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)

There is little information available on the primary products of photosynthesis and the change in the activity of the associated enzymes with altitude. We studied the same in varieties of barley and wheat grown at 1300 (low altitude, LA) and 4200 m (high altitude, HA) elevations above mean sea level in the western Himalayas. Plants at both the locations had similar photosynthetic rates, leaf water potential and the chlorophyll fluorescence kinetics. The short-term radio-labelling experiments in leaves showed appearance of (14)CO(2) in phosphoglyceric acid and sugar phosphates in plants at both the LA and HA, suggesting a major role of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in CO(2) fixation in the plants at two altitudes, whereas the appearance of labelled carbon in aspartate (Asp) and glutamate (Glu) at HA suggested a role of phosphoenolpyruvate carboxylase (PEPCase) in photosynthesis metabolism. Plants at HA had significantly higher activities of PEPCase, carboxylase and oxygenase activity of Rubisco, aspartate aminotransferase (AspAT), and glutamine synthetase (GS). However, the activities of malate dehydrogenase, NAD-malic enzyme and citrate synthase were similar at the two locations. Such an altered metabolism at HA suggested that PEPCase probably captured CO(2) directly from the atmosphere and/or that generated metabolically e.g. from photorespiration at HA. Higher oxygenase activity at HA suggests high photorespiratory activity. OAA thus produced could be additionally channelised for Asp synthesis using Glu as a source of ammonia. Higher GS activity ensures higher assimilation rate of NH(3) and the synthesis of Glu through GS-GOGAT (glutamine:2-oxoglutarate aminotransferase) pathway, also as supported by the appearance of radiolabel in Glu at HA. Enhanced PEPCase activity coupled with higher activities of AspAT and GS suggests a role in conserving C and N in the HA environment.
...
PMID:Effect of altitude on the primary products of photosynthesis and the associated enzymes in barley and wheat. 1645 48

The localization of some key enzymes leading to sucrose synthesis in photosynthetic tissue of C(3) and C(4) species was investigated. These included UDP-glucose (UDPG) pyrophosphorylase, sucrose phosphate synthetase, and glycerate kinase. Whether glycerate kinase is localized exclusively in the chloroplast or partly outside the chloroplast could influence the fate of carbon flow to sucrose through the glycolate pathway.In the C(3) species wheat, intact chloroplasts were isolated from protoplasts. Following separation of the chloroplasts by differential centrifugation and by sucrose density gradient centrifugation, UDPG pyrophosphorylase, sucrose phosphate synthetase, and sucrose synthetase were found outside the chloroplast while glycerate kinase was localized in the chloroplast.In the C(4) species (maize, NADP-malic enzyme-type; Panicum miliaceum, NAD-malic enzyme type and Brachiaria erucaeformis, phosphoenolpyruvate carboxykinase type) the distribution of UDPG pyrophosphorylase and glycerate kinase between mesophyll and bundle sheath cells and their intracellular localization in mesophyll protoplasts was determined. Substantial activity of UDPG pyrophosphorylase was found in both mesophyll and bundle sheath cells while glycerate kinase was localized only in mesophyll cells. From C(4) mesophyll protoplasts, UDPG pyrophosphorylase was found to be cytoplasmic while glycerate kinase appears exclusively localized in the chloroplasts as determined by differential centrifugation and sucrose density gradients.It seems that in both C(3) and C(4) plants, the terminal steps of sucrose synthesis occur exclusively in the cytoplasm while carbon flow in the glycolate pathway to sucrose must occur through glycerate kinase in the chloroplasts. The localization of glycerate kinase in mesophyll cells of C(4) plants may have further implications for intercellular flow of carbon during metabolism in the glycolate pathway in these species.
...
PMID:Localization of glycerate kinase and some enzymes for sucrose synthesis in c(3) and c(4) plants. 1666 Dec 77

Specific activities of NADP-malic enzyme, NAD-malic enzyme, phosphoenolpyruvate carboxykinase and pyruvate, orthophosphate dikinase in various cells of Vicia faba L. leaflets were determined. Expressed on dry weight, chlorophyll or protein basis, the averages for NADP- and NAD-malic enzyme specific activities were higher in guard cells than in photosynthetic parenchyma cells. Malic enzyme-specific activities were also high in epidermal cells. Phosphoenolypyruvate carboxykinase activity was not detected in Vicia leaf extracts or guard cells; the assay techniques were validated by mixed Vicia-Brachiaria leaf extraction and assays on nanogram samples of Brachiaria bundlesheath cells. It was inferred from these data that guard cell malate depletion is by decarboxylation to pyruvate in the epidermal layer, but how the various epidermal cells interact remains obscure.Pyruvate, orthophosphate dikinase activity could not be demonstrated unequivocally in Vicia leaf extracts, Vicia guard cell protoplast extracts, or in Vicia guard cells. The assay techniques were validated by mixed Vicia-Kochia leaf extraction and assays on nanogram samples of Kochia mesophyll cells. How (or if) pyruvate is phosphorylated by epidermal tissue for entry into gluconeogenesis is unknown.
...
PMID:High Levels of Malic Enzyme Activities in Vicia faba L. Epidermal Tissue. 1666 49

Mesembryanthemum crystallinum, a halophilic, inducible Crassulacean acid metabolism (CAM) species, was grown at NaCl concentrations of 20 and 400 millimolar in the rooting medium. Plants from the low salinity treatment showed exclusively C(3)-photosynthetic net CO(2) fixation, whereas plants exposed to the high salinity level exhibited net CO(2) dark fixation involving CAM. Mesophyll protoplasts, isolated from both tissues, were gently ruptured, and the intracellular localization of enzymes was studied following differential centrifugation and Percoll density gradient centrifugation of protoplast extracts. Both centrifugation techniques resulted in the separation of intact chloroplasts, with up to 90% yield, from other organelles and the nonparticulate fraction of cells. Enzymes were identified by determination of activity and by sodium dodecyl sulfate gel electrophoresis of enzyme protein.Experiments established the extraorganellar (cytoplasmic) location of phosphoenolpyruvate carboxylase, enolase, phosphoglyceromutase, and NADP-malic enzyme; the mitochondrial location of NAD-malic enzyme; and the chloroplastic location of pyruvate, Pi dikinase. NAD-glyceraldehyde-3-phosphate dehydrogenase, phosphohexose isomerase, and phosphoglycerate kinase were associated with both cytoplasm and chloroplasts. NADP-dependent malate dehydrogenase activity was found in both the chloroplastic and extrachloroplastic fractions; the activity in the chloroplast showed an optimum at pH 8.0 and was dependent upon preincubation of enzyme with dithiothreitol. The extrachloroplastic activity showed an optimum at pH 6.5 and was independent of pretreatment with dithiothreitol. Protoplast extracts of M. crystallinum performing CAM exhibited higher activities (expressed per mg chlorophyll per min) of phosphoenolpyruvate carboxylase, pyruvate, Pi dikinase, NADP-malic enzyme, NAD-malic enzyme, NADP-malate dehydrogenase, enolase, phosphoglyceromutase, NAD-glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, and phosphohexose isomerase than protoplast extracts from M. crystallinum not exhibiting CAM. The increase in total activity of the latter three enzymes following exposure of plants to 400 millimolar NaCl and the development of CAM was due to specific increases in the levels of activity in the cytoplasm.
...
PMID:Intracellular Localization of Enzymes of Carbon Metabolism in Mesembryanthemum crystallinum Exhibiting C(3) Photosynthetic Characteristics or Performing Crassulacean Acid Metabolism. 1666 97

A mechanical isolation procedure was developed to study the respiratory properties of mitochondria from the mesophyll and bundle sheath tissue of Panicum miliaceum, a NAD-malic enzyme C(4) plant. A mesophyll fraction and a bundle sheath fraction were obtained from young leaves by differential mechanical treatment. The purity of both fractions was about 80%, based on analysis of the cross-contamination of ribulose bisphosphate carboxylase activity and phosphoenolpyruvate carboxylase activity.Mitochondria were isolated from the two fractions by differential centrifugation and Percoll density gradient centrifugation. The enrichment of mitochondria relative to chloroplast material was about 75-fold in both preparations.Both types of mitochondria oxidized NADH and succinate with respiratory control. Malate oxidation in mesophyll mitochondria was sensitive to KCN and showed good respiratory control. In bundle sheath mitochondria, malate oxidation was largely insensitive to KCN and showed no respiratory control. The oxidation was strongly inhibited by salicylhydroxamic acid, showing that the alternative oxidase was involved. The bundle sheath mitochondria of this type of C(4) species contribute to C(4) photosynthesis through decarboxylation of malate. Malate oxidation linked to an uncoupled, alternative pathway may allow decarboxylation to proceed without the restraints which might occur via coupled electron flow through the cytochrome chain.
...
PMID:Isolation of Mitochondria from Leaf Tissue of Panicum miliaceum, a NAD-Malic Enzyme Type C(4) Plant. 1666 92

The quantum yield for CO(2) uptake was measured on a number of C(3) and C(4) monocot and dicot species. Under normal atmospheric conditions (330 microliters per liter CO(2), 21% O(2)) and a leaf temperature of 30 degrees C, the average quantum yields (moles CO(2) per einstein) were as follows: 0.052 for C(3) dicots, 0.053 for C(3) grasses, 0.053 for NAD-malic enzyme type C(4) dicots, 0.060 for NAD-malic enzyme type C(4) grasses, 0.064 for phosphoenolpyruvate carboxykinase type C(4) grasses, 0.061 for NADP-malic enzyme C(4) dicots, and 0.065 for NADP-malic enzyme type C(4) grasses. The quantum yield under normal atmospheric conditions was temperature dependent in C(3) species, but apparently not in C(4) species. Light and temperature conditions during growth appeared not to influence quantum yield. The significance of variation in the quantum yields of C(4) plants was discussed in terms of CO(2) leakage from the bundle sheath cells and suberization of apoplastic regions of the bundle sheath cells.
...
PMID:Variation in Quantum Yield for CO(2) Uptake among C(3) and C(4) Plants. 1666 57

Experiments were conducted with several Panicum species (representing the different C(4) subtypes) to examine the light modulation of sucrose phosphate synthase (SPS) activity and the effect of illumination on the distribution of SPS activity between mesophyll cells (MC) and bundle sheath cells (BSC). Activity of SPS in the light decreased in the order: C(4) > C(3)-C(4) intermediate > C(3). In illuminated leaves, SPS activities were similar among the three C(4) subtypes, but SPS activity was higher for NAD-malic enzyme (NAD-ME) species with centripetal chloroplasts in BSC (NAD-ME(P) species) than for NAD-ME species with centrifugal chloroplasts in BSC (NAD-ME(F) species). Transfer of plants into darkness for 30 minutes resulted in decreased SPS activity for all species tested except Panicum bisulcatum (C(3) species) and Panicum virgatum (NAD-ME(P) species) which showed little or no change. All C(4) subtypes had some SPS activity both in MC and BSC. In the light, SPS activity was mainly in the MC for NADP-ME, NAD-ME(F) and phosphoenolpyruvate carboxykinase species, while it was mainly in the BSC for NAD-ME(P) species. In the dark, for all C(4) subtypes, SPS activity in the MC was decreased to a greater extent than that in the BSC. It is intriguing that NAD-ME(F) and NAD-ME(P) species differed in the activity and distribution of SPS activity between MC and BSC, although they are otherwise identical in the photosynthetic carbon assimilation pathway. Diurnal changes in SPS activity in the MC and BSC were also examined in maize leaves. SPS activity in the MC in maize leaves was high and relatively constant throughout the middle of the light period, dropped rapidly after sunset and increased again prior to the light period. On the other hand, SPS activity in the BSC was lower and changed more coincidently with light intensity than that in the MC. The results suggested that light activation of SPS activity located in the BSC may require higher irradiance for saturation than the SPS in the MC. We conclude that SPS may function in both MC and BSC for sucrose synthesis in the light, particularly at high light intensity, while in the dark, the major function may be in the BSC during starch degradation.
...
PMID:Light Modulation and Localization of Sucrose Phosphate Synthase Activity between Mesophyll Cells and Bundle Sheath Cells in C(4) Species. 1666 68

Photosynthetic rates, chlorophyll content, and activities of several photosynthetic enzymes were determined per cell, per unit DNA, and per unit leaf area in five ploidal levels of the C(4) dicot Atriplex confertifolia. Volumes of bundle sheath and mesophyll protoplasts were measured in enzymatic digestions of leaf tissue. Photosynthetic rates per cell, contents of DNA per cell, and activities of the bundle sheath enzymes ribulose 1,5-bisphosphate carboxylase (RuBPC) and NAD-malic enzyme per cell were correlated with ploidal level at 99% or 95% confidence levels, and the results suggested a near proportional relationship between gene dosage and gene products. There was also a high correlation between volume of mesophyll and bundle sheath cells and the ploidal level. Contents of DNA per cell, activity of RuBPC per cell, and volumes of cells were correlated with photosynthetic rate per cell at the 95% confidence level. The mesophyll cells did not respond to changes in ploidy like the bundle sheath cells. In the mesophyll cells the chlorophyll content per cell was constant at different ploidal levels, there was less increase in cell volume than in bundle sheath cells with an increase in ploidy, and there was not a significant correlation (at 95% level) of phosphoenolpyruvate carboxylase activity or content and pyruvate,Pi dikinase activity with increase in ploidy. The number of photosynthetic cells per unit leaf area progressively decreased with increasing ploidy from diploid to hexaploid, but thereafter remained constant in octaploid and decaploid plants. Numbers of cells per leaf area were not correlated with cell volumes. The mean photosynthetic rates per unit leaf area were lowest in the diploid, similar in 4x, 6x, and 8x, and highest in the decaploid. The photosynthetic rate per leaf area was highly correlated with the DNA content per leaf area.
...
PMID:Effects of Polyploidy on Photosynthetic Rates, Photosynthetic Enzymes, Contents of DNA, Chlorophyll, and Sizes and Numbers of Photosynthetic Cells in the C(4) Dicot Atriplex confertifolia. 1666 25

An artificial Na(+) gradient across the envelope (Na(+) jump) enhanced pyruvate uptake in the dark into mesophyll chloroplasts of a C(4) plant, Panicum miliaceum (NAD-malic enzyme type) (J Ohnishi, R Kanai [1987] FEBS Lett 219:347). In the present study, (22)Na(+) and pyruvate uptake were examined in mesophyll chloroplasts of several species of C(4) plants. Enhancement of pyruvate uptake by a Na(+) jump in the dark was also seen in mesophyll chloroplasts of Urochloa panicoides and Panicum maximum (phosphoenolpyruvate carboxykinase types) but not in Zea mays or Sorghum bicolor (NADP-malic enzyme types). In mesophyll chloroplasts of P. miliaceum and P. maximum, pyruvate in turn enhanced Na(+) uptake in the dark when added together with Na(+). When flux of endogenous Na(+) was measured in these mesophyll chloroplasts preincubated with (22)Na(+), pyruvate addition induced Na(+) influx, and the extent of the pyruvate-induced Na(+) influx positively correlated with that of pyruvate uptake. A Na(+)/H(+) exchange ionophore, monensin, nullified all the above mutual effects of Na(+) and pyruvate in mesophyll chloroplasts of P. miliaceum, while it accelerated Na(+) uptake and increased equilibrium level of chloroplast (22)Na(+). Measurements of initial uptake rates of pyruvate and Na(+) gave a stoichiometry close to 1:1. These results point to Na(+)/pyruvate cotransport into mesophyll chloroplasts of some C(4) plants.
...
PMID:Involvement of na in active uptake of pyruvate in mesophyll chloroplasts of some c(4) plants : na/pyruvate cotransport. 1666 76

Properties of C4 photosynthesis were examined in Amaranthus cruentus L. (NAD-malic enzyme (ME) subtype, dicot) grown under different light and nitrogen (N) conditions, from the viewpoint of N investment into their photosynthetic components. In low-light (LL) leaves, chlorophyll content per leaf area was greater and chlorophyll alb ratio was lower than in high-light (HL) leaves. These indicate that LL leaves invest more N into their light-harvesting systems. However, this N investment did not contribute to the increase in the quantum yield of photosynthesis on the incident photon flux density (PFD) basis (Qi) in LL leaves. N allocation to ribulose 1,5-bisphosphate carboxylasel oxygenase (Rubisco) was significantly higher in HL-high N (HN) leaves than in other leaves. On the other hand, N allocation to C4 enzymes [phosphoenolpyruvate carboxylase (PEPC) and pyruvate Pi dikinase (PPDK)] was unaffected by the growth conditions. Maximum photosynthetic rates (Pmax) per Rubisco content were similar irrespective of the growth light treatments. Carbon isotope ratios (delta13 C) in the leaf dry matter were more negative in LL leaves than in HL leaves (LL = -19.3% per hundred, HL = -16.0% per hundred) and independent of leaf N. Vein density was highest in HL-HN leaves, and leaf thickness was unaffected by the growth light treatments. From these results, we conclude that A. cruentus leaves would not acclimate efficiently to low growth light.
...
PMID:Effects of growth light and nitrogen nutrition on the organization of the photosynthetic apparatus in leaves of a C4 plant, Amaranthus cruentus. 1708 Jun 18


<< Previous 1 2 3 4 5 Next >>

---