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)

Sarcolemma was isolated by fractionation of salt-extracted particles on two consecutive sucrose density gradients. Salt extraction of homogenates, rather than of washed particles, was found to preserve the activities of adenylate cyclase and ouabain-sensitive (Na+,-K+)-ATPase in the isolated sarcolemmal membranes. Purified sarcolemma contained substantial adenylate cyclase and guanylate cyclase activities that were stimulable by beta-adrenergic and muscarinic agonists, respectively. Significant ouabain-sensitive (Na+, K+)-ATPase activity as well as putative digitalis receptor activity was also present in sarcolemma. Cyclic nucleotide phosphodiesterases of sarcolemma, both cAMP- and cGMP-dependent, displayed positive cooperativity of substrate interactions; Ca2+ ions were found to increase the activity of the GMP-dependent enzyme.
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PMID:Isolation and enzymatic characterization of guinea pig cardiac sarcolemma. 2 1

Mitochondrial ATPases from rat liver and beef heart were used to study the effects of guanylylimidodiphosphate (GMP-P(NH)P) and adenylylimidodiphosphate (AMP-P(NH)P) on the kinetics of MgATP, MgITP, and MgGTP hydrolysis. AMP-P(NH)P was a noncompetitive inhibitor of hydrolysis of all substrates with the rat liver enzyme, whether activating anions were present or not. Also with the liver enzyme, AMP-P(NH)P caused only MgATP hydrolysis to appear to have positive cooperativity. With the beef heart enzyme, AMP-P(NH)P was a competitive inhibitor of ATPase activity and caused positive cooperativity; it gave noncompetitive patterns with GTP or ITP as substrates. In both enzyme systems, GMP-P(NH)P gave complex inhibition patterns with MgATP as the substrate, but was a competitive inhibitor of MgITP and MgGTP hydrolysis. These results are interpreted as indicating the existence of two types of nucleotide binding sites, with varying degrees of specificity and interaction on the ATPase molecules from both sources. It is postulated that MgATP and AMP-P(NH)P bind to regulatory site while MgATP, MgGTP, Mgitp, and GMP-P(NH)P bind to the catalytic site.
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PMID:Kinetic studies on rat liver and beef heart mitochondrial ATPase. Evidence for nucleotide binding at separate regulatory and catalytic sites. 12 41

Substances known to alter cyclic nucleotide levels in cells were applied to the isolated toad retina and effects on rod electrical and adaptive behavior were studied. The retina was continually superfused in control ringer's or ringer's containing one or a combination of drugs, and rod activity was recorded intracellularly. Superfusion with cGMP, Bu(2)GMP, isobutylmethylxanthine (IBMX; a phosphodiesterase inhibitor), or PGF(2alpha) (a prostaglandin) caused effects in rods that closely match those observed when extracellular Ca(2+) levels were lowered. For example, short exposures (up to 6 min) of the retina to these substances caused depolarization of the membrane potential, increase in response amplitudes, and some changes in waveform; but under dark-adapted or partially light-adapted conditions receptor sensitivity was virtually unaffected. That is, the position of the V-log I curve on the intensity axis was determined by the prevailing light level, not by drug level. These drugs, like lowered extracellular Ca(2+), also decreased the period of receptor saturation after a bright-adapting flash, resulting in an acceleration of the onset of membrane and sensitivity recovery during dark adaptation. Long-term (6-15 min) exposure of a dark-adapted retina to 5 mM IBMX or a combination of IBMX and cGMP caused a loss of response amplitude and a desensitization of the rods that was similar to that observed in rods after a long-term low Ca(2+) (10(-9)M) treatment. Application of high (3.2 mM) Ca(2+) to the retina blocked the effects of applied Bu(2)cGMP. PGE(1) superfusion mimicked the effects of increasing extracellular Ca(2+). The results show that increased cGMP and lowered Ca(2+) produce similar alterations in the electrical activity of rods. These findings suggest that Ca(2+) and cGMP are interrelated messengers. We speculate that low Ca(2+) may lead to increased intracellular cGMP, and/or that applied cGMP, and/or that applied cGMP may lower cytosol Ca(2+), perhaps by stimulating Ca(2+)- ATPase pumps in the outer segment.
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PMID:Electrical and adaptive properties of rod photoreceptors in Bufo marinus. II. Effects of cyclic nucleotides and prostaglandins. 20 24

The mechanism of the Mg2+-dependent myosin subfragment 1 catalyzed hydrolysis of GTP and 2-amino-6-mercapto-9-beta-ribofuranosylpurine 5'-triphosphate (thioGTP) has been investigated by rapid-reaction techniques. The myosin was isolated from rabbit skeletal muscle. The steady-state intermediate of these reactions consists pre-dominantly of a protein-substrate complex unlike the myosin subfragment 1 ATPase reaction which has a protein-products complex as the principal steady-state component. The mechanism of GTP hydrolysis catalyzed by subfragment 1 has other marked differences from the ATPase mechanism. The second-order rate constant of binding of GTP to subfragment 1 is tenfold greater than that for GDP binding. The dissociation rate constant of GDP from subfragment 1 is 0.06 s-1 compared with the subfragment 1 catalytic center activity for GTP hydrolysis of 0.5 s-1 at pH 8.0 and 20 degrees C. This shows that GDP bound to subfragment 1 forms a complex which is not kinetically competent to be an intermediate of the GTPase mechanism. GDP is hydrolyzed in the presence of subfragment 1 to GMP and Pi. The subfragment 1 GTPase mechanism has a nuber if features in common with that of the elongation factor Tu GTPase of the protein biosynthetic system of Escherichia coli.
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PMID:Magnesium ion dependent rabbit skeletal muscle myosin guanosine and thioguanosine triphosphatase mechanism and a novel guanosine diphosphatase reaction. 22 6

To clarify the kinetics of cell membrane and intracellular mediators in the process of auranofin (AF)-induced diarrhea, we perfused electrolyte solution containing the oral gold preparation AF, which is a treatment for rheumatoid arthritis, through the rat jejunum, and studied net water and electrolyte transport, Na+, K(+)-ATPase activity, and c-AMP and c-GMP concentrations in the jejunal mucosa. In addition, change in Ca+ concentration in isolated intestinal cells was evaluated using fura-2-acetoxyl-methyl ester. AF significantly suppressed water and electrolyte transport. Mucosal secretion was increased due to elevation of the intracellular Ca+ concentration early in the perfusion period, then due to reduction in the Na+, K(+)-ATPase activity, and increase in the c-AMP concentration late in the perfusion period. Therefore, these cell membranes and intracellular mediators are considered to be involved in the mechanism of AF-induced diarrhea.
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PMID:[Experimental study of the mechanism of auranofin-induced diarrhea]. 131 15

Protein lambda 2 of reovirus serotype 3 has been purified to homogeneity from extracts of cells infected with hybrid vaccinia virus strain WR into whose TK gene of the reovirus L2 genome segment under the control of the CPV ATI protein gene promoter had been inserted. Protein lambda 2 is formed in large amounts (final purification factor about 180) as a monomer that shows no tendency to pentamerize into the reovirus core projections/spikes. Isolated protein lambda 2 is reversibly guanylylated by GTP (that is, it carries out the GTP-PPi exchange reaction) and can transfer the -GMP moiety to GTP to form GppppG, to GDP to form GpppG, and to 5'-pp-terminated RNA to form GpppG- caps. These studies confirm previous studies on reovirus cores that indicated that protein lambda 2 is the reovirus guanylyltransferase. Protein lambda 2 possesses neither nucleoside nor RNA triphosphatase activities, nor methyltransferase activities; thus it is the reovirus capping enzyme, but provides neither the required 5'-ppG-terminated substrate nor does it methylate the cap structure. These must be functions of lambda 2 pentamers or of other individual or complexed components of reovirus cores.
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PMID:Isolation and enzymatic characterization of protein lambda 2, the reovirus guanylyltransferase. 165 91

The Ca(2+)-pump ATPases of the plasma membrane and of the endoplasmic reticulum play an important role in controlling the intracellular Ca(2+)-concentration. In this perspective it is not unexpected that these enzymes are modulated by different factors. The activity of the plasmalemmal (Ca2+ +Mg2+)ATPase is modified by the amount of negatively charged phospholipids surrounding the enzyme. Some evidence is presented indicating that in stomach and myometrium smooth muscle agonists inhibit the extrusion of Ca2+ by reducing the negatively charged phospholipids surrounding the plasmalemmal Ca(2+)-pump, while c-GMP dependent protein kinase would activate this Ca(2+)-pump by increasing this amount. The regulation of the Ca(2+)-pump of the endoplasmic reticulum depends on the phosphorylation of phospholamban by cAMP- and cGMP-dependent protein kinase. In the second part of this review, the heterogeneity of the intracellular Ca2+ compartments and a possible connection between the intracellular compartment and the extracellular solution are discussed. In addition, some data on the regulation of Ca2+ inside the nucleus are presented.
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PMID:Ca(2+)-transport ATPases and Ca(2+)-compartments in smooth muscle cells. 166 64

Calmodulin is a small protein (16.7 KDa) calcium receptor which plays a fundamental part in vasomotricity. When intracellular Ca2+ concentrations increase (from 0.1 to 10 M), calmodulin fixes four Ca2+, changes its conformation and interacts with its target proteins. In vascular smooth muscle it activates the kinase of the myosine light chain and interacts with caldesmone to allow phosphorylation of myosine and the actine-myosine interaction. These two processes lead to vascular smooth muscle contraction. Calmodulin also activates enzymes involved in the regulation of the cyclic nucleotides: adenylate cyclase which synthesises cyclic AMP and the calmodulin dependent phophodiesterase which preferentially hydrollyses cyclic GMP. Cyclic AMP and GMP contribute to the relaxation of smooth muscle by inhibiting, the kinase of the myosine light chain and stimulating the Ca2+ ATPase responsible for the extrusion of Ca2+. The contractile action of calmodulin is counterbalanced by the relaxing effects of cyclic AMP and GMP. In addition, caldomodulin participates in the control of vasomotricity by regulating the phosphorylation and dephosphorylation of proteins influencing intracellular Ca2+ concentrations and the activation of contractile proteins. Caldomodulin activates the enzyme responsible for the synthesis of nitric oxide in the endothelium (endothelium derived relaxing factor) and thereby participates in the endothelium dependent relaxation process.
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PMID:[Calcium-calmodulin and vasomotor activity]. 205 31

The role of 48-kDa protein in visual transduction remains unresolved. Two hypotheses for its role in quenching the light activation of cyclic GMP cascade suggest that the protein binds to either phosphodiesterase or phosphorylated rhodopsin. Since the protein is also reported to bind ATP, we anticipated that the protein may have ATP hydrolyzing activity, and in analogy with the GTP-binding protein of the rod outer segments, such activity may be greatly enhanced by the elements of transduction cyclic GMP cascade, permitting the protein to function cyclically as GTP-binding protein does. We found that purified 48-kDa protein hydrolyzes ATP but at a slow rate of 0.04-0.05 per min. The Km for ATP is about 45-65 microM. The activity is inhibited noncompetitively by ADP with a Ki of about 50 microM. The ATPase activity of 48-kDa protein is not affected by rhodopsin, bleached rhodopsin, phosphorylated rhodopsin, unactivated cyclic GMP phosphodiesterase, or phosphodiesterase (PDE) activated by GMP PNP-bound G-protein. These data show that although 48-kDa protein has ATPase activity, lack of regulation of this activity by the elements of visual transduction makes it unlikely for this activity to have a role in quenching the light activation of cyclic GMP cascade.
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PMID:Photoreceptor rod outer segment 48-kDa protein has ATPase activity. 215 Jul 55

RNA triphosphatase, RNA guanylyltransferase, RNA (guanine-7)-methyltransferase, and transcription termination factor activities are associated with the mRNA capping enzyme from vaccinia virus. Purified vaccinia capping enzyme is a 6.5 S protein containing two subunits of Mr = 95,000 and Mr = 31,000. Although the RNA guanylyltransferase domain has been localized to the large subunit by virtue of the formation of a Mr = 95,000 covalent protein-GMP intermediate, the location of other functional domains within the protein and the catalytic role of individual subunits remain unclear. In the present study, limited proteolysis with trypsin was shown to convert the vaccinia capping enzyme into a form capable of generating a Mr = 59,000 enzyme-GMP complex. Purification of the trypsinized enzyme by glycerol gradient sedimentation resulted in the isolation of a 4.2 S fragment of the large subunit that retains RNA triphosphatase and RNA guanylyltransferase activities. This derivative, containing little or no small subunit (or fragments thereof), has lost the ability to catalyze methyl group transfer and to mediate transcription termination in vitro. Residual methyltransferase activity was found associated with a minor 5.2 S tryptic product that cosediments with a Mr = 21,000 fragment of the small enzyme subunit. A model for the organization of functional domains within the capping enzyme is suggested.
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PMID:Functional domains of vaccinia virus mRNA capping enzyme. Analysis by limited tryptic digestion. 254 18


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