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

---

Query: EC:4.1.1.32 (phosphoenolpyruvate carboxykinase)
4,204 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rats of different ages (3 to 15-wk-old) were fed on a 25% casein diet for one week, and the nitrogen balance and liver serine dehydratase (SDH, EC 4.2.1.13) activity were then determined. The value for nitrogen balance decreased with the age of the rats, while the liver SDH activity increased. A statistical analysis showed clear inverse correlation between the two factors (R(2) = 0.7372, p < 0.01). This result suggests that SDH was induced by response to the amount of surplus amino acids from dietary protein taken beyond the body's requirement. The increase in SDH activity was accompanied by an increase in the level of SDH mRNA. Since the half-life of this mRNA did not change significantly, the induction was mainly controlled at the level of transcription. In addition, the induction seems not to be related to gluconeogenesis, since the mRNA levels of tyrosine aminotransferase (TAT) and phosphoenolpyruvate carboxykinase (PEPCK), other gluconeogenic enzymes, were not changed under these experimental conditions.
...
PMID:Inverse correlation between the nitrogen balance and induction of rat liver serine dehydratase (SDH) by dietary protein. 1511 19

Understanding of the influences of root-zone CO2 concentration on nitrogen (N) metabolism is limited. The influences of root-zone CO2 concentration on growth, N uptake, N metabolism and the partitioning of root assimilated 14C were determined in tomato (Lycopersicon esculentum). Root, but not leaf, nitrate reductase activity was increased in plants supplied with increased root-zone CO2. Root phosphoenolpyruvate carboxylase activity was lower with NO3(-)- than with NH4(+)-nutrition, and in the latter, was also suppressed by increased root-zone CO2. Increased growth rate in NO3(-)-fed plants with elevated root-zone CO2 concentrations was associated with transfer of root-derived organic acids to the shoot and conversion to carbohydrates. With NH4(+)-fed plants, growth and total N were not altered by elevated root-zone CO2 concentrations, although 14C partitioning to amino acid synthesis was increased. Effects of root-zone CO2 concentration on N uptake and metabolism over longer periods (> 1 d) were probably limited by feedback inhibition. Root-derived organic acids contributed to the carbon budget of the leaves through decarboxylation of the organic acids and photosynthetic refixation of released CO2.
...
PMID:The influence of root assimilated inorganic carbon on nitrogen acquisition/assimilation and carbon partitioning. 1572 Jun 30

Levels of cytokinins and abscisic acid (ABA) and the expression of senescence-related genes were investigated in two maize (Zea mays L.) cultivars of different senescence type, cv. P3845 (stay-green) and cv. Hokkou 55 (earlier senescent), in a field study. The delay in leaf senescence in P3845 was correlated with increased levels of chlorophyll and nitrogen and a higher photon-saturated photosynthetic rate (P(sat)). Compared with the earlier senescent Hokkou 55, P3845 showed enhanced contents of cytokinins (trans-zeatin riboside, t-ZR; dihydrozeatin riboside, DHZR; isopentenyladenosine, iPA) and reduced levels of ABA in its leaves. In roots, P3845 had increased levels of t-ZR, DHZR, and ABA, but decreased concentrations of iPA. It was concluded that a higher rate of cytokinin transport from roots to leaves contributes to the delay of senescence in P3845. By contrast, the translocation of ABA from roots to shoots may be blocked in the stay-green cultivar, which also results in retarded leaf senescence. P3845 ear leaves contained more malondialdehyde (MDA) and higher catalase (CAT) and superoxide dismutase (SOD) activities than Hokkou 55. Since the accumulation of the mRNAs for Rubisco small subunit (rbcS), phosphoenolpyruvate carboxylase (PEPC), and SOD peaked after Chl content and P(sat) had reached their maxima, it is speculated that when leaf senescence is initiated, Chl contents decrease first, followed by the degradation of the photosynthetic apparatus and of photosynthesis-related enzymes. See1 and See2 encode senescence-related cysteine proteases; their mRNAs were most abundant in yellowing leaves, suggesting that these proteins are involved in the process of senescence rather than its initiation. mRNAs of both genes were more abundant in Hokkou 55 than in P3845, which suggests a regulation of leaf senescence at the transcriptional level.
...
PMID:Endogenous hormones and expression of senescence-related genes in different senescent types of maize. 1572 26

Storage protein synthesis is dependent on available nitrogen in the seed, which may be controlled by amino acid import via specific transporters. To analyze their rate-limiting role for seed protein synthesis, a Vicia faba amino acid permease, VfAAP1, has been ectopically expressed in pea (Pisum sativum) and Vicia narbonensis seeds under the control of the legumin B4 promoter. In mature seeds, starch is unchanged but total nitrogen is 10% to 25% higher, which affects mainly globulin, vicilin, and legumin, rather than albumin synthesis. Transgenic seeds in vitro take up more [14C]-glutamine, indicating increased sink strength for amino acids. In addition, more [14C] is partitioned into proteins. Levels of total free amino acids in growing seeds are unchanged but with a shift toward higher relative abundance of asparagine, aspartate, glutamine, and glutamate. Hexoses are decreased, whereas metabolites of glycolysis and the tricarboxylic acid cycle are unchanged or slightly lower. Phosphoenolpyruvate carboxylase activity and the phosphoenolpyruvate carboxylase-to-pyruvate kinase ratios are higher in seeds of one and three lines, indicating increased anaplerotic fluxes. Increases of individual seed size by 20% to 30% and of vegetative biomass indicate growth responses probably due to improved nitrogen status. However, seed yield per plant was not altered. Root application of [15N] ammonia results in significantly higher label in transgenic seeds, as well as in stems and pods, and indicates stimulation of nitrogen root uptake. In summary, VfAAP1 expression increases seed sink strength for nitrogen, improves plant nitrogen status, and leads to higher seed protein. We conclude that seed protein synthesis is nitrogen limited and that seed uptake activity for nitrogen is rate limiting for storage protein synthesis.
...
PMID:Ectopic expression of an amino acid transporter (VfAAP1) in seeds of Vicia narbonensis and pea increases storage proteins. 1579 70

The short-term effects of the herbicide glyphosate (1.25-10 mM) on the growth, nitrogen fixation, carbohydrate metabolism, and shikimate pathway were investigated in leaves and nodules of nodulated lupine plants. All glyphosate treatments decreased nitrogenase activity rapidly (24 h) after application, even at the lowest and sublethal dose used (1.25 mM). This early effect on nitrogenase could not be related to either damage to nitrogenase components (I and II) or limitation of carbohydrates supplied by the host plant. In fact, further exposure to increasing glyphosate concentrations (5 mM) and greater time after exposure (5 days) decreased nodule starch content and sucrose synthase (SS; EC 2.4.1.13) activity but increased sucrose content within the nodule. These effects were accompanied by a great inhibition of the activity of phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31). There were remarkable and rapid effects on the increase of shikimic and protocatechuic (PCA) acids in nodules and leaves after herbicide application. On the basis of the role of shikimic acid and PCA in the regulation of PEPC, as potent competitive inhibitors, this additional effect provoked by glyphosate on 5-enolpyruvylshikimic-3-phosphate synthase enzyme (EPSPS; EC 2.5.1.19) inhibition would divert most PEP into the shikimate pathway, depriving energy substrates to bacteroids to maintain nitrogen fixation. These findings provide a new explanation for the effectiveness of glyphosate as a herbicide in other plant tissues, for the observed differences in tolerance among species or cultivars, and for the transitory effects on glyphosate-resistant transgenic crops under several environmental conditions.
...
PMID:New insights on glyphosate mode of action in nodular metabolism: Role of shikimate accumulation. 1656 53

Previous studies with intact maize (Zea mays L.) plants indicated that phosphoenolpyruvate carboxylase (PEPC) levels are controlled by nitrogen (N) availability and that this regulation is presumably at the transcriptional level (B. Sugiharto, K. Miyata, H. Nakamoto, H. Sasakawa, T. Sugiyama [1990] Plant Physiol 92: 963-969; B. Sugiharto, T. Sugiyama [1992] Plant Physiol 98: 1403-1408). In the present study, detached maize leaves were used to investigate further the mechanism of N-dependent regulation of gene expression in C(4) plants. PEPC and carbonic anhydrase (CA) mRNA levels decreased in leaves detached from maize plants. Addition of high nitrate did not prevent this decrease. However, the addition of zeatin to solutions bathing the cut ends of the detached leaves inhibited the decrease of PEPC and CA mRNA levels. Simultaneous addition of high nitrate and zeatin to leaves detached from N-deficient maize plants caused a large and rapid increase in PEPC and CA mRNA levels. Zeatin could be replaced by benzyladenine, but not by indoleacetic acid or abscisic acid. Both CA isozymes were effected and responded in an identical manner. We conclude that detached maize leaves provide an excellent experimental system to study the mechanism(s) of N-mediated regulation of PEPC and CA gene expression. However, zeatin is an essential component of this system.
...
PMID:Cytokinin Is Required to Induce the Nitrogen-Dependent Accumulation of mRNAs for Phosphoenolpyruvate Carboxylase and Carbonic Anhydrase in Detached Maize Leaves. 1665 38

The regulation of carbon partitioning between carbohydrates (principally sucrose) and amino acids has been only poorly characterized in higher plants. The hypothesis that the pathway of sucrose and amino acid biosynthesis compete for carbon skeletons and energy is widely accepted. In this review, we suggest a mechanism involving the regulation of cytosolic protein kinases whereby the flow of carbon is regulated at the level of partitioning between the pathways of carbohydrate and nitrogen metabolism via the covalent modulation of component enzymes. The addition of nitrate to wheat seedlings (Triticum aestivum) grown in the absence of exogenous nitrogen has a dramatic, if transient, impact on sucrose formation and on the activities of sucrose phosphate synthase (which is inactivated) and phosphoenolpyruvate carboxylase (which is activated). The activities of these two enzymes are modulated by protein phosphorylation in response to the addition of nitrate, but they respond in an inverse fashion. Sucrose phosphate synthase in inactivated and phosphoenolpyruvate carboxylase is activated. Nitrate functions as a signal metabolite activating the cytosolic protein kinase, thereby modulating the activities of at least two of the key enzymes in assimilate partitioning and redirecting the flow of carbon away from sucrose biosynthesis toward amino acid synthesis.
...
PMID:Nitrate activation of cytosolic protein kinases diverts photosynthetic carbon from sucrose to amino Acid biosynthesis: basis for a new concept. 1665 3

Intercellular distribution of enzymes involved in amino nitrogen synthesis was studied in leaves of species representing three C(4) groups, i.e. Sorghum bicolor, Zea mays, Digitaria sanguinalis (NADP malic enzyme type); Panicum miliaceum (NAD malic enzyme type); and Panicum maximum (phosphoenolpyruvate carboxykinase type). Nitrate reductase, nitrite reductase, glutamine synthetase, and glutamate synthase were predominantly localized in mesophyll cells of all the species, except in P. maximum where nitrite reductase had similar activity on a chlorophyll basis, in both mesophyll and bundle sheath cells. NADH-glutamate dehydrogenase was concentrated in the bundle sheath cells, while NADPH-glutamate dehydrogenase was localized in both mesophyll and bundle sheath cells. The activities of nitrate-assimilating enzymes, except for nitrate reductase, were high enough to account for the proposed in vivo rates of nitrate assimilation.Based on the differential centrifugation of cell homogenates of P. miliaceum, mesophyll chloroplasts appear to be the major site of nitrate assimilation since nitrite reductase, glutamine synthetase, glutamate synthase, and NADPH-glutamate dehydrogenase were primarily localized in the chloroplast fraction. Both the glutamine synthetase-glutamate synthase and glutamate dehydrogenase pathways were considered as alternative routes of amino nitrogen synthesis.
...
PMID:Distribution of Nitrate-assimilating Enzymes between Mesophyll Protoplasts and Bundle Sheath Cells in Leaves of Three Groups of C(4) Plants. 1665 90

Labeling studies using detached lupin (Lupinus angustifolius) nodules showed that over times of less than 3 minutes, label from [3,4-(14)C]glucose was incorporated into amino acids, predominantly aspartic acid, to a much greater extent than into organic acids. Only a slight preferential incorporation was observed with [1-(14)C]- and [6-(14)C]glucose, while with [U-(14)C]-glucose more label was incorporated into organic acids than into amino acids at all labeling times. These results are consistent with a scheme whereby the "carbon skeletons" for amino acid synthesis are provided by the phosphoenolpyruvate carboxylase reaction.A comparison of (14)CO(2) release from nodules supplied with [1-(14)C]- and [6-(14)C]glucose indicated that the oxidative pentose phosphate pathway accounted for less than 6% of glucose metabolism. Several enzymes of the oxidative pentose phosphate and glycolytic pathways were assayed in vitro using the 12,000g supernatant fraction from nodule homogenates. In all cases, the specific activities were adequate to account for the calculated in vivo fluxes.Three out of four diverse treatments that inhibited nodule nitrogen fixation also inhibited nodule CO(2) fixation, and in the case of the fourth treatment, replacement of N(2) with He, it was shown that the normal entry of label from exogenous (14)CO(2) into the nodule amino acid pool was strongly inhibited.
...
PMID:Carbon Dioxide Fixation by Lupin Root Nodules: II. Studies with C-labeled Glucose, the Pathway of Glucose Catabolism, and the Effects of Some Treatments That Inhibit Nitrogen Fixation. 1666 Jul 46

Nitrogen assimilation in crabgrass Digitaria sanguinalis (L.) Scop., was studied by comparing leaf extracts with isolated mesophyll cell and bundle sheath strand extracts. The results show that both nitrate and nitrate reductase are localized in mesophyll cells; glutamine synthetase is nearly equally distributed in the mesophyll and bundle sheath; approximately 67% of the glutamate synthase activity is in the bundle sheath and 33% is in the mesophyll; and 80% of the glutamate dehydrogenase activity is in the bundle sheath, with the NADH-dependent form exhibiting a 2.5-fold higher activity than the NADPH-dependent form.Isolated crabgrass mesophyll cells reduce NO(2) (-) coupled to the photochemical production of O(2) but are inactive with NO(3) (-). The NO(2) (-) -dependent O(2) evolution is light-dependent; inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea; stimulated by photophosphorylation uncouplers; and exhibits a stoichiometry of O(2) evolved to NO(2) (-) reduced of 1.45 and 0.67 in coupled and uncoupled experiments, respectively. Isolated bundle sheath strands are inactive in O(2) evolution with NO(3) (-) or NO(2) (-).Based on these results, plus literature data, two schemes for crabgrass leaf nitrogen assimilation are presented, depending on whether the plant is using ammonium or nitrate as its nitrogen source. It is proposed that the increased nitrogen use efficiency in crabgrass and other C(4) plants is due partially to a "division of labor" between mesophyll and bundle sheath cells, where NO(3) (-) and NO(2) (-) reductase in mesophyll cells act as nitrogen reduction traps in an analogous fashion to phosphoenolpyruvate carboxylase acting as a CO(2) trap during C(4) photosynthesis.
...
PMID:Nitrogen Assimilation Pathways in Leaf Mesophyll and Bundle Sheath Cells of C(4) Photosynthesis Plants Formulated from Comparative Studies with Digitaria sanguinalis (L.) Scop. 1666 Sep 55


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---