac sarcoplasmic reticulum. 303 32

Cardiac sarcolemma was purified from canine ventricles. Enrichment of the sarcolemmal membranes was demonstrated by the high (Na+ + K+)-ATPase activity of 28.0 +/- 1.5 mumol Pi/mg protein per h and the high concentration of muscarinic receptors with the Bmax of 8.2 +/- 2.5 pmol/mg protein as determined by [3H]QNB binding. The purified sarcolemma also contains significant levels of a membrane-bound Ca2+ and phospholipid-dependent protein kinase (protein kinase C). To elucidate the protein kinase C activity in sarcolemma, a prior incubation of the membranes with EGTA and Triton X-100 was necessary. The specific activity of protein kinase C was found to be 131.4 pmol Pi/mg per min, in the presence of 6.25 micrograms phosphatidylserine and 0.5 mM CaCl2. Treatment of sarcolemma with 12-O-tetradecanoylphorbol 13-acetate (TPA) and phorbol 12,13-dibutyrate (PBu2) resulted in a concentration-dependent activation of protein kinase C activity. The effect of TPA and PBu2 on protein kinase C in sarcolemma was independent of exogenous Ca2+ and phosphatidylserine. Polymyxin B inhibited phorbol-ester-induced activation of protein kinase C activity. The distribution of protein kinase C in the cytosolic fraction was also examined. The specific activity of the kinase in the cytosolic fraction was 59.7 pmol Pi/mg per min. However, the total protein kinase C activity in the cytosol was 213500 pmol Pi/min, compared to that of 1025 pmol Pi/min in the sarcolemma isolated from approx. 100 g of canine ventricular muscle. Several endogenous proteins in cardiac sarcolemma were phosphorylated in the presence of Ca2+ and phosphatidylserine. The major substrates for protein kinase C were proteins of Mr 94 000, 87 000, 78 000, 51 000, 46 000, 11 500 and 10 000. Most of these substrate proteins have not been identified before. Other proteins of Mr 38 000, 31 000 and 15 000 were markedly phosphorylated in the presence of Ca2+ only. Phosphorylation of phospholamban (Mr 27 000 and 11 000) was also stimulated in the presence of Ca2+ and phosphatidylserine, but the low Mr form of phospholamban was distinct from two other low Mr substrate proteins for protein kinase C. Polymyxin B was more selective in inhibiting the protein kinase C dependent phosphorylation. On the other hand, trifluoperazine selectively inhibited the phosphorylation of phospholamban and Mr 15 000 protein. Although the exact function of this kinase is unknown, based on these observations, we believe that protein kinase C in the cardiac sarcolemma may play an important role in the cell-surface-signal regulated cardiac function.
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PMID:Characterization of the membrane-bound protein kinase C and its substrate proteins in canine cardiac sarcolemma. 308 70


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