Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.1.1.32 (phosphoenolpyruvate carboxykinase)
4,204 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:Nitrate activation of cytosolic protein kinases diverts photosynthetic carbon from sucrose to amino Acid biosynthesis: basis for a new concept. 1665 3

We have used detached leaves to study the N-dependent control of expression of phosphoenolpyruvate carboxylase (PEPC) and carbonic anhydrase (CA) genes in maize (Zea mays L. cv Golden Cross Bantam T51). Following supplementation with an N-source and zeatin, PEPC and CA mRNA levels increased in leaves detached from N-deficient maize plants. Addition of methionine sulfoximine (MSX), a specific inhibitor of glutamine synthetase, inhibited the nitrate-dependent increase of PEPC and CA mRNA but did not affect the glutamine-dependent increase of PEPC and CA mRNA levels. Glutamine levels in detached maize leaves treated with various N sources in the presence or absence of MSX correlated with the levels of PEPC and CA mRNA. We conclude that glutamine is the most likely effector for controlling the N-dependent expression of PEPC and CA in maize plants.
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PMID:Glutamine Induces the N-Dependent Accumulation of mRNAs Encoding Phosphoenolpyruvate Carboxylase and Carbonic Anhydrase in Detached Maize Leaf Tissue. 1665 41

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.
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PMID:Distribution of Nitrate-assimilating Enzymes between Mesophyll Protoplasts and Bundle Sheath Cells in Leaves of Three Groups of C(4) Plants. 1665 90

Wheat seedlings (Triticum vulgare) treated with 1 mm KNO(3) or NaNO(3), in the presence of 0.2 mm CaSO(4), were compared during a 48-hour period with respect to nitrate uptake, translocation, accumulation and reduction; cation uptake and accumulation; and malate accumulation. Seedlings treated with KNO(3) absorbed and accumulated more nitrate, had higher nitrate reductase levels in leaves but less in roots, accumulated 17 times more malate in leaves, and accumulated more of the accompanying cation than seedlings treated with NaNO(3). Within seedlings of each treatment, changes in nitrate reductase activity and malate accumulation were parallel in leaves and in roots. Despite the great difference in malate accumulation, leaves of the KNO(3)-treated seedlings had only slightly greater levels of phosphoenolpyruvate carboxylase than leaves of NaNO(3)-treated seedlings. NADP-malic enzyme levels increased only slightly in leaves and roots of both KNO(3)- and NaNO(3)-treated seedlings. The effects of K(+) and Na(+) on all of these parameters can best be explained by their effects on nitrate translocation, which in turn affects the other parameters. In a separate experiment, we confirmed that phosphoenolpyruvate carboxylase activity increased about 2-fold during 36 hours of KNO(3) treatment, and increased only slightly in the KCl control.
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PMID:Role of potassium and malate in nitrate uptake and translocation by wheat seedlings. 1666 Jun 6

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.
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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

The leaf anatomy and certain photosynthetic properties of nitrate- and ammonia-grown plants of Moricandia arvensis (L.) DC., a species previously reported to be a C(3)-C(4) intermediate, were investigated. Nitrate-grown plants had a high level of malate in the leaves while ammonia-grown plants had low levels of malate. In young leaves of nitrate-grown plants, there was a diurnal fluctuation of malate content, increasing during the day and decreasing during the night. Titratable acidity remained low in leaves of both nitrate- and ammonia-grown plants.In nitrate-grown plants, the activity of phosphoenolpyruvate (PEP) carboxylase was about 2-fold higher than in ammonia-grown plants, the latter having activity typical of C(3) species. Also, in nitrate-grown plants, the ratio of activities of ribulose 1,5-bisphosphate (RuBP) carboxylase/PEP carboxylase was lower than in ammonia-grown plants. Nitrate reductase activities were higher in nitrate- than in ammonia-grown plants and the greatest activity was found in younger leaves.With nitrate-grown plants, during a pulse-chase experiment the label in malate, as a percentage of the total labeled products, increased from about 7% after a 10-second pulse with (14)CO(2) up to 17% during a 5-minute chase with (12)CO(2). The pattern of (14)C labeling in various metabolites suggests the primary carboxylation is through RuBP carboxylase with a secondary carboxylation through PEP carboxylase. In similar experiments, with ammonia-grown plants, the percentage label in malate was only 0% to 4% with no increase in malate labeling during the chase period. The CO(2) compensation point was lower in nitrate-grown than ammonia-grown plants.There was no evidence of Kranz-like anatomy in either the nitrate or ammonia-grown plants. Mitochondria of bundle-sheath cells were strikingly positioned along the inner tangential wall. This might allow the chloroplasts of these cells to fix the mitochondrial photorespired CO(2) more effectively and contribute to the low CO(2) compensation point in the species. Chloroplasts of bundle-sheath cells and contiguous mesophyll cells were similar in size and structure in plants grown on different media, although chloroplast thylakoids and stromata of the ammonia-grown plants stained more intensely than those of nitrate-grown plants. In addition, irregular clusters of phytoferritin particles occurred in the chloroplasts of the ammonia-grown plants.The results indicate that the substantial activity of PEP carboxylase, incorporation of CO(2) into malate, the high malate content, and in part the relatively low CO(2) compensation point in Moricandia arvensis may be accounted for by metabolism of nitrate rather than by a state of C(3)-C(4) intermediacy.
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PMID:Influence of Nitrate and Ammonia on Photosynthetic Characteristics and Leaf Anatomy of Moricandia arvensis. 1666 44

Young bean plants (Phaseolus vulgaris L. var Saxa) were fed with three different types of inorganic nitrogen, after being grown on nitrogen-free nutrient solution for 8 days. The pattern of (14)CO(2) fixation was investigated in photosynthesizing primary leaf discs of 11-day-old plants (3 days with nitrogen source) and in a pulse-chase experiment in 13-day-old plants (5 days with nitrogen source).Ammonium caused, in contrast to nitrate nutrition, a higher level of (14)C incorporation into sugar phosphates but a lower incorporation of label into malate, glycolate, glycerate, aspartate, and alanine. The labeling kinetics of glycine and serine were little changed by the nitrogen source. Ammonium feeding also produced an increase in the ratio of extractable activities of ribulose-1,5-bisphosphate carboxylase to phosphoenolpyruvate carboxylase and an increase in dark respiration and the CO(2) compensation concentration. Net photosynthesis was higher in plants assimilating nitrate.The results point to stimulated turnover of the photosynthetic carbon reduction cycle metabolites, reduced phosphoenolpyruvate carboxylation, and altered turnover rates within the photosynthetic carbon oxidation cycle in ammonium-fed plants. Mechanisms of the regulation of primary carbon metabolism are proposed and discussed.
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PMID:Effects of Different Inorganic Nitrogen Sources on Photosynthetic Carbon Metabolism in Primary Leaves of Non-nodulated Phaseolus vulgaris L. 1666 66

Detached roots and nodules of the N(2)-fixing species, Albus glutinosa (European black alder), actively assimilate CO(2). The maximum rates of dark CO(2) fixation observed for detached nodules and roots were 15 and 3 micromoles CO(2) fixed per gram dry weight per hour, respectively. The net incorporation of CO(2) in these tissues was catalyzed by phosphoenolpyruvate carboxylase which produces organic acids, some of which are used in the synthesis of the amino acids, aspartate, glutamate, and citrulline and by carbamyl phosphate synthetase. The latter accounts for approximately 30 to 40% of the CO(2) fixed and provides carbamyl phosphate for the synthesis of citrulline. Results of labeling studies suggest that there are multiple pools of malate present in nodules. The major pool is apparently metabolically inactive and of unknown function while the smaller pool is rapidly utilized in the synthesis of amino acids. Dark CO(2) fixation and N(2) fixation in nodules decreased after treatment of nodulated plants with nitrate while the percentage of the total (14)C incorporated into organic acids increased. Phosphoenolpyruvate carboxylase and carbamyl phosphate synthetase play key roles in the synthesis of amino acids including citrulline and in the metabolism of N(2)-fixing nodules and roots of alder.
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PMID:Carbon Dioxide Fixation in Roots and Nodules of Alnus glutinosa: I. Role of Phosphoenolpyruvate Carboxylase and Carbamyl Phosphate Synthetase in Dark CO(2) Fixation, Citrulline Synthesis, and N(2) Fixation. 1666 82

In vivo CO(2) fixation activity and in vitro phosphoenolpyruvate carboxylase activity were demonstrated in effective and ineffective nodules of alfalfa (Medicago sativa L.) and in the nodules of four other legume species. Phosphoenolpyruvate carboxylase activity was greatly reduced in nodules from both host and bacterially conditioned ineffective alfalfa nodules as compared to effective alfalfa nodules.Forage harvest and nitrate application reduced both in vivo and in vitro CO(2) fixation activity. By day 11, forage harvest resulted in a 42% decline in in vitro nodule phosphoenolpyruvate carboxylase activity while treatment with either 40 or 80 kilograms nitrogen per hectare reduced activity by 65%. In vitro specific activity of phosphoenolpyruvate carboxylase and glutamate synthase were positively correlated with each other and both were positively correlated with acetylene reduction activity.The distribution of radioactivity in the nodules of control plants (unharvested, 0 kilograms nitrogen per hectare) averaged 73% into the organic acid and 27% into the amino acid fraction. In nodules from harvested plants treated with nitrate, near equal distribution of radioactivity was observed in the organic acid (52%) and amino acid (48%) fractions by day 8. Recovery to control distribution occurred only in those nodules whose in vitro phosphoenolpyruvate carboxylase activity recovered.The results demonstrate that CO(2) fixation is correlated with nitrogen fixation in alfalfa nodules. The maximum rate of CO(2) fixation for attached and detached alfalfa nodules at low CO(2) concentrations (0.13-0.38% CO(2)) were 18.3 and 4.9 nanomoles per hour per milligram dry weight, respectively. Nodule CO(2) fixation was estimated to provide 25% of the carbon required for assimilation of symbiotically fixed nitrogen in alfalfa.
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PMID:Alfalfa root nodule carbon dioxide fixation : I. Association with nitrogen fixation and incorporation into amino acids. 1666 26

Maize (Zea mays L. cv Golden Cross Bantam T51) seedlings were grown under full sunlight or 50% sunlight in a temperature-controlled glasshouse at the temperatures of near optimum (30/25 degrees C) and suboptimum (17/13 degrees C) with seven levels of nitrate-N (0.4 to 12 millimolars). The contents of phosphoenolpyruvate carboxylase (PEPC), pyruvate orthophosphate dikinase (PPD), and ribulose-1,5-P(2) carboxylase/oxygenase (RuBisCO) were immunochemically determined for each treatment with rabbit antibodies raised against the respective maize leaf proteins (anti-PEPC and anti-PPD) or spinach leaf protein (anti-RuBisCO). The content of each enzymic protein increased with increasing N and raised under reduced temperature. The positive effect of light intensity on their contents was evident only at near optimal temperature. The relative increase in PEPC and PPD content with increasing N was significantly greater than that of RuBisCO irrespective of growth conditions. These enzymic proteins comprised about 8, 6, and 35% of total soluble protein, respectively, at near optimal growth condition. In contrast to significant increase in the proportion of soluble protein allocated to PEPC and PPD seen under certain conditions, the proportion allocated to RuBisCO decreased reciprocally with an increased biomass yield by N supply.These results indicated that the levels of PEPC and PPD parallel to maize biomass more tightly than that of RuBisCO at least under near optimal growth condition.
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PMID:Partitioning of Nitrogen among Ribulose-1,5-bisphosphate Carboxylase/Oxygenase, Phosphoenolpyruvate Carboxylase, and Pyruvate Orthophosphate Dikinase as Related to Biomass Productivity in Maize Seedlings. 1666 84


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