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:2.7.11.11 (AMPK)
12,425 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have identified and highly purified a "low Km" cAMP phosphodiesterase from bovine cardiac muscle. This phosphodiesterase was inhibited by low concentrations of cGMP and has, therefore, been temporarily designated as cGMP-inhibited phosphodiesterase. After a 16,000-fold increase in specific activity, the highly purified enzyme had a specific activity of 6 mumol/min-mg and contained three major polypeptides. Initial data indicated that all of these polypeptides were derived from a single common precursor by proteolysis. We used this enzyme preparation to generate polyclonal antisera and monoclonal antibodies directed against the "low Km" phosphodiesterase. Immunoadsorption and immunoblot analysis allowed us to identify and isolate several molecular weight species of phosphodiesterase, including a larger form than previously reported for any purified low Km phosphodiesterase. This large form of the enzyme had a subunit molecular weight of approximately 110,000 and was the only one seen in fresh extracts of cardiac muscle. Full catalytic activity was recovered in the phosphodiesterase-antibody complex and enzyme prepared by immunoprecipitation exhibited Michaelis-Menten kinetics for cAMP hydrolysis and for inhibition by cGMP. The Km for cAMP hydrolysis was 0.15 microM and the Ki for cGMP inhibition of cAMP hydrolysis was 0.06 microM. This immunoprecipitation approach also allowed us to determine that the enzyme was phosphorylated on serine residues by cAMP-dependent protein kinase, and that the low Km, cGMP-inhibited phosphodiesterase was selectively inhibited by several new cardiotonic agents. Milrinone, amrinone, and fenoximone were highly selective inhibitors of this isozyme, and the relative affinities of these inhibitors were consistent with their order of potency as positive inotropic agents. These studies suggest that the cGMP-inhibited phosphodiesterase is a receptor for several new cardiotonic drugs.
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PMID:Isolation and characterization of bovine cardiac muscle cGMP-inhibited phosphodiesterase: a receptor for new cardiotonic drugs. 301 79

Calmodulin-dependent protein phosphatase purified from bovine cardiac muscle catalyzed the rapid dephosphorylation of Ser-95 of bovine cardiac cAMP-dependent protein kinase regulatory subunit (RII). The kinetic constants determined for the reaction (Km = 20 microM; Vmax = 2 mumol min-1 mg-1) are comparable to those determined for other good substrates of this phosphatase. Because little is known about the determinants of substrate specificity for the calmodulin-dependent phosphatase, various phosphopeptides were used to investigate the structural features important for substrate recognition. Limited proteolysis of phospho-RII with trypsin and chymotrypsin yielded fragments (residues 93-400 and 91-400, respectively) that were poor substrates, whereas digestion with Staphylococcal aureus V8 protease produced three phosphopeptides that were all dephosphorylated as rapidly as intact RII. The sequence of the shortest phosphopeptide produced by S. aureus V8 protease was determined by sequence analysis to be Asp-Leu-Asp-Val-Pro-Ile-Pro-Gly-Arg-Phe-Asp-Arg-Arg-Val-Ser-Val-Cys-Ala-Glu, corresponding to residues 81-99 of RII. Synthetic phosphopeptides corresponding to residues 81-99, 85-99, 90-99, and 91-99 were prepared to determine the minimum sequence necessary for substrate recognition. Only the 19-residue peptide (81-99) was dephosphorylated with kinetics comparable to RII (Km = 26 microM, Vmax = 1.7 mumol min-1 mg-1). Structural analysis of this peptide indicates that an amphipathic beta-sheet structure may be an important structural determinant for some substrates of the calmodulin-dependent phosphatase.
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PMID:Dephosphorylation of cAMP-dependent protein kinase regulatory subunit (type II) by calmodulin-dependent protein phosphatase. Determinants of substrate specificity. 301 43

Incubation of Saccharomyces cerevisiae strain JR153 with either [3H]myristate or [3H]palmitate demonstrates the synthesis of proteins that contain covalently bound fatty acids. A unique set of proteins is labeled by each fatty acid. Detailed analysis of a 20-kDa protein labeled with myristic acid demonstrates that myristate is linked to the amino-terminal glycine. We describe an enzymatic activity in yeast that will transfer myristic acid to the amino terminus of the octapeptide Gly-Asn-Ala-Ala-Ala-Ala-Arg-Arg, whose sequence was derived from a known N-myristoylated acyl protein, the catalytic subunit of cAMP-dependent protein kinase of bovine cardiac muscle. The acylation reaction is dependent on ATP and CoA, is enriched in a crude membrane fraction, and will use myristate but not palmitate as the acyl donor. Specificity of the glycyl peptide substrate is demonstrated by the observation that other glycyl peptides do not competitively inhibit myristoylation of Gly-Asn-Ala-Ala-Ala-Ala-Arg-Arg.
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PMID:Protein fatty acid acylation: enzymatic synthesis of an N-myristoylglycyl peptide. 351 77

Electrophoretically homogeneous preparations of catalytic subunit (C) of cAMP-dependent protein kinase isolated according to two different procedures from holoenzyme type I and type II from rabbit and from holoenzyme type II from rat skeletal muscle and from bovine cardiac muscle can be separated on carboxymethyl cellulose or on a Mono S column (Pharmacia) by salt gradient elution into two enzymatically active peaks called A and B, which do not interconvert on rechromatography. Cochromatography of peak A fractions or of peak B fractions derived from both holoenzymes respectively yields single enzyme peaks in each case, thus indicating that both represent different entities, which were named CA and CB. The separate character of both enzyme forms is supported by the fact that CB under all conditions is degraded faster by the C-specific protease (E. Alhanaty et al. (1981) Proc. Natl. Acad. Sci. USA 78, 3492-3495) than CA, a phenomenon which is enhanced in both enzyme forms by substrate (Kemptide). The separation of both subtypes from each other is probably based on differences in isoelectric values (delta pH less than or equal to 0.5 units). The reason for the charge difference is not presently known. CA and CB do not differ significantly in their phosphate content. No differences between CA and CB have been detectable so far with respect to their migration in SDS gels, kinetic behavior regarding both substrates and cosubstrate, pH dependence, inhibition by regulatory subunits of holoenzyme type I (rabbit skeletal muscle) and of type II (bovine cardiac muscle), and inhibition by specific-heat and acid-stable inhibitor-modulator. The peptide pattern of both forms after limited proteolysis exhibits small differences.
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PMID:Chromatographic separation of two heterogeneous forms of the catalytic subunit of cyclic AMP-dependent protein kinase holoenzyme type I and type II from striated muscle of different mammalian species. 356 80

The interaction of the catalytic subunit of bovine cardiac muscle cAMP-dependent protein kinase with N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide (H-8), the most potent and selective inhibitor toward cyclic nucleotide-dependent protein kinases in the series of isoquinolinesulfonamide derivatives, was studied. The addition of H-8 protected the catalytic subunit of the enzyme in a dose-dependent manner from irreversible inactivation by the ATP analogue p-fluorosulfonylbenzoyl-5'-adenosine (FSBA). The inactivation followed pseudo-first order kinetics and H-8 reduced the steady state constant of inactivation (Ki) without any effect on the first order rate constant (K3). The quantitative binding of H-8 to the enzyme was measured under conditions of thermodynamic equilibrium using a gel filtration method. The catalytic subunit bound approximately 1 mol of drug/mol of protein with apparent half-maximal binding at 1.0 microM drug, whereas the enzyme irreversibly modified by FSBA did not bind the drug, confirming that the enzyme has no site for H-8 in the catalytic subunit other than the active site. The binding studies also showed that H-8 does not require divalent cations such as Mg2+ to bind to the catalytic subunit of the protein kinase. The binding of H-8 to the active site was characterized using FSBA and other affinity labeling reagents which have been postulated to modify residues at or near the active site of the catalytic subunit. H-8 protected the enzyme against inactivation by FSBA and Cibacron Blue F3GA but did not afford any protection against the covalent modification of 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) and 7-chloro-4-nitro-2,1,3-benzoxadiazole (NBD-Cl), suggesting that the binding site of H-8 does not involve the gamma-subsite of the ATP binding site in the catalytic subunit, since DTNB and NBD-Cl are thought to modify the residues complementary to gamma-phosphate of the ATP molecules.
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PMID:Specific binding of a novel compound, N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide (H-8) to the active site of cAMP-dependent protein kinase. 357 96

Catecholamines are known to influence the contractility of cardiac and skeletal muscles, presumably via cAMP-dependent phosphorylation of specific proteins. We have investigated the in vitro phosphorylation of myofibrillar proteins by the catalytic subunit of cAMP-dependent protein kinase of fast- and slow-twitch skeletal muscles and cardiac muscle with a view to gaining a better understanding of the biochemical basis of catecholamine effects on striated muscles. Incubation of canine red skeletal myofibrils with the isolated catalytic subunit of cAMP-dependent protein kinase and Mg-[gamma-32P]ATP led to the rapid incorporation of [32P]phosphate into five major protein substrates of subunit molecular weights (MWs) 143,000, 60,000, 42,000, 33,000, and 11,000. The 143,000 MW substrate was identified as C-protein; the 42,000 MW substrate is probably actin; the 33,000 MW substrate was shown not to be a subunit of tropomyosin and, like the 60,000 and 11,000 MW substrates, is an unidentified myofibrillar protein. Isolated canine red skeletal muscle C-protein as phosphorylated to the extent of approximately 0.5 mol Pi/mol C-protein. Rabbit white skeletal muscle and bovine cardiac muscle C-proteins were also phosphorylated by the catalytic subunit of cAMP-dependent protein kinase, both in myofibrils and in the isolated state. Cardiac C-protein was phosphorylated to the extent of 5-6 mol Pi/mol C-protein, whereas rabbit white skeletal muscle C-protein was phosphorylated at the level of approximately 0.5 mol Pi/mol C-protein. As demonstrated earlier by others, C-protein of skeletal and cardiac muscles inhibited the actin-activated myosin Mg2+-ATPase activity at low ionic strength in a system reconstituted from the purified skeletal muscle contractile proteins (actin and myosin).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Phosphorylation of skeletal and cardiac muscle C-proteins by the catalytic subunit of cAMP-dependent protein kinase. 375 98

C-protein, a thick filament-associated protein, has been isolated from bovine myocardium and found to be a substrate in vitro of the Ca2+- and phospholipid-dependent protein kinase (protein kinase C). Incorporation of approximately 1.6 mol Pi/mol C-protein was observed. This phosphorylation was dependent on both Ca2+ and a phospholipid (L-alpha-phosphatidyl-L-serine was used). Phosphate incorporation specifically into C-protein was verified by SDS-polyacrylamide gel electrophoresis and autoradiography and was almost exclusively into serine residues (86.9%), with only a small amount of phosphothreonine (13.1%) and no phosphotyrosine being detected. Two-dimensional thin-layer electrophoresis of a chymotryptic digest of phosphorylated C-protein indicated site specificity of phosphorylation. Cardiac C-protein is known to be a substrate of cAMP-dependent protein kinase both in vitro and in vivo (Jeacocke, S.A. and England, P.J. (1980) FEBS Lett. 122, 129-132). Isolated bovine cardiac C-protein was rapidly phosphorylated, to the extent of 5 mol/mol, by the purified catalytic subunit of cAMP-dependent protein kinase. Phosphorylation catalyzed by these two protein kinases was not additive, suggesting that the sites phosphorylated by protein kinase C are also phosphorylated by cAMP-dependent protein kinase. Chicken cardiac muscle has also been shown to contain a Ca2+, calmodulin-dependent protein kinase which phosphorylates C-protein (Hartzell, H.C. and Glass, D.B. (1984) J. Biol. Chem. 259, 15587-15596). The physiological role of cardiac C-protein may therefore be subject to regulation by multiple protein kinases.
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PMID:Phosphorylation of bovine cardiac C-protein by protein kinase C. 384 Sep 98

Chemically skinned (Lubrol WX) cardiac muscle fibers produce half-maximum isometric tension at pCa 6.18 (pH 6.7) in presence of MgATP (10 mM). After addition of cGMP (5 microM) and cGMP-dependent protein kinase (0.1 microM), the pCa required for half-maximum activation is 5.96, while maximum tension is not affected. Similar shifts in the tension/pCa-relationship have been observed after incubation of skinned cardiac muscle fibers with cAMP of catalytic subunit of the cAMP-dependent protein kinase. The shift in the Ca2+-sensitivity is associated with an increased incorporation of radioactivity into a Mr 28000 band (presumably troponin-I) and a Mr 145000 band.
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PMID:cGMP-dependent protein kinase decreases calcium sensitivity of skinned cardiac fibers. 618 64

In detergent-treated cardiac muscle fibers, forskolin, a potent activator of adenylate cyclases, inhibits tension development elicited with submaximal [Ca2+] and increases incorporation of 32P into troponin-I. A similar reduced tension development has been observed after treatment with cAMP or the catalytic subunit of the cAMP-dependent protein kinase. It is concluded that these fibers still contain much of the enzyme cascade involved in evoking a contractile response to beta-adrenergic stimulation.
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PMID:Forskolin inhibits tension development in detergent-treated cardiac muscle fibers. 619 1

A unique set of high molecular weight proteins was identified in junctional sarcoplasmic reticulum (SR) vesicles isolated from both cardiac muscle and skeletal muscle. These high Mr proteins were not present in free SR vesicles isolated from either tissue, nor were they observed in purified sarcolemmal fractions. The junctional SR high Mr proteins migrated as doublets in sodium dodecyl sulfate-polyacrylamide gels and exhibited apparent Mr values between 290,000 and 350,000. The high Mr proteins bound calmodulin; they were the principal proteins labeled in the cardiac and skeletal muscle SR subfractions by azido-125I-calmodulin. The high Mr proteins were also substrates for an endogenous Ca2+-calmodulin-dependent protein kinase activity, as well as exogenously added catalytic subunit of cAMP-dependent protein kinase. In addition, the junctional SR high Mr proteins were the major SR proteins degraded by a Ca2+-activated protease purified from smooth muscle. Control experiments verified the separation of junctional SR vesicles and free SR vesicles from both muscle types. Junctional SR vesicles were enriched in calsequestrin, and they exhibited Ca2+ uptake which was stimulated up to 10-fold by either ryanodine or ruthenium red. Free SR vesicles were deficient in calsequestrin and were insensitive to these two agents. Localization of the cardiac and skeletal muscle high Mr proteins to the junctional SR, coupled with demonstration of their nearly identical biochemical properties, suggests that the proteins are homologous and are likely to have similar functions in both types of striated muscle.
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PMID:High molecular weight proteins in cardiac and skeletal muscle junctional sarcoplasmic reticulum vesicles bind calmodulin, are phosphorylated, and are degraded by Ca2+-activated protease. 620 12


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