Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q07644 (polypeptide)
 72,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of nitrate application on glutamine synthetase activity in roots of pea (Pisum sativum L.) seedlings (2 weeks old) was studied. Separation of organelles from root fragments by sucrose density-gradient centrifugation revealed that both nitrite reductase and glutamine synthetase activities increased in root plastids as a response to nitrate application and that no such response was induced by ammonium application. Glutamine synthetase activity was also found to increase in plastids with distance from apex in nitrate-treated plants, the highest specific activity being located in the fourth 1-centimeter segment. Separation by SDS-PAGE and characterization by Western blotting showed that cytosolic glutamine synthetase contains one subunit polypeptide (28 kilodaltons) and that plastid glutamine synthetase contains both the 38-kilodalton subunit and a heavier subunit. When nitrate was present in the nutrient solution, the heavier subunit increased in abundance in protein fractions obtained from purified root plastids.
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PMID:Tissue and Cellular Distribution of Glutamine Synthetase in Roots of Pea (Pisum sativum) Seedlings. 1666 62

Glutamine synthetase from bean nodules can be separated into two isoforms, GS(n1) and GS(n2). A purification protocol has been developed. It included protamine sulfate precipitation, ammonium sulfate fractionation, anthranilate-affinity chromatography, Dye-Matrex (Orange A) chromatography, and diethylaminoethyl-cellulose ion-exchange chromatography. GS(n1) and GS(n2) have been purified to homogeneity. Subunit structure analysis using two-dimensional polyacrylamide gel electrophoresis revealed that GS(n1) was composed of two different types of subunit polypeptides. They differed in isoelectric points (6.0 and 6.3) but had the same molecular weights (46,000 Daltons). GS(n2) was composed of only one type of subunit polypeptide. It had an isoelectric point of 6.0 and a molecular weight of 46,000 Daltons. It was apparently identical to one of the polypeptides found in GS(n1). Glutamine synthetase holoenzyme consisted of eight subunits. In the nodule there are two different types of glutamine synthetase subunit polypeptides. Random combinations of the polypeptides should generate nine different isozymes. Our electrophoretic analysis revealed that GS(n2) was but one of the isozymes, and GS(n1) was a composite of the other eight. Hence, nodule glutamine synthetase isozymes were homo-octameric as well as hetero-octameric.
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PMID:Subunit Composition of Glutamine Synthetase Isozymes from Root Nodules of Bean (Phaseolus vulgaris L.). 1666 11

Changes in the levels of cytosolic glutamine synthetase (GS1) and chloroplastic glutamine synthetase (GS2) polypeptides and of corresponding mRNAs were determined in leaves of hydroponically grown rice (Oryza sativa) plants during natural senescence. The plants were grown in the greenhouse for 105 days at which time the thirteenth leaf was fully expanded. This was counted as zero time for senescence of the twelfth leaf. The twelfth leaf blade on the main stem was analyzed over a time period of -7 days (98 days after germination) to +42 days (147 days after germination). Total GS activity declined to less than a quarter of its initial level during the senescence for 35 days and this decline was mainly caused by a decrease in the amount of GS2 polypeptide. Immunoblotting analyses showed that contents of other chloroplastic enzymes, such as ribulose-1,5-bisphosphate carboxylase/oxygenase and Fd-glutamate synthase, declined in parallel with GS2. In contrast, the GS1 polypeptide remained constant throughout the senescence period. Translatable mRNA for GS1 increased about fourfold during the senescence for 35 days. During senescence, there was a marked decrease in content of glutamate (to about one-sixth of the zero time value); glutamate is the major form of free amino acid in rice leaves. Glutamine, the major transported amino acid, increased about threefold compared to the early phase of the harvest in the senescing rice leaf blades. These observations suggest that GS1 in senescing leaf blades is responsible for the synthesis of glutamine, which is then transferred to the growing tissues in rice plants.
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PMID:A Role for Glutamine Synthetase in the Remobilization of Leaf Nitrogen during Natural Senescence in Rice Leaves. 1666 1

Nodulated bean (Phaseolus vulgaris) plants were grown for 17 days after infection in normal (0.02%) CO(2) and from day 8 to 17 in high (0.1%) CO(2) in order to increase nitrogen fixation and define how nodule glutamine synthetase (GS) isoforms are regulated by the ammonia derived from the bacteroid. Nitrogenase activity was detected by day 10, and by day 17 activity was over twofold higher in 0.1% of CO(2) compared with plants grown in 0.02% CO(2) and inoculated with Rhizobium wild-type strain CE3. Likewise, plant fresh weight increased in response to increased CO(2), particularly in plants inoculated with the Rhizobium phaseoli mutant strain CFN037. Glutamine synthetase specific activity increased 2.5- to 6.5-fold from day 11 to 17. However, increased CO(2) did not appear to have an effect on GS specific activity. Analysis of the nodule GS polypeptide composition revealed that the gamma polypeptide was significantly reduced in response to high CO(2), whereas the beta polypeptide was not affected. The significance of this result in relation to the regulation of GS isoforms and their role in the assimilation of ammonia in the nodule is discussed in this paper.
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PMID:Regulation of Nodule Glutamine Synthetase by CO(2) Levels in Bean (Phaseolus vulgaris L.). 1666 81

Changes in the levels of cytosolic glutamine synthetase (GS1) and chloroplastic glutamine synthetase (GS2) polypeptides and of their corresponding mRNAs have been investigated in segments of the 13th leaf of hydroponically grown rice (Oryza sativa L.) plants during natural senescence. The leaf blade on the main stem at early (0 day), middle (15 days), and late (25 days) stages of senescence was harvested and cut into 18 or 19 segments, 2 centimeters in length from the base to the tip. The amount of GS1 polypeptide, detected with specific antibody for the GS1, was greatest near the middle of the leaf blade (segments 11-13). There was little difference in the GS1 content between corresponding leaf segments obtained at the early and middle stages of senescence. At the late senescence stage, all segments had lost some GS1 polypeptide, but more than 50% of GS1 detected at both the early and middle stages was still detectable in segments. The relative content of mRNA for GS1 in the total RNA in all segments was very low during early senescence but increased in all leaf segments during later senescence. At the late stage of senescence, GS1 mRNA in the total RNA increased about 4.2- to 4.6-fold in segments 12 to 16 in the day-25 samples compared with those in the early stage. The content of the GS2 polypeptide, as well as ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) protein, was highest in segment 17 in the 0-day samples. During senescence, this peak became lower and broader, and finally disappeared, i.e. approximately 80% of GS2 polypeptide and Rubisco protein in segment 17 were lost by day 25. In contrast with GS2 polypeptide, the relative level of GS2 mRNA increased 1.8- to 2.9-fold in individual segments at the middle stage of senescence. Even at the late stage, the transcript signals remained slightly higher than those at the early stage in all segments. Thus, GS1 and GS2 polypeptides and corresponding mRNAs responded in a different manner within an attached rice leaf during natural senescence. The contents of GS1 and GS2 polypeptides were not simply determined by the abundance of their corresponding mRNAs in the rice leaf blades during natural senescence.
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PMID:Changes in Cytosolic Glutamine Synthetase Polypeptide and its mRNA in a Leaf Blade of Rice Plants during Natural Senescence. 1666 95

The small GstI protein (63 amino acids) of Rhizobium leguminosarum is the endogenous inhibitor of the glnII (glutamine synthetase II) gene expression. It has been suggested that GstI has a predominantly beta-structure and mediates the block of translation and stabilization of glnII mRNA through direct binding to its 5' untranslated region. Because of the unavailability of adequate amounts of purified recombinant protein, the mechanism as well as the protein tridimensional structure remain very poorly understood. To obtain the full-length protein, we have undertaken the chemical synthesis of the protein by different approaches. In a first attempt, the stepwise synthesis was unsuccessful, with strong aggregation experienced on the N-terminal side, after residue 44 from the C-terminus. In a second approach, we set up the conditions to carry out a native chemical ligation (NCL). Albeit the protein contains two Cysteine residues, located at positions 40 and 47, to minimize the size of the N-terminal segment to be synthesized, we have devised an alternative strategy of ligation on Met32, utilizing homoCys as the ligating moiety and then alkylating the resulting polypeptide with methyl iodide. New conditions to quantitatively methylate thiol groups in complex polypeptides have been conceived, obtaining the protein in very good yields and purity. A CD spectroscopy investigation has revealed that the protein does not adopt canonical secondary structures but is very rich in beta-structure (approximately 60%), in agreement with a previous study carried out on samples obtained by recombinant methods.
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PMID:The chemical synthesis of the GstI protein by NCL on a X-Met site. 1688 73

Control of human visceral leishmaniasis in regions where it is endemic is hampered in part by limited accessibility to medical care and emerging drug resistance. There is no available protective vaccine. Leishmania spp. protozoa express multiple antigens recognized by the vertebrate immune system. Since there is not one immunodominant epitope recognized by most hosts, strategies must be developed to optimize selection of antigens for prevention and immunodiagnosis. For this reason, we generated a cDNA library from the intracellular amastigote form of Leishmania chagasi, the cause of South American visceral leishmaniasis. We employed a two-step expression screen of the library to systematically identify T-cell antigens and T-dependent B-cell antigens. The first step was aimed at identifying the largest possible number of clones producing an epitope-containing polypeptide by screening with a pool of sera from Brazilians with documented visceral leishmaniasis. After removal of clones encoding heat shock proteins, positive clones underwent a second-step screen for their ability to cause proliferation and gamma interferon responses in T cells from immune mice. Six unique clones were selected from the second screen for further analysis. The corresponding antigens were derived from glutamine synthetase, a transitional endoplasmic reticulum ATPase, elongation factor 1gamma, kinesin K39, repetitive protein A2, and a hypothetical conserved protein. Humans naturally infected with L. chagasi mounted both cellular and antibody responses to these proteins. Preparations containing multiple antigens may be optimal for immunodiagnosis and protective vaccines.
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PMID:Leishmania chagasi T-cell antigens identified through a double library screen. 1700 Jul 24

Lengsin (LGS) is an abundant transcript in the human lens, encoding a predicted polypeptide similar to glutamine synthetase (GS). We show that a major alternatively spliced product of LGS codes for a 57kDa polypeptide that assembles into a catalytically inactive dodecamer, cross-reacts with anti-GS antibodies, and is expressed at high levels in transparent, but not cataractous, human lenses. Based on this characteristic oligomeric organization, preferential expression in the transparent lens, and amyloid-beta association previously reported for GS, a potential chaperone-like role of LGS has been investigated. We find that LGS has six binding sites for the hydrophobic surface probe bis-ANS and relieves cellular toxicity caused by amyloid-beta expression in a folding-impaired yeast mutant. While documenting the structural similarity between LGS and prokaryotic GS-I, the data rule out any involvement of lengsin in glutamine biosynthesis and suggest an unrelated role that may be important for lens homeostasis and transparency.
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PMID:Structural and functional properties of lengsin, a pseudo-glutamine synthetase in the transparent human lens. 1701 Sep 35

Following the discovery of glutamine synthetase/glutamate (Glu) synthase, the physiological roles of Glu dehydrogenase (GDH) in nitrogen metabolism in plants remain obscure and is the subject of considerable controversy. Recently, transgenics were used to overexpress the gene encoding for the beta-subunit polypeptide of GDH, resulting in the GDH-isoenzyme 1 deaminating in vivo Glu. In this work, we present transgenic tobacco (Nicotiana tabacum) plants overexpressing the plant gdh gene encoding for the alpha-subunit polypeptide of GDH. The levels of transcript correlated well with the levels of total GDH protein, the alpha-subunit polypeptide, and the abundance of GDH-anionic isoenzymes. Assays of transgenic plant extracts revealed high in vitro aminating and low deaminating activities. However, gas chromatography/mass spectrometry analysis of the metabolic fate of (15)NH(4) or [(15)N]Glu revealed that GDH-isoenzyme 7 mostly deaminates Glu and also exhibits low ammonium assimilating activity. These and previous results firmly establish the direction of the reactions catalyzed by the anionic and cationic isoenzymes of GDH in vivo under normal growth conditions and reveal a paradox between the in vitro and in vivo enzyme activities.
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PMID:The isoenzyme 7 of tobacco NAD(H)-dependent glutamate dehydrogenase exhibits high deaminating and low aminating activities in vivo. 1793 5

Adenylyltransferase (GlnE) catalyzes the reversible adenylylation of glutamine synthetase. In this report we present, for the first time, evidence for a peroxiredoxin activity of Rhodospirillum rubrum GlnE, through the carboxyl-terminal AhpC/thiol-specific antioxidant (TSA) domain. The combination of GlnE and AhpC/TSA domains within the same polypeptide constitutes a unique domain architecture that has not previously been identified among proteobacteria.
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PMID:A novel peroxiredoxin activity is located within the C-terminal end of Rhodospirillum rubrum adenylyltransferase. 1795 75


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