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)

The mechanism of biosynthetic, transferase, ATPase, and transphosphorylation reactions catalyzed by unadenylylated glutamine synthetase from E. coli was studied. Activation complex(es) involved in the biosynthetic reaction are produced in the presence of either Mg2+ or Mn2+ ; however, with the Mn2+-enzyme inhibition by the product, ADP, is so great that the overall forward biosynthetic reaction cannot be detected with the known assay methods. Binding studies show that substrates (except for NH3 and NH2OH which are not reported here) can bind to the enzyme in a random manner and that binding of the ATP-glutamate, ADP-Pi or ADP-arsenate pairs is strongly synergistic. Inhibition and binding studies show that the same binding site is utilized for glutamate and glutamine in biosynthetic and transferase reactions, respectively, and that a common nucleotide binding site is used for all reactions studied. Studies of the reverse biosynthetic reaction and results of fluorescent titration experiments suggest that both arsenate and orthophosphate bind at a site which overlaps the gamma-phosphate site of nucleoside triphosphate. In the reverse biosynthetic and transferase reactions, ATP serves as a substrate for the Mn2+-enzyme but not for the Mg2+-enzyme. The ATP supported transferase activity of Mn2+-enzyme is probably facilitated by the generation of ADP through ATP hydrolysis. When AMP was the only nucleotide substrate added, it was converted to ATP with concomitant formation of two equivalents of glutamate, under the reverse biosynthetic reaction conditions, and no ADP was detected. The reversibility of 180 transfer between orthophosphate and gamma-acyl group of glutamate was confirmed. ATPase activity of Mg2+ and Mn2+ unadenylylated enzymes is about the same. Both enzymes forms catalyze transphosphorylation reactions between various purine nucleoside triphosphates and nucleoside diphosphates under biosynthetic reaction conditions. The data are consistent with the hypothesis that a single active center is utilized for all reactions studied. Two stepwise mecanisms that could explain the results are discussed.
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PMID:Mechanistic studies of glutamine synthetase from Escherichia coli. An integrated mechanism for biosynthesis, transferase, ATPase reaction. 0 53

Reversible gamma-PO3 transfer in ATP reactions can be recognized by exchange of 18O from the beta,gamma-bridge position to the beta-P-nonbridge positions: (see article). Such intramolecular exchange is less demanding for the detection of the bond cleavage than the usual ATP:ADP isotope exchange because it does not require dissociation of bound ADP from the intermediate complex. Acyl phosphate intermediates are indicated for the glutamine synthetase and carbamyl-P synthetase reactions by their extreme requirements for glutamate and bicarbonate, respectively, for positional oxygen exchange. No support is given for E-P or concerted mechanisms. No support is found for an active CO2 in the latter reaction, although this is not ruled out by the data. Positional isomerization in ATP occurs with lamellae from spinach chloroplast only in the light. When the ATP molecule interacts, it also undergoes complete exchange of the gamma-PO3 oxygen with water before it rejoins the pool of free ATP. The difference in rates of the two exchanges suggests that the torsional motion of ADP-beta-PO3 is greatly hindered on the enzyme. This may explain, by the argument of substrate activation, the rapid reversibility of the ATPase reaction on the enzyme.
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PMID:Enzyme reactions of ATP studied by positional isotope exchange. 3 5

Chronic ammonia toxicity in experimental mice was induced by exposing them for 2 and 5 days to 5 % (v/v) ammonia solution. The enzymes concerned with glutamate metabolism (aspartate-, alanine- and tyrosine aminotransferases, glutamate dehydrogenase and glutamine synthetase) and (Na+ + K+)-ATPase were estimated in the three regions of brain (cerebellum, cerebral cortex and brain stem) and in liver. Glutamate, aspartate, alanine, glutamine and GABA, RNA and protein were also estimated in the three regions of brain and liver. A significant rise in the activity of (Na+ + K+)-ATPase in all the three regions of brain along with a fall in the activity of alanine aminotransferase was noticed. Changes in the activities of other enzymes were also observed. A significant increase in alanine and a decrease in glutamic acid was observed while no change was observed in the content of other amino acids belonging to the glutamate family. As a result of this, changes in the ratios of glutamate/glutamine and glutamate + aspartate/GABA was observed. The results indicated that the brain was in a state of more depression and less of excitation. Under these conditions the liver tissue was showing a profound rise in the activity of the enzymes of glutamate metabolism. The results are further discussed.
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PMID:Chronic metabolic effects of ammonia in mouse brain. 9 19

Ubiquinol-1 in aerated aqueous solution inactivates several enzymes--alanine aminotransferase, alkaline phosphatase, Na+/K(+)-ATPase, creatine kinase and glutamine synthetase--but not isocitrate dehydrogenase and malate dehydrogenase. Ubiquinone-1 and/or H2O2 do not affect the activity of alkaline phosphatase and glutamine synthetase chosen as model enzymes. Dioxygen and transition metal ions, even if in trace amounts, are essential for the enzyme inactivation, which indeed does not occur under argon atmosphere or in the presence of metal chelators. Supplementation with redox-active metal ions (Fe3+ or Cu2+), moreover, potentiates alkaline phosphatase inactivation. Since catalase and peroxidase protect while superoxide dismutase does not, hydrogen peroxide rather than superoxide anion seems to be involved in the inactivation mechanism through which oxygen active species (hydroxyl radical or any other equivalent species) are produced via a modified Haber-Weiss cycle, triggered by metal-catalyzed oxidation of ubiquinol-1. The lack of efficiency of radical scavengers and the almost complete protection afforded by enzyme substrates and metal cofactors indicate a 'site-specific' radical attack as responsible for the oxidative damage.
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PMID:Enzyme inactivation by metal-catalyzed oxidation of coenzyme Q1. 135 46

Transcription of the Ntr regulon is controlled by the two-component system consisting of the response regulator NRI (NtrC) and the kinase/phosphatase NRII (NtrB), which both phosphorylates and dephosphorylates NRI. Even though in vitro transcription from nitrogen-regulated promoters requires phosphorylated NRI, NRII-independent activation of NRI also occurs in vivo. We show here that this activation likely involves acetyl phosphate; it is eliminated by mutations that reduce synthesis of acetyl phosphate and is elevated by a mutation expected to cause accumulation of acetyl phosphate. With purified components, we investigated the mechanism by which acetyl phosphate stimulates glutamine synthetase synthesis. Acetyl phosphate, carbamyl phosphate, and phosphoramidate but not ATP or phosphoenolpyruvate acted as substrates for the autophosphorylation of NRI in vitro. Phosphorylated NRI produced by this mechanism exhibited the properties associated with NRI phosphorylated by NRII, including the activated ATPase activity of the central domain of NRI and the ability to activate transcription from the nitrogen-regulated glutamine synthetase glnAp2 promoter.
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PMID:Role of phosphorylated metabolic intermediates in the regulation of glutamine synthetase synthesis in Escherichia coli. 135 64

A spin-labeled ATP analogue, 2,2,6,6-tetramethylpiperidine-1-oxyl adenosine triphosphatase (Tempo-ATP) is used to adenylate Escherichia coli glutamine synthetase (L-glutamine: ammonia ligase (ADP-forming), EC 6.3.1.2). The Tempo adenylylated glutamine synthetase (Tempo-GS) exhibits similar catalytic properties, pH profile and inhibitor susceptibility as those of glutamine synthetase adenylylated with normal ATP. Using the spin label on the enzyme as a probe and employing the spin-spin interactions between the label probe and paramagnetic Mn2+, the distances from the nitroxyl moiety of the covalently bound Tempo-AMP to the two Mn2+ binding sites, n1 and n2 were determined. The n1 site is the structural site and n2 is located at the catalytic site. The distances from Mn2+ at n1 and n2 sites to the nitroxyl radical are 19 and 16 A, respectively. Binding of the substrate, L-Glu, causes a protein conformational change which is reflected by the reduction of approximately 2 A for the n1 to Tempo-AMP distance and lengthening of approximately 2 A for the n2 to the Tempo-AMP distance. Addition of ATP to the Tempo-GS/L-Glu complex increases the distance between n1 and Tempo-AMP, and n2 and Tempo-AMP by 4 and 3 A, respectively.
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PMID:Distance changes at the regulatory and catalytic sites on Escherichia coli glutamine synthetase: a spin label study on the effect of substrate(s) binding. 167 11

The progress of research in the Central Nervous System (CNS) had led to the consideration of neurons and glia as indissociable functional complexes. Neuron-glia interactions are essential for the maturation of the CNS. Glial cells release trophic factors for neurons (NGF) and neurons release trophic factors for glia (GGF). Furthermore, the latter provide a substrate for the migration of neurons and guidance of axons by mean of adhesion molecules. In adults, the interactions between neurons and glial cells serve to maintain homeostasis. Thus, the glial cells perform the restoration of the metabolic equilibrium overthrown by the transmission of the nerve impulse and provide the glucose required for neuronal activity. The nerve impulse provokes increases in the cellular space of CO2, K+, NH3 and neurotransmitters which must be taken up to allow neuronal activity to continue (in normal conditions). Astrocytes perform the uptake of the extracellular K+ by means of passive ionic channels, ionic voltage-dependent channels and a sodium-potassium-ATPase-dependent pump. The oligodendrocytes are involved in the metabolism of CO2 by converting CO2 into carbonic acid by means of carbonic anhydrase. Oligodendrocytes and astrocytes play a role in terminating neural transmission by the uptake of the amino acid neurotransmitters, such as GABA, glutamate and aspartate. The catabolism of glutamate to glutamine by means of glutamine synthetase allows both the conversion of an excitatory amino acid into a neutral amino acid (which can diffuse in the extracellular space without causing neural transmission) and the reduction of cerebral NH3 content.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Neuron-glia interactions]. 178 93

This study has dealt with the inhibition by lead of glutamine synthetase (GS) activity in homogenates of mixed glial primary cultures, 95% enriched in differentiating astrocytes. A 70% inhibition was observed with a lead concentration of only 2.5 microM. Prevention of the inhibition by addition of EDTA or dithiothreitol is compatible with the conclusion that the effect is mediated by binding of lead ion to sulfhydryl moieties of the enzyme. Among several other cations tested, only mercury, which has a similarly high binding affinity for sulfhydryl moieties, inhibited the enzyme. The inhibitory effect of lead was relatively specific, since no inhibition of another astrocytic marker enzyme, lactate dehydrogenase, of the oligodendroglial marker enzyme, 2',3'-cyclic nucleotide 3'-phosphohydrolase, or of the plasma membrane marker, Na,Ka-ATPase, was observed with concentrations of lead that produced a 70% decrease of GS. Because of the critical role of GS in regulation of extracellular glutamate, the findings raise the possibility that glutamate-induced neuronal injury is involved in the genesis of the cognitive defects associated with chronic low-level lead exposure in young children.
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PMID:Glutamine synthetase activity of developing astrocytes is inhibited in vitro by very low concentrations of lead. 197 58

Two transgenic tobacco lines were genetically engineered to contain chimaeric genes encoding the glutamine synthetase (GS) gamma polypeptide of Phaseolus vulgaris (French bean), expressed from the cauliflower mosaic virus 35S promoter. One (MIT-1) contained two copies of a construct including the first 60 amino acids of the Nicotiana plumbaginifolia beta-F1 ATPase to target the GS polypeptide to the mitochondrion. The other (CYT-4) contained a single copy of a cytosolic GS construct. Leaves of in vitro plantlets expressed the constructs and contained a novel GS polypeptide, which assembled into active GS isoenzymes constituting about 25% of the total GS activity. In in vitro plantlets of MIT-1, but not CYT-4, the novel polypeptide was found to be associated with the mitochondria. Moreover in MIT-1, the size of the novel polypeptide was not that predicted of the precursor (44.9 kDa) but was about 39 kDa, the same size as the authentic GS gamma polypeptide in CYT-4. These results are consistent with the precursor being imported into the mitochondria and cleaved near the fusion junction between the two sequences. These experiments have therefore shown that the presequence of the beta-F1 ATPase has successfully targeted the GS gamma polypeptide to the mitochondria of transgenic tobacco where it has assembled into an active isoenzyme. However, in fully regenerated plants growing photoautotrophically in growth-room conditions, although the constructs were still expressed, the gamma polypeptide did not accumulate to the same levels as in in vitro plantlets and new isoenzyme activities were now barely detectable. Moreover in leaves of the mature MIT-1 plants, the gamma polypeptide was found to be associated with the insoluble fraction of the mitochondria. The results of these experiments are discussed.
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PMID:Targeting of glutamine synthetase to the mitochondria of transgenic tobacco. 198 2

Maternal alcohol consumption produces various abnormalities in the offspring, termed fetal alcohol syndrome. We investigated various biochemical modifications occurring in the brain and the liver of pups born to alcohol-consuming rats. The parameters analysed were: superoxide dismutase, a protector against free radicals injury, enolase isoenzymes as markers of nerve cell maturation, glutamine synthetase involved in ammonia detoxification, alcohol and aldehyde deshydrogenases in order to evaluate the contribution of acetaldehyde teratogenicity and ATPase activities involved in ion and neurotransmitter transport. Activities of all these enzymes were decreased in the brain even when alcohol was withdrawn from the mother diet either during pregnancy or lactation. Activities were also decreased in the liver, except enolase and alcohol deshydrogenase activities, which were increased, suggesting possible adaptative events in the presence of alcohol. It seems likely that the multiple alterations observed in experimental fetal alcohol syndrome may be caused by free radicals following decreased superoxide dismutase activity in addition to the toxicity of alcohol and its metabolites.
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PMID:An experimental study of fetal alcohol syndrome in the rat: biochemical modifications in brain and liver. 256 12


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