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

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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)

Photosynthetically active bundle sheath strands capable of assimilating up to 8 micromoles CO(2) per milligram chlorophyll per hour have been isolated from fully expanded leaves of Zea mays L. Mesophyll cell contamination of the preparations was negligible, as evidenced by light and electron microscopy and by a high ratio of chlorophyll a to chlorophyll b in the strands. Ribose 5-phosphate markedly stimulated the rate of photosynthetic (14)CO(2) fixation by the isolated strands. In contrast, both pyruvate and phosphoenolpyruvate had a comparatively small stimulatory effect on bundle sheath (14)CO(2) fixation. After 5 minutes of photosynthesis in (14)C-bicarbonate, 95% of the incorporated (14)C was found in compounds other than C(4)-dicarboxylic acids, most notably in 3-phosphoglycerate and sugar phosphates. A similar distribution of (14)C was observed in the presence of exogenous ribose 5-phosphate. Extracts of bundle sheath strands contained high specific activities of "malic" enzyme, phosphoglycolate phosphatase, hydroxypyruvate reductase, and ribulose 1,5-diphosphate carboxylase, whereas the specific activities of NADP(+)-malate dehydrogenase and phosphopyruvate carboxylase were extremely low. These results indicate that the Calvin cycle occurs in the bundle sheath cells of maize.
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PMID:Photosynthetic carbon metabolism in isolated maize bundle sheath strands. 1665 10

Mesophyll protoplasts and bundle sheath strands of maize (Zea mays L.) leaves have been isolated by enzymatic digestion with cellulase. Mesophyll protoplasts, enzymatically released from maize leaf segments, were further purified by use of a polyethylene glycol-dextran liquid-liquid two phase system. Bundle sheath strands released from the leaf segments were isolated using filtration techniques. Light and electron microscopy show separation of the mesophyll cell protoplasts from bundle sheath strands. Two varieties of maize isolated mesophyll protoplasts had chlorophyll a/b ratios of 3.1 and 3.3, whereas isolated bundle sheath strands had chlorophyll a/b ratios of 6.2 and 6.6. Based on the chlorophyll a/b ratios in mesophyll protoplasts, bundle sheath cells, and whole leaf extracts, approximately 60% of the chlorophyll in the maize leaves would be in mesophyll cells and 40% in bundle sheath cells. The purity of the preparations was also evident from the exclusive localization of phosphopyruvate carboxylase (EC 4.1.1.31) and NADP-dependent malate dehydrogenase (EC 1.1.1) in mesophyll cells and ribulose 1,5-diphosphate carboxylase (EC 4.1.1.39), phosphoribulokinase (EC 2.7.1.19), and "malic enzyme" (EC 1.1.1.40) in bundle sheath cells. NADP-glyceraldehyde 3-phosphate dehydrogenase (EC 1.2.1.13) was found in both mesophyll and bundle sheath cells, while ribose 5-phosphate isomerase (EC 5.3.1.6) was primarily found in bundle sheath cells. In comparison to the enzyme activities in the whole leaf extract, there was about 90% recovery of the mesophyll enzymes and 65% recovery of the bundle sheath enzymes in the cellular preparations.
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PMID:Separation of mesophyll protoplasts and bundle sheath cells from maize leaves for photosynthetic studies. 1665 79

A number of plant species were surveyed to obtain pure leaf epidermal tissue in quantity. Commelina communis L. and Tulipa gesnariana L. (tulip) were chosen for further work. Chlorophyll a/b ratios of epidermal tissues were 2.41 and 2.45 for C. communis and tulip, respectively. Phosphoenolpyruvate carboxylase, ribulose-1,5-diphosphate carboxylase, malic enzyme, and NAD(+) and NADP(+) malate dehydrogenases were assayed with epidermal tissue and leaf tissue minus epidermal tissue. In both species, there was less ribulose 1,5-diphosphate than phosphoenolpyruvate carboxylase activity in epidermal tissue whether expressed on a protein or chlorophyll basis whereas the reverse was true for leaf tissue minus epidermal tissue. In both species, malic enzyme activities were higher in epidermal tissue than in the remaining leaf tissue when expressed on a protein or chlorophyll basis. In both species, NAD(+) and NADP(+) malate dehydrogenase activities were higher in the epidermal tissue when expressed on a chlorophyll basis; however, on a protein basis, the converse was true. Microautoradiography of C. communis epidermis and histochemical tests for keto acids suggested that CO(2) fixation occurred predominantly in the guard cells. The significance and possible location of the enzymes are discussed in relation to guard cell metabolism.
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PMID:Carbon dioxide metabolism in leaf epidermal tissue. 1665 81

The mutation of a nuclear gene in peanut (Arachis hypogaea L.) plants results in a reduced light-dependent development of chloroplast fine structure, soluble protein, ribulose-1, 5-diP carboxylase, NADP-glyceraldehyde-3-P dehydrogenase, fructose-1, 6-diP aldolase, glycerate-3-P kinase, phosphoenolpyruvate carboxylase, malate dehydrogenase, and dark respiration during the 72-hour lag period of chlorophyll synthesis in dark-grown leaves exposed to continuous light. The mutation has pleiotropic affects. Kinetic analysis shows there is also a 72-hour lag period in the light-dependent development of NADP-glyceraldehyde-3-P dehydrogenase and fructose-1, 6-diP aldolase in the mutant leaves, whereas there is no lag in the development of NAD-malate dehydrogenase and dark respiration. There is minimal development of the chloroplast during the 72-hour mutationally induced lag period, but there is pronounced cytoplasmic and mitochondrial activity during this phase. There is a 24-hour lag period in the light-dependent enlargement of the mutant leaves. At the completion of leaf enlargement, chloroplast differentiation is initiated. The mutation does not result in any chloroplast deletions, it only affects the timing of the synthesis of these components.Elimination of the lag period in leaf enlargement and chloroplast development (potentiation) requires a preliminary 72- to 96-hour dark period before exposing the dark-grown leaves to continuous light. There is extensive development of the etioplasts during this dark period. These results establish that the nuclear gene mutation affects the early stages of plastid development and not the light-dependent synthesis of plastid components. The nuclear gene may code for the regulation of the synthesis of a component (nutrient) in the dark (or during the lag phase in the light) which is essential for the development of mesophyll cells and plastids. Although, the chloroplast is a semi-autonomous organelle, nuclear gene control of chloroplast differentiation may not be independent of cellular growth.
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PMID:Elimination of the lag period in chloroplast development in a chlorophyll mutant of peanuts. 1665 82

Chloroplasts isolated from powdery mildew-infected (Erysiphe polygoni DC) sugar beet leaves (Beta vulgaris L) showed a reduction in the rate of electron transport and in the accompanying ATP formation in noncyclic photophosphorylation (water as electron donor, NADP as electron acceptor) and little or no change in the rate of ATP formation in cyclic photophosphorylation catalyzed by phenazine methosulfate. The inhibition of noncyclic photophosphorylation appeared to lead in the parent leaves to a decreased rate of photosynthetic CO(2) assimilation and a shift in products resulting in a relative increase of amino acids. These changes were accompanied by alterations in chloroplast ultrastructure and by a reduction in the activity of enzymes necessary for the formation of organic acids (phosphoenolpyruvate carboxylase and malate dehydrogenase). These results are similar to the findings of Montalbini and Buchanan (1974 Physiol. Plant Pathol. 4: 191-196) with chloroplasts from rust-infected Vicia faba leaves.
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PMID:Effect of powdery mildew infection on photosynthesis by leaves and chloroplasts of sugar beets. 1665 11

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

Arundinella hirta L. is a C(4) plant having an unusual C(4) leaf anatomy. Besides mesophyll and bundle sheath cells, A. hirta leaves have specialized parenchyma cells which look morphologically like bundle sheath cells but which lack vascular connections and are located between veins, running parallel to them. Activities of phosphoenolpyruvate and ribulose-1,5-bisphosphate carboxylases and phosphoenolpyruvate carboxykinase, NADP-and NAD-malic enzymes were determined for whole leaf extracts and isolated mesophyll protoplasts, specialized parenchyma cells, and bundle sheath cells. The data indicate that A. hirta is a NADP-malic enzyme type C(4) species. In addition, specialized parenchyma cells and bundle sheath cells are enzymatically alike. Compartmentation of enzymes followed the C(4) pattern with phosphoenolpyruvate carboxylase being restricted to mesophyll cells while ribulose-1,5-bisphosphate carboxylase and decarboxylating enzymes were restricted to bundle sheath and specialized parenchyma cells.
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PMID:Distribution of Photosynthetic Enzymes between Mesophyll, Specialized Parenchyma and Bundle Sheath Cells of Arundinella hirta. 1666 Jun 81

The intracellular locations of six key enzymes of Crassulacean acid metabolism were determined using enzymically isolated mesophyll protoplasts of Sedum praealtum D.C. Data from isopycnic sucrose density gradient centrifugation established the chloroplastic location of pyruvate Pi dikinase, the mitochondrial location of NAD-linked malic enzyme, and exclusively nonparticulate (not associated with chloroplasts, peroxisomes, or mitochondria) locations of phosphoenolpyruvate carboxylase, NADP-linked malic enzyme, enolase, and phosphoglycerate mutase. The consequences of this enzyme distribution with respect to compartmentalization of the pathway and the transport of metabolites in Crassulacean acid metabolism are discussed.
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PMID:Intracellular Localization of Some Key Enzymes of Crassulacean Acid Metabolism in Sedum praealtum. 1666 Aug 3

The CO(2) compensation point of the submersed aquatic macrophyte Hydrilla verticillata varied from high (above 50 microliters per liter) to low (10 to 25 microliters per liter) values, depending on the growth conditions. Plants from the lake in winter or after incubation in an 11 C/9-hour photoperiod had high values, whereas summer plants or those incubated in a 27 C/14-hour photoperiod had low values. The plants with low CO(2) compensation points exhibited dark (14)CO(2) fixation rates that were up to 30% of the light fixation rates. This fixation reduced respiratory CO(2) loss, but did not result in a net uptake of CO(2) at night. The low compensation point plants also showed diurnal fluctuations in titratable acid, such as occur in Crassulacean acid metabolism plants. However, dark fixation and diurnal acid fluctuations were negligible in Hydrilla plants with high CO(2) compensation points.Exposure of the low compensation point plants to 20 micromolar (14)CO(2) resulted in 60% of the (14)C being incorporated into malate and aspartate, with only 16% in sugar phosphates. At a high CO(2) level, the C(4) acid label was decreased. A pulse-chase study indicated that the (14)C in malate, but not aspartate, decreased after a long (270-second) chase period; thus, the C(4) acid turnover was much slower than in C(4) plants.Phosphoenolpyruvate carboxylase activity was high (330 micromoles per milligram chlorophyll per hour), as compared to ribulose bisphosphate carboxylase (20 to 25), in the plants with low compensation points. These plants also had a pyruvate, Pi dikinase activity in the leaves of 41 micromoles per milligram chlorophyll per hour, which suggests they are not C(3) plants. NAD- and NADP(+)-malate dehydrogenase activities were 6136 and 24.5 micromoles per milligram chlorophyll per hour, respectively. Of the three decarboxylating enzymes assayed, the activities of NAD- and NADP(+)-malic enzyme were 104.2 and 23.7 micromoles per milligram chlorophyll per hour, while phosphoenolpyruvate carboxykinase was only 0.2.Low compensation point Hydrilla plants fix some CO(2) into C(4) acids, which can be decarboxylated for later refixation, presumably into the Calvin cycle. Refixation would be advantageous in summer lake environments where the CO(2) levels are high at night but low during the day. Hydrilla does not fit any of the present photosynthetic categories, and may have to be placed into a new group, together with other submersed aquatic macrophytes that have environmentally variable CO(2) compensation points.
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PMID:C(4) Acid Metabolism and Dark CO(2) Fixation in a Submersed Aquatic Macrophyte (Hydrilla verticillata). 1666 Nov 84

Incubation under water in a 30 C/14-hour or 12 C/10-hour photoperiod caused the CO(2) compensation points of 10 aquatic macrophytes to decrease below 25 or increase above 50 microliters CO(2) per liter, respectively. Submerged and aerial leaves of two amphibious angiosperms (Myriophyllum brasiliense and Proserpinaca palustris) maintained high compensation points when incubated in air but, when the submerged or aerial leaves of Proserpinaca were incubated under water, the compensation points dropped as low as 10. This suggests that, in addition to temperature and photoperiod, some factor associated with submergence regulates the compensation point of aquatic plants. In the high-compensation point plants, photorespiration, as a percentage of net photosynthesis, was equivalent to that in terrestrial C(3) plants. For Hydrilla verticillata, the decreasing CO(2) compensation points (110, 40, and 10) were associated with reduced photorespiration, as indicated by decreased O(2) inhibition, decreased rates of CO(2) evolution into CO(2)-free air, and increased net photosynthetic rates.The decrease in the CO(2) compensation points of Hydrilla, Egeria densa, and Cabomba caroliniana was accompanied by an increase in the activity of phosphoenolpyruvate, but not of ribulose bisphosphate, carboxylase. In Hydrilla, several C(4) enzymes also increased in activity to the following levels (micromoles per gram fresh weight per hour): pyruvate Pi dikinase (35), pyrophosphatase (716), adenylate kinase (525), NAD and NADP malate dehydrogenase (6565 and 30), NAD and NADP malic enzymes (239 and 44), and aspartate and alanine aminotransferases (357 and 85), whereas glycolate oxidase (6) and phosphoglycolate and phosphoglycerate phosphatases (76 and 32) showed no change. Glycolate dehydrogenase and phosphoenolpyruvate carboxykinase were undetectable. The reduced photorespiration in these plants may be due to increased CO(2) fixation via a C(4) acid pathway. However, for three Myriophyllum species, some other mechanism appears operative, as phosphoenolpyruvate carboxylase was not increased in the low compensation point state, and ribulose bisphosphate carboxylase remained the predominant carboxylation enzyme.
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PMID:Induction of reduced photorespiratory activity in submersed and amphibious aquatic macrophytes. 1666 70


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