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

Phospholamban, a putative regulator of cardiac sarcoplasmic reticulum Ca2+ transport, has been shown to be phosphorylated in vitro by cAMP-dependent protein kinase and an intrinsic Ca2+-calmodulin-dependent protein kinase activity. This study was conducted to determine if Ca2+-calmodulin-dependent phosphorylation of phospholamban occurs in response to physiologic increases in intracellular Ca2+ in intact myocardium. Isolated guinea pig and rat ventricles were perfused with 32Pi after which membrane vesicles were isolated from individual hearts by differential centrifugation. Administration of isoproterenol (10 nM) to perfused hearts stimulated 32P incorporation into phospholamban, Ca2+-ATPase activity, and Ca2+ uptake of sarcoplasmic reticulum isolated from these hearts. These biochemical changes were associated with increases in contractility and shortening of the t 1/2 of relaxation. Elevated extracellular Ca2+ produced comparable increases in contractility but failed to stimulate phospholamban phosphorylation or Ca2+ transport and did not alter the t 1/2 of relaxation. Inhibition of trans-sarcolemmal Ca2+ influx by perfusing the ventricles with reduced extracellular Ca2+ (50 microM) attenuated the increases in 32P incorporation produced by 10 nM isoproterenol. Trifluoperazine (10 microM) also attenuated isoproterenol-induced increases in 32P incorporation into phospholamban. In both cases, Ca2+ transport was reduced to a degree comparable to the reduction in phospholamban phosphorylation. These results suggest that direct physiologic increases in intracellular Ca2+ concentration do not stimulate phospholamban phosphorylation in intact functioning myocardium. Ca2+-calmodulin-dependent phosphorylation of phospholamban may occur in response to agents which stimulate cAMP-dependent mechanisms in intact myocardium.
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PMID:Phosphorylation of phospholamban in intact myocardium. Role of Ca2+-calmodulin-dependent mechanisms. 315 59

Two endogenous protein kinase activities, cAMP-dependent and calmodulin-Ca2+-dependent, are associated with isolated cardiac sarcoplasmic reticulum (SR) vesicles. Both kinases phosphorylate an endogenous substrate of approximately 22,000 daltons (phospholamban). The phosphorylation of phospholamban by either the intrinsic or by exogenous cAMP-dependent protein kinase is found to be Ca2+-independent between 0.05 and 100 microM free Ca2+. Calmodulin-dependent phosphorylation, on the other hand, does not require cAMP and is absolutely dependent on the presence of free Ca2+ over a concentration range that corresponds to physiological levels (10(-7) to 10(-5) M). Phosphorylation of SR vesicles by both kinases is additive and the extent of saturation of the cAMP-specific sites has no effect on the degree of stimulation by calmodulin or its Ca2+-dependence. Trifluoperazine, an inhibitor of calmodulin, inhibits calmodulin-dependent phosphorylation without affecting cAMP-dependent phosphorylation, indicating the presence of two types of kinases. This is made further evident by the selectivity of each kinase for exogenous substrates. Whereas cAMP-dependent protein kinase appears to phosphorylate histone ILA (a basic protein) preferentially, calmodulin-dependent protein kinase prefers phosvitin (an acidic protein).
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PMID:Studies on phosphorylation of canine cardiac sarcoplasmic reticulum by calmodulin-dependent protein kinase. 627 7

As in other cells, cAMP-dependent (protein kinase A) and calcium-dependent protein kinases are present in the rabbit peritoneal neutrophil. The major substrates for protein kinase A in the cytosol of rabbit peritoneal neutrophil is a 43 kDa protein which appears to be actin (pI 5.7). The other substrates for protein kinase A in the cytosol are very acidic proteins with molecular weights of 135000 (pI 4.6) and 130 000 (pI 4.8). Two classes of calcium-dependent protein kinases are present in the rabbit peritoneal neutrophil: one is calcium, calmodulin-dependent, the other is calcium, phosphatidylserine-dependent. Phosphatidylserine appears to be much more effective than calmodulin in stimulating calcium-dependent protein kinase activity. The phospholipid-sensitive, calcium-dependent protein kinase (protein kinase C), present only in the cytosol fraction, exhibits much higher activity than the cAMP-dependent protein kinase from the same source. At least four substrates (Mr 130 000 (pI 4.6) 43 000 (pI 4.8), 41 000 (pI 6.3) and 34 000) of the protein kinase C in the cytosol were identified. Trifluoperazine, a compound which inhibits the degranulation, aggregation and stimulated oxygen consumption of rabbit peritoneal neutrophils. (Alobaidi, T., Naccache, P.H. and Sha'afi, R.I. (1981) Biochim. Biophys. Acta 675, 316-321), also inhibits the activity of protein kinase C. The possible role of cAMP-dependent and calcium-dependent phosphorylation system in neutrophil function is discussed.
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PMID:Endogenous substrates for cyclic AMP-dependent and calcium-dependent protein phosphorylation in rabbit peritoneal neutrophils. 631 Dec 79

The characteristics of contraction and relaxation of membrane skinned smooth muscle from guinea pig trachealis muscle are described. Micromolar Ca2+ elicited reproducible contractions in Mg-ATP salt solution at 20 degrees C. The speed of contraction was much faster at 30 and 37 degrees C, enabling cumulative concentration-response curves to be obtained. At these temperatures, a progressive increase in basal tension occurred in the absence of Ca2+. This tension was active and developed more rapidly at pH 6.7 than at pH 7.0. Calmodulin (0.1-10 microM) greatly increased the speed of contraction and lowered the threshold Ca2+ concentration ([Ca2+]) required to initiate contraction from 0.13 to 0.02 microM Ca2+. Trifluoperazine antagonized responses to Ca2+. Thiophosphorylation with adenosine 5'-O-(3-thiotriphosphate) produced maximum tension development, which was Ca2+-independent. This effect was reversible. The results are compatible with myosin-linked regulation of contraction in which a Ca2+ X calmodulin complex activates myosin light chain kinase to phosphorylate myosin. The catalytic subunit of cAMP-dependent protein kinase strongly inhibited tension development and slowly relaxed fibers contracted with threshold [Ca2+] consistent with an action via phosphorylation of myosin light chain kinase. This effect was extremely slow compared with the rate of relaxation by Ca2+ withdrawal or with relaxation of intact smooth muscle by beta-adrenergic agonists.
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PMID:Effect of calmodulin, Ca2+, and cAMP protein kinase on skinned tracheal smooth muscle. 670 44

Ca2+/calmodulin- and cAMP-dependent protein kinase activities were characterized in two subcellular membrane samples. Membranes from rat lacrimal gland were isolated by differential and density gradient centrifugation into six density windows. The present study focused on membranes from density windows III and V which contain mixtures of apical, Golgi, endosomal, and endoplasmic reticulum membranes in different proportions. Phosphorylation of membrane proteins was measured by incubating the samples in [g-32P]ATP and separating the proteins by discontinuous SDS-PAGE followed by autoradiography. The amount of phosphate incorporated into specific peptide bands was quantified by densitometry. Ca2+/calmodulin-dependent protein kinase phosphorylated a 52,000 MW peptide in membranes from both density windows with a maximal increase from 0.3 to 66 microM free Ca2+. Trifluoperazine and promethazine, two inhibitors of Ca2+/calmodulin-dependent protein kinases, inhibited this phosphorylation. cAMP-dependent protein kinase phosphorylated a 22,000 MW peptide and a 91,000 MW peptide which were present in membranes from density window III only. We conclude that a Ca2+/calmodulin-dependent protein kinase activity is present in membranes from both density window III and V whereas a cAMP-dependent protein kinase activity is present only in membranes from density window III.
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PMID:Protein phosphorylation in Golgi, endosomal, and endoplasmic reticulum membrane fractions of lacrimal gland. 867 Jul 24