Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.11 (AMPK)
 12,425 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Phospholamban is the regulator of the Ca(2+)-ATPase in cardiac sarcoplasmic reticulum (SR). The mechanism of regulation appears to involve inhibition by dephosphorylated phospholamban, and phosphorylation may relieve this inhibition. Fast-twitch skeletal muscle SR does not contain phospholamban, and it is not known whether the Ca(2+)-ATPase isoform from this muscle may be also subject to regulation by phospholamban in a similar manner as the cardiac isoform. To determine this we reconstituted the skeletal isoform of the SR Ca(2+)-ATPase with phospholamban in phosphatidylcholine proteoliposomes. Inclusion of phospholamban was associated with significant inhibition of the initial rates of Ca2+ uptake at pCa 6.0, and phosphorylation of phospholamban by the catalytic subunit of cAMP-dependent protein kinase reversed the inhibitory effects on the Ca2+ pump. Similar effects of phospholamban were also observed using phosphatidylcholine:phosphatidylserine proteoliposomes, in which the Ca2+ pump was activated by the negatively charged phospholipids (24). Regulation of the Ca(2+)-ATPase appeared to involve binding with the hydrophilic portion of phospholamban, as evidenced by cross-linking experiments, using a synthetic peptide that corresponded to amino acids 1-25 of phospholamban. These findings suggest that the fast-twitch isoform of the SR Ca(2+)-ATPase may be also regulated by phospholamban, although this regulator is not expressed in fast-twitch skeletal muscles.
 ...
PMID:Regulation of the skeletal sarcoplasmic reticulum Ca2+ pump by phospholamban in reconstituted phospholipid vesicles. 215 30

Noninsulin-dependent diabetes is associated with a decrease in the activity of sarcolemmal phosphatase 1, but no change in the activities of phosphatase 2A, 2B, or 2C. Also unaffected by diabetes were the activities of protein kinase C, cAMP-dependent protein kinase and calcium-calmodulin protein kinase. Because of the decrease in phosphatase 1 activity, 32P incorporation into sarcolemmal phosphoproteins catalyzed by either intrinsic protein kinases or extrinsic cAMP-dependent protein kinase was elevated in the diabetic. Among the proteins whose phosphorylation was elevated in diabetes was the phospholamban-like protein, which has been implicated in the regulation of ATP-dependent calcium transport. The phosphate-linked increase could be prevented by exposing the membranes to a phosphatase inhibitor and either extrinsic cAMP-dependent protein kinase or alamethicin. In addition to the phosphatase-linked effects, analysis of individual sarcolemmal phosphoproteins by SDS-polyacrylamide gel electrophoresis indicated that diabetes caused a specific elevation in membrane phosphorylation of some proteins (43 kDa and 78 kDa), but a decrease in the phosphorylation state of other phosphoproteins (31 kDa and 49 kDa). The data indicate that membrane phosphorylation is dramatically altered by diabetes. The possibility that this contributes to altered myocardial function is discussed.
 ...
PMID:Defective sarcolemmal phosphorylation associated with noninsulin-dependent diabetes. 215 49

Effects of endotoxin administration on the phosphorylation and dephosphorylation of phospholamban in canine cardiac sarcoplasmic reticulum (SR) were studied. Results obtained 4 h after endotoxin administration show that the Ca2(+)-calmodulin dependent phosphorylation of phospholamban was reduced by 17-25% (P less than 0.05). Kinetic analysis reveals that the Vmax values for Ca2+, for calmodulin, and for ATP for the Ca2(+)-calmodulin dependent phosphorylation were significantly decreased, while the S0.5 values (for Ca2+ and calmodulin) and the Km (for ATP) and Hill coefficients (for Ca2+ and calmodulin) remained unaffected during endotoxic shock. The cAMP-dependent phosphorylation of phospholamban measured in the presence of the exogenously added catalytic subunit of the cAMP-dependent protein kinase remained unaffected. The basal/endogenous (cAMP- and Ca2(+)-independent) phosphorylation of phospholamban was significantly decreased after endotoxin administration. The half-time for the dephosphorylation of phospholamban prephosphorylated in the presence of Ca2+ and calmodulin was shortened by 58% (P less than 0.01) in endotoxin shock. These data indicate that the phosphorylation of phospholamban was inhibited while the dephosphorylation was stimulated in canine cardiac SR during endotoxin shock. Since the phosphorylation and dephosphorylation of phospholamban in cardiac SR plays an important role in the control of myocardial contractility, these findings may have a pathophysiological significance in contributing to the understanding of myocardial dysfunction in endotoxin shock.
 ...
PMID:Impairment in the phosphorylation of canine cardiac sarcoplasmic reticulum following endotoxin administration. 216 86

Acceleration of cardiac relaxation upon beta adrenergic stimulation is due, in part, to enhancement in the rate of Ca2+ sequestration by the sarcoplasmic reticulum (SR) Ca2+ pump resulting from cAMP-mediated phosphorylation of the SR protein phospholamban. Our previous studies have shown that in rat myocardium, beta adrenergic activation of adenylate cyclase and the Ca2+ pump activity of SR decline with aging (Mech. Ageing Dev., 19 (1982) 127-139; 38 (1987) 127-143). In the present study, the effect of aging on phospholamban phosphorylation and consequent changes in SR Ca2+ pump activity were evaluated using cardiac SR from 6 (young adult), 12 (adult) and 28 (aged) months old rats. No age-related differences were observed in the rate or maximum level of phospholamban phosphorylation by exogenous cAMP-dependent protein kinase. The rates of ATP-dependent Ca2+ uptake by SR from young adult and aged rats were stimulated upon phospholamban phosphorylation, the percentage stimulation of Ca2+ uptake at varying Ca2+ concentrations (0.24-11.9 microM) was not diminished with aging. However, the rates of Ca2+ uptake by phosphorylated and unphosphorylated SR were remarkably lower (35-50%) in the aged. Regardless of the age of rats, the stimulatory effect of phosphorylation on Ca2+ uptake by SR was due to increase in Vmax of Ca2+ transport with no appreciable changes in K0.5 for Ca2+. These findings imply that in spite of the age-associated decline in SR Ca2+ pump activity, the ability of phospholamban to undergo cAMP-mediated phosphorylation and the relative responsiveness of the SR Ca2+ pump to phospholamban phosphorylation are not diminished in the aging heart.
 ...
PMID:Effects of aging on phospholamban phosphorylation and calcium transport in rat cardiac sarcoplasmic reticulum. 236 95

Six electrophoretically distinct species of oligomeric phospholamban were identified immunologically following phosphorylation of sarcoplasmic reticulum vesicles by cAMP-dependent protein kinase. The phosphate content of each was determined, confirming that the discrete sequential retardation of phospholamban oligomers was the result of ascending mole ratios of phosphate (P0-P5) per oligomer. These data afford support to the pentameric arrangement of oligomeric phospholamban and offer a means of determining phosphorylation stoichiometry independent of the absolute phospholamban concentration. Detection of the relative concentration of individual species during phosphorylation facilitated the description of a random mechanism of phosphorylation by cAMP-dependent protein kinase. By contrast, dephosphorylation of cAMP-dependent protein kinase phosphorylated phospholamban was shown to exhibit strong positive cooperativity in its reaction mechanism.
 ...
PMID:Immunological detection of phospholamban phosphorylation states facilitates the description of the mechanism of phosphorylation and dephosphorylation. 237 37

Intracellular Ca2+ concentrations in cardiac cells are dependent on trans-sarcolemmal Ca2+ fluxes and the ability of sarcoplasmic reticulum to release and take up Ca2+. Ca2+ accumulation by sarcoplasmic reticulum membranes causes muscle to relax, whereas Ca2+ release from sarcoplasmic reticulum initiates contraction. Ca2+ transport by the sarcoplasmic is mediated by a Ca2+-dependent ATPase enzyme. Ca2+ release from sarcoplasmic reticulum may be mediated by a ligant-gated Ca2+ channel. The physiological role of sarcoplasmic reticulum in developing muscle is not well established. In this report we investigated the composition and function of sarcoplasmic reticulum membranes during cardiac myogenesis. Phospholamban, a major phosphoprotein in mature sarcoplasmic reticulum membranes was present during early stages of cardiac myogenesis. The embryonic 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 to adult control membranes, although the apparent affinities of the enzyme for Ca2+ were similar. Sarcoplasmic reticulum vesicles used in these studies had very low levels of plasma membrane and mitochondrial contamination. The amounts of both 110-kDa Ca2+-ATPase and 55-kDa calsequestrin in the sarcoplasmic reticulum membrane were lower in fetal sarcoplasmic reticulum vesicles compared to mature membranes. Ca2+-ATPase and calsequestrin were identified in the isolated sarcoplasmic reticulum vesicles using specific antibodies produced against these membrane proteins. Age-related differences in Ca2+ transport properties of cardiac sarcoplasmic reticulum and in the amount of Ca2+-ATPase and calsequestrin may explain alterations in the regulation of intracellular Ca2+ concentrations in fetal heart muscle. This may relate to the developmental changes observed in myocardial function.
 ...
PMID:Sarcoplasmic reticulum membrane and heart development. 244 May 34

The structure of phospholamban, a 30-kDa oligomeric protein integral to cardiac sarcoplasmic reticulum, was probed using ultraviolet absorbance and circular dichroism spectroscopy. Purified phospholamban was examined in three detergents: octyl glucoside, n-dodecyloctaethylene glycol monoether (C12E8) and sodium dodecyl sulfate (SDS). Ultraviolet absorption spectra of phospholamban reflected its aromatic amino acid content: absorption peaks at 275-277 nm and 253, 259, 265 and 268 nm were attributed to phospholamban's one tyrosine and two phenylalanines, respectively. Phospholamban phosphorylated at serine 16 by the catalytic subunit of cAMP-dependent protein kinase exhibited no absorbance changes when examined in C12E8 or SDS. Circular dichroism spectroscopy at 250-190 nm demonstrated that phospholamban possesses a very high content of alpha-helix in all three detergents and is unusually resistant to denaturation. Dissociation of phospholamban subunits by boiling in SDS increased the helical content, suggesting that the highly ordered structure is not dependent upon oligomeric interactions. The purified COOH-terminal tryptic fragment of phospholamban, containing residues 26-52 and comprising the hydrophobic, putative membrane-spanning domain, also exhibited a circular dichroism spectrum characteristic of alpha-helix. Circular dichroism spectra of phosphorylated and dephosphorylated phospholamban were very similar, indicating that phosphorylation does not alter phospholamban secondary structure significantly. The results are consistent with a two-domain model of phospholamban in which each domain contains a helix and phosphorylation may act to rotate one domain relative to the other.
 ...
PMID:Secondary structure of detergent-solubilized phospholamban, a phosphorylatable, oligomeric protein of cardiac sarcoplasmic reticulum. 252 65

Muscarinic cholinergic agonists such as acetylcholine attenuate phosphorylation of phospholamban induced by agents that activate cAMP-dependent protein kinase. However, cAMP accumulation is variably affected or only slightly reduced; thus, the choline ester might produce effects in addition to inhibition of adenylate cyclase. We hypothesized that acetylcholine might regulate a phosphatase in mammalina myocardium. Exposure of Langendoff-perfused guinea pig ventricles to isoproterenol (10 nM) for 45 s increased phosphatase inhibitor-1 activity 2-fold. Co-administration of acetylcholine (100 nM) antagonized the effect of isoproterenol, and atropine (1 microM) blocked the effect of acetylcholine. Forskolin (1 microM) caused a 3-fold increase in inhibitor-1 activity, and acetylcholine markedly attenuated the effect of forskolin. However, acetylcholine did not lower cAMP levels in the same tissues. Both isoproterenol and forskolin reduced the type 1 phosphatase activity intrinsic to sarcoplasmic reticulum by 25-50%, using [32P]phosphorylase a or 32P-labeled membrane vesicles as a substrate for the phosphatase. Co-administration of acetylcholine markedly attenuated these effects of isoproterenol and forskolin. Acetylcholine alone caused a 50% increase in type 1 phosphatase activity. We concluded that inhibitor-1 and type 1 phosphatase can be regulated in intact cardiac muscle by agents that increase intracellular cAMP and by acetylcholine.
 ...
PMID:Autonomic regulation of type 1 protein phosphatase in cardiac muscle. 253 94

Highly purified sarcoplasmic reticulum (SR) has been prepared from dog hearts and has been incubated with the triplet probe erythrosinyl isothiocyanate to specifically label the Ca2+-stimulated ATPase (Ca2+-ATPase) of the SR. The rotational mobility of the Ca2+-ATPase has been studied in this erythrosin-labelled SR using time-resolved phosphorescence polarization. Qualitatively, the mobility of the cardiac Ca2+-ATPase resembles that of skeletal muscle SR Ca2+-ATPase. Addition of Ca2+ to SR affects the mobility of the Ca2+-ATPase in a way consistent with a segment of the ATPase altering its orientation relative to the plane of the membrane. Phosphorylation of phospholamban in cardiac SR by the purified catalytic subunit of cAMP-dependent protein kinase, which is known to increase the activity of the Ca2+-ATPase by deinhibition, also alters measured anisotropy. The changes observed are not compatible with dissociation of the Ca2+-ATPase from phospholamban after the latter is phosphorylated. The data are more consistent with phospholamban associating with the Ca2+-ATPase following phosphorylation, or more complex models in which only the hydrophilic domain of phospholamban binds with and dissociates from the Ca2+-ATPase.
 ...
PMID:The effects of calcium, temperature and phospholamban phosphorylation on the dynamics of the calcium-stimulated ATPase of canine cardiac sarcoplasmic reticulum. 254 Aug 39

Phospholamban is the major membrane protein of the heart phosphorylated in response to beta-adrenergic stimulation. In cell-free systems, cAMP-dependent protein kinase catalyzes exclusive phosphorylation of serine 16 of phospholamban, whereas Ca2+/calmodulin-dependent protein kinase gives exclusive phosphorylation of threonine 17 (Simmerman, H. K. B., Collins, J. H., Theibert, J. L., Wegener, A. D., and Jones, L. R. (1986) J. Biol. Chem. 261, 13333-13341). In this work we have localized the sites of phospholamban phosphorylation in intact ventricles treated with the beta-adrenergic agonist isoproterenol. Isolation of phosphorylated phospholamban from 32P-perfused guinea pig ventricles, followed by partial acid hydrolysis and phosphoamino acid analysis, revealed phosphorylation of both serine and threonine residues. At steady state after isoproterenol exposure, phospholamban contained approximately equimolar amounts of these two phosphoamino acids. Two major tryptic phosphopeptides containing greater than 90% of the incorporated radioactivity were obtained from phospholamban labeled in intact ventricles. The amino acid sequences of these two tryptic peptides corresponded exactly to residues 14-25 and 15-25 of canine cardiac phospholamban, thus localizing the sites of in situ phosphorylation to serine 16 and threonine 17. Phosphorylation of phospholamban at two sites in heart perfused with isoproterenol was supported by detection of 11 distinct mobility forms of the pentameric protein by use of the Western blotting method, consistent with each phospholamban monomer containing two phosphorylation sites, and with each pentamer containing from 0 to 10 incorporated phosphates. Our results localize the sites of in situ phospholamban phosphorylation to serine 16 and threonine 17 and, furthermore, are consistent with the phosphorylations of these 2 residues being catalyzed by cAMP- and Ca2+/calmodulin-dependent protein kinases, respectively.
 ...
PMID:Phospholamban phosphorylation in intact ventricles. Phosphorylation of serine 16 and threonine 17 in response to beta-adrenergic stimulation. 254 95


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