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)

Using an Agrobacterium-mediated transformation system, we have introduced the intact gene of maize phosphoenolpyruvate carboxylase (PEPC), which catalyzes the initial fixation of atmospheric CO2 in C4 plants into the C3 crop rice. Most transgenic rice plants showed high-level expression of the maize gene; the activities of PEPC in leaves of some transgenic plants were two- to threefold higher than those in maize, and the enzyme accounted for up to 12% of the total leaf soluble protein. RNA gel blot and Southern blot analyses showed that the level of expression of the maize PEPC in transgenic rice plants correlated with the amount of transcript and the copy number of the inserted maize gene. Physiologically, the transgenic plants exhibited reduced O2 inhibition of photosynthesis and photosynthetic rates comparable to those of untransformed plants. The results demonstrate a successful strategy for installing the key biochemical component of the C4 pathway of photosynthesis in C3 plants.
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PMID:High-level expression of maize phosphoenolpyruvate carboxylase in transgenic rice plants. 992 Feb 61

The pathway of autotrophic CO2 fixation was studied in the phototrophic bacterium Chloroflexus aurantiacus and in the aerobic thermoacidophilic archaeon Metallosphaera sedula. In both organisms, none of the key enzymes of the reductive pentose phosphate cycle, the reductive citric acid cycle, and the reductive acetyl coenzyme A (acetyl-CoA) pathway were detectable. However, cells contained the biotin-dependent acetyl-CoA carboxylase and propionyl-CoA carboxylase as well as phosphoenolpyruvate carboxylase. The specific enzyme activities of the carboxylases were high enough to explain the autotrophic growth rate via the 3-hydroxypropionate cycle. Extracts catalyzed the CO2-, MgATP-, and NADPH-dependent conversion of acetyl-CoA to 3-hydroxypropionate via malonyl-CoA and the conversion of this intermediate to succinate via propionyl-CoA. The labelled intermediates were detected in vitro with either 14CO2 or [14C]acetyl-CoA as precursor. These reactions are part of the 3-hydroxypropionate cycle, the autotrophic pathway proposed for C. aurantiacus. The investigation was extended to the autotrophic archaea Sulfolobus metallicus and Acidianus infernus, which showed acetyl-CoA and propionyl-CoA carboxylase activities in extracts of autotrophically grown cells. Acetyl-CoA carboxylase activity is unexpected in archaea since they do not contain fatty acids in their membranes. These aerobic archaea, as well as C. aurantiacus, were screened for biotin-containing proteins by the avidin-peroxidase test. They contained large amounts of a small biotin-carrying protein, which is most likely part of the acetyl-CoA and propionyl-CoA carboxylases. Other archaea reported to use one of the other known autotrophic pathways lacked such small biotin-containing proteins. These findings suggest that the aerobic autotrophic archaea M. sedula, S. metallicus, and A. infernus use a yet-to-be-defined 3-hydroxypropionate cycle for their autotrophic growth. Acetyl-CoA carboxylase and propionyl-CoA carboxylase are proposed to be the main CO2 fixation enzymes, and phosphoenolpyruvate carboxylase may have an anaplerotic function. The results also provide further support for the occurrence of the 3-hydroxypropionate cycle in C. aurantiacus.
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PMID:Presence of acetyl coenzyme A (CoA) carboxylase and propionyl-CoA carboxylase in autotrophic Crenarchaeota and indication for operation of a 3-hydroxypropionate cycle in autotrophic carbon fixation. 997 33

White lupin (Lupinus albus L.) was grown in hydroponic culture with 1 &mgr;M phosphorus to enable the development of proteoid roots to be observed in conjunction with organic acid exudation. Discrete regions of closely spaced, determinate secondary laterals (proteoid rootlets) emerged in near synchrony on the same plant. One day after reaching their final length (4 mm), citrate exudation occurred over a 3-d pulse. The rate of exudation varied diurnally, with maximal rates during the photoperiod. At the onset of citrate efflux, rootlets had exhausted their apical meristems and had differentiated root hairs and vascular tissues along their lengths. Neither in vitro phosphoenolpyruvate carboxylase nor citrate synthase activity was correlated with the rate of citrate exudation. We suggest that an unidentified transport process, presumably at the plasma membrane, regulates citrate efflux. Growth with elevated (700 &mgr;L L-1) atmospheric [CO2] promoted earlier onset of rootlet determinacy by 1 d, resulting in shorter rootlets and citrate export beginning 1 d earlier as a 2-d diurnal pulse. Citrate was the dominant organic acid exported, and neither the rate of exudation per unit length of root nor the composition of exudate was altered by atmospheric [CO2].
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PMID:Linking development and determinacy with organic acid efflux from proteoid roots of white lupin grown with low phosphorus and ambient or elevated atmospheric CO2 concentration 1039 5

A full-length cDNA clone encoding carbonic anhydrase (CA) was isolated from a soybean nodule cDNA library. In situ hybridization and immunolocalization were performed in order to assess the location of CA transcripts and protein in developing soybean nodules. CA transcripts and protein were present at high levels in all cell types of young nodules, whereas in mature nodules they were absent from the central tissue and were concentrated in cortical cells. The results suggested that, in the earlier stages of nodule development, CA might facilitate the recycling of CO2 while at later stages it may facilitate the diffusion of CO2 out of the nodule system. In parallel, sucrose metabolism was investigated by examination of the temporal and spatial transcript accumulation of sucrose synthase (SS) and phosphoenolpyruvate carboxylase (PEPC) genes, with in situ hybridization. In young nodules, high levels of SS gene transcripts were found in the central tissue as well as in the parenchymateous cells and the vascular bundles, while in mature nodules the levels of SS gene transcripts were much lower, with the majority of the transcripts located in the parenchyma and the pericycle cells of the vascular bundles. High levels of expression of PEPC gene transcripts were found in mature nodules, in almost all cell types, while in young nodules lower levels of transcripts were detected, with the majority of them located in parenchymateous cells as well as in the vascular bundles. These data suggest that breakdown of sucrose may take place in different sites during nodule development.
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PMID:Carbon metabolism in developing soybean root nodules: the role of carbonic anhydrase. 1065 81

To clarify the pathway and role of malate synthesis in guard cells, epidermal strips isolated from Vicia faba L. leaflets were treated with 3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate (DCDP), a specific inhibitor of phosphoenolpyruvate carboxylase (PEPC). When dark-closed stomata were illuminated, malate accumulated in guard cells and stomata opened; these were inhibited by 60% and 30%, respectively, by 5 mM DCDP treatment. When light-opened stomata were treated with DCDP, both malate level in guard cells and stomatal aperture decreased. Treatment with 5 mM DCDP partially inhibited CO2 incorporation into malate in guard cells. Treatment with mannitol at 0.4 M (osmotic stress) in the light increased malate level in guard cells and closed stomata. DCDP treatment decreased both malate level and stomatal aperture under stressed condition. These results show that malate synthesis in the light under both non-stressed and stressed conditions is dependent on PEPC activity. The extent of the decrease in malate level by DCDP treatment was larger under stressed condition than under nonstressed condition, suggesting that osmotic stress may enhance the activity of this pathway of malate synthesis which is induced by light. Role of malate synthesis in guard cells is discussed.
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PMID:Role of malate synthesis mediated by phosphoenolpyruvate carboxylase in guard cells in the regulation of stomatal movement. 1075 Jul 3

The activities of carbon metabolism enzymes were determined in cellular extracts of the moderately thermophilic, chemolithotrophic, acidophilic bacterium Sulfobacillus thermosulfidooxidans subsp. asporogenes, strain 41, grown either at an atmospheric content of CO2 in the gas phase (autotrophically, heterotrophically, or mixotrophically) or autotrophically at a CO2 content increased to 5-10%. Regardless of the growth conditions, all TCA cycle enzymes (except for 2-oxoglutarate dehydrogenase), one glyoxylate cycle enzyme (malate synthase), and some carboxylases (ribulose bisphosphate carboxylase, pyruvate carboxylase, and phosphoenolpyruvate carboxylase) were detected in the cellular extracts of strain 41. During autotrophic cultivation of strains 41 and 1269, the increase in the CO2 content of the supplied air to 5-10% resulted in the activation of growth and iron oxidation, a 20-30% increase in the cellular content of protein, enhanced activity of the key TCA enzymes (citrate synthase and aconitase), and, in strain 41, a decrease in the activity of carboxylases.
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PMID:[Carbon metabolism in Sulfobacillus thermosulfidooxidans subsp. asporogenes, strain 41]. 1092 Aug 1

Capacities of phosphoenolpyruvate carboxylase (PEP-Co), ribulose bisphosphate carboxylase (Rubisco), NADP+ malic enzyme (ME) and of malate dehydrogenase (MDH) were measured in the Euphorbiacea Aleurites montana, grown under 700 ppm CO2 for four weeks prior to enzyme extraction. For comparison Bryophyllum daigremontiana (CAM). Saccharum officinarum (C4) and Capsicum frutescens (C3) were treated in the same way. PEP-Co capacity of Aleurites was in the range of 12-, that of Capsicum approx. 26 nmol x min(-1) x mg protein(-1), without significant influence of the light period or CO2-treatment. In contrast, the activity of the enzyme from Saccharum was, depending on the duration of light, 160- respectively 96 times higher than that of the tung-oil tree. In Bryophyllum a rather low activity in the morning was increased during the day to approx. 230 nmol x min(-1) x mg protein(-1) in plants grown in the greenhouse and to approx. 115 nmol x min(-1) x mg protein(-1) in those from the growth chamber. Malate was hardly detectable in extracts of Aleurites, whereas it was high in Bryophyllum, depending on the light period. The ratio of average PEP-Co to Rub-Co capacity was high for the CAM-plant (20:1), somewhat lower for sugar cane (10:1), but almost at equality for Aleurites (0.9:1) and chilli (0.8:1). For the NADP+ malic enzyme, low capacity (20 to 28 nmol x min(-1) x mg protein(-1)) was found for Aleurites and for Capsicum, whereas it was 10 to 17 times higher in Saccharum. In Bryophyllum, the activity was up to 80 nmol x min(-1) x mg protein, dependent on light period. MDH capacity was extremely high in all plants investigated. Highest rates (10-20 micromol x min(-1) x mg protein(-1)), were obtained for Bryophyllum, followed by sugar cane and Capsicum with 5-8 micromol x min(-1) x mg protein(-1). Again, the lowest capacity was found in extracts of Aleurites with approx. 1.3 to 1.6 micromol x min(-1) x m protein(-1). Thus, in Aleurites montana no indication for C4- or Crassulacean acid metabolism was obtained. Therefore, the earlier observed very efficient uptake of CO2 cannot be explained by a high expression of the PEP-Co protein, known to occur in CAM- and C4-plants.
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PMID:Capacity of enzymes of the euphorbiacea Aleurites montana involved in CO2-fixation, compared to plants having C3-, C4- and Crassulacean acid metabolism. 1092 49

Heterozygous mutants of Amaranthus edulis deficient in PEP carboxylase (PEPC) have been used to study the control of photosynthetic carbon assimilation. A reduction in PEPC activity led to a decrease in the initial slope of the relationship between the CO2 assimilation rate and the intercellular CO2 concentration and to a decrease in photosynthesis at high light intensities, consistent with a decrease in the capacity of the C4 cycle in high light. PEPC exerted appreciable control on photosynthetic flux in the wild-type, with a relatively high flux control coefficient of 0.35 in saturating light and ambient CO2. The flux control coefficient was decreased in low light or increased in low CO2 or in plants containing lower PEPC activity. However, the rate of CO2 assimilation decreased down to about 55% PEPC, followed by an up-turn in the light-saturated photosynthetic rate as PEPC was further reduced, suggesting the existence of a mechanism that compensates for the loss of PEPC activity. The amounts of photosynthetic metabolites, including glycine and serine, also showed a biphasic response to decreasing PEPC. There was a linear relationship between the activity of PEPC and the activation state of the enzyme. A possible mechanism of compensation involving photorespiratory intermediates is discussed.
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PMID:Control of C4 photosynthesis: effects of reduced activities of phosphoenolpyruvate carboxylase on CO2 assimilation in Amaranthus edulis L. 1093 41

From the initial discovery of free-running endogenous circadian oscillations of Crassulacean acid metabolism (CAM) under constant conditions in the light and in air, it has been disputed whether the underlying oscillator is enzymic or biophysical. The hypothesis of a biophysical hysteresis switch or beat oscillator started from osmotic considerations of malate accumulation and remobilisation, indicating a tonoplast tension/relaxation mechanism. It then advanced to application of non-linear dynamics theory for the analysis of rhythmic and arrhythmic time series of CO2 exchange under the regime of external control parameters, mainly temperature, and the implementation of models for computer simulations of CAM rhythms. This provided strong evidence for the tonoplast functioning as a master switch for circadian regulation of CAM. Conversely, the hypothesis of an enzymic beat oscillator strongly developed on the experimental basis of phosphorylation/dephosphorylation of phosphoenolpyruvate carboxylase (PEPC) regulating the enzyme activity, and hence CO2 fixation and malate synthesis via this enzyme. It was much supported by the discovery that PEPC-kinase gene-transcription was under circadian control. However, biochemical and molecular analysis, as well as model simulation, strongly suggests that this is a secondary and not the primary oscillator. The synchronisation/desynchronisation of leaf patches has revealed spatiotemporal characteristics of circadian rhythmicity that may open new ways for understanding biological clocks.
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PMID:The tonoplast functioning as the master switch for circadian regulation of crassulacean acid metabolism. 1114 60

The enzyme phosphoenolpyruvate carboxykinase (PEPCK) catalyzes the reversible conversion of oxalacetate and GTP to phosphoenolpyruvate (PEP), GDP, and CO2. PEPCK from higher organisms is a monomer, specifically requires GTP or ITP, and uses Mn2+ as the activating cation. Currently, there is no crystal structure of GTP-utilizing PEPCKs. The conformation of the bound nucleotide was determined from transferred nuclear Overhauser effects (trnOe) experiments to determine internuclear proton distances. At 600 MHz in the presence of PEPCK, nOe effects were observed between nucleotide protons. Internuclear distances were calculated from the initial rate of the nOe buildup. These distance constraints were used in energy minimization calculations to determine the conformation of PEPCK-bound GTP. The bound nucleotide has the base oriented anti to the C2'-endo(2E) ribose ring conformation. Relaxation rate studies indicate that there is an additional relaxation effect on the C1' proton upon nucleotide binding to PEPCK. Nucleotide binding to PEPCK-Mn2+ was studied by 1H relaxation rate studies, but results were complicated by long dipole-dipole distances and the presence of competing complexes. Modification of PEPCK by iodoacetamido-TEMPO leads to an inactive enzyme that is spin-labeled at cys273. The interaction of TEMPO-PEPCK with GTP allows for the measurement of nuclear distances between GTP and the spin label. The results suggest that cys273 lies near the ribose ring of the bound nucleotide, but it is too far to be implicated in direct hydrogen bonding interactions consistent with previous results [Makinen, A. L., and Nowak, T. J. Biol. Chem. (1989) 264, 12148], suggesting that cys273 does not actively participate in catalysis. Modification of PEPCK with several cysteine specific modifying agents causes no change in the ability of the enzyme to bind nucleotide as monitored by fluorescence quenching. A correlation between the size of the modifying agent and the maximal observed quenching upon saturation of the enzyme with nucleotide is observed. This suggests a mechanism for inactivation of PEPCK by cysteine modification due to inhibition of a dynamic motion that may occur upon nucleotide binding.
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PMID:Structural investigation of the binding of nucleotide to phosphoenolpyruvate carboxykinase by NMR. 1155 Dec


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