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)

Ribulose bisphosphate carboxylase/oxygenase (RuBPCase) from several plants had substantially greater activity in extracts from lightexposed leaves than dark leaves, even when the extracts were incubated in vitro with saturating HCO(3) (-) and Mg(2+) concentrations. This occurred in Glycine max, Lycopersicon esculentum, Nicotiana tabacum, Panicum bisulcatum, and P. hylaeicum (C(3)); P. maximum (C(4) phosphoenolpyruvate carboxykinase); P. milioides (C(3)/C(4)); and Bromelia pinguin and Ananas comosus (Crassulacean acid metabolism). Little or no difference between light and dark leaf extracts of RuBPCase was observed in Triticum aestivum (C(3)); P. miliaceum (C(4) NAD malic enzyme); Zea mays and Sorghum bicolor (C(4) NADP malic enzyme); Moricandia arvensis (C(3)/C(4)); and Hydrilla verticillata (submersed aquatic macrophyte). It is concluded that, in many plants, especially Crassulacean acid metabolism and C(3) species, a large fraction of ribulose-1,5-bisphosphate carboxylase/oxygenase in the dark is in an inactivatable state that cannot respond to CO(2) and Mg(2+) activation, but which can be converted to an activatable state upon exposure of the leaf to light.
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PMID:Dark/Light modulation of ribulose bisphosphate carboxylase activity in plants from different photosynthetic categories. 1666 37

Light-induced swelling of guard cell protoplasts (GCP) from Vicia faba was accompanied by increases in content of K(+) and malate. DCMU inhibited the increase of K(+) and malate, and consequently swelling.Effect of light on the activity of selected enzymes that take part in malate formation was studied. When isolated GCP were illuminated, NADP-malate dehydrogenase (NADP-MDH) was activated, and the activity reached a maximum within 5 minutes. The enzyme activity underwent 5- to 6-fold increase in the light. Upon turning off the light, the enzyme was inactivated in 5 minutes NAD-MDH and phosphoenolpyruvate carboxylase (PEPC) were not influenced by light. The rapid light activation of NADP-MDH was inhibited by DCMU, suggesting that the enzyme was activated by reductants from the linear electron transport in chloroplasts. An enzyme localization study by differential centrifugation indicates that NADP-MDH is located in the chloroplasts, NAD-MDH in the cytosol and mitochondria, and PEPC in the cytosol. After light activation, the activity of NADP-MDH in guard cells was 10 times that in mesophyll cells on a chlorophyll basis. The physiological significance of light-dependent activation of NADP-MDH in guard cells is discussed in relation to stomatal movement.
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PMID:Light Activation of NADP-Malate Dehydrogenase in Guard Cell Protoplasts from Vicia faba L. 1666 99

Regenerating maize A188 tissue cultures were examined for the presence of enzymes involved in C(4) photosynthesis, for cell morphology, and for (14)C labeling kinetics to study the implementation of this pathway during plant development. For comparison, sections of maize seedling leaves were examined. Protein blot analysis using antibodies to leaf enzymes showed a different profile of these enzymes during the early stages of shoot regeneration from callus from the closely-coordinated profile observed in seedling leaves. Pyruvate orthophosphate dikinase (PPDK) (EC 2.7.9.1) and phosphoenolpyruvate carboxylase (PEPC) (EC 4.1.1.31) were found in nonchlorophyllous callus while ribulose 1,5-bisphosphate carboxylase (RuBPC, EC 4.1.1.39) and malic enzyme, NADP-specific (ME-NADP) (EC 1.3.1.37) were not detectable until later.Enzyme activity assays showed the presence of ME-NADP as well as PEPC and PPDK in nonchlorophyllous callus. However, the activities of ME-NADP and PEPC had properties similar to those of the enzymes from C(3) leaves and from etiolated C(4) leaf tissues, but differing from the corresponding enzymes in the mature leaf.Immunoprecipitation of in vitro translation products of poly(A)RNA extracted from embryoid-forming callus showed both the 110 kilodalton precursor to chloroplast PPDK and the 94 kilodalton polypeptide. Therefore, the chloroplast tye of PPDK mRNA is present prior to the appearance of leaf morphology.Analysis of the labeled products of (14)CO(2) fixation by nonchlorophyllous calli indicated beta-carboxylation to give acids of the tricarboxylic acid cycle, but no incorporation into phosphoglycerate. With greening of the callus, some incorporation into phosphoglycerate and sugar phosphates occurred, and this increased in shoots as they developed, although with older shoots the increase in beta-carboxylation products was even greater. Analysis of enzyme levels in young leaf sections by protein blot and of (14)C-labeling patterns in the present study are in general agreement with enzyme activity determinations of previous studies, providing additional information about PPDK levels, and supporting the model proposed for developing young leaves.These results suggest that maize leaves begin to express C(4) enzymes during ontogeny through several stages from greening and cell differentiation as seen in the callus and then shoot formation, and finally acquire capacity for full C(4) photosynthesis during leaf development concomitant with the development of Kranz anatomy and accumulation of large amounts of enzymes involved in carbon metabolism.
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PMID:Appearance and accumulation of c(4) carbon pathway enzymes in developing maize leaves and differentiating maize a188 callus. 1666 21

Soluble protein has been extracted from sections of wheat leaves, from base to tip, and the content of several key enzymes of photosynthetic carbon assimilation in each section has been determined by the protein blot method. In the first leaf, ribulose 1,5-bisphosphate carboxylase (RuBPC) (EC 4.1.1.39) in the basal 0 to 1 centimeter section is about 12% the level in the tip section, whereas phosphoenolpyruvate carboxylase (EC 4.1.1.31) is present in small amounts in the basal section and does not change much in the tip. Pyruvate orthophosphate dikinase (PPDK) (EC 2.7.9.1) first appears in the 4 to 6 centimeter section and increases gradually with development to 10-fold in the tip. Malic enzyme, NADP-dependent (EC 1.3.1.37) also appears in the 4 to 6 centimeter section but remains low to the tip.Fixation of (14)CO(2) by wheat leaf base sections resulted in 42% of total incorporation into malate and aspartate, indicating beta-carboxylation, whereas in the tip section these labeled compounds were only 8% of the total. Although the amount of PPDK in wheat leaves is only 1 to 3% of that in maize leaves, this C(3) PPDK may have a limited role in photosynthesis leading to formation of C(4) compounds. The possibility of a further role, similar to that in C(4) plants, but for intracellular carbon transport in wheat leaves is discussed. The presence of malic dehydrogenase, NADP-specific (EC 1.1.1.82) in wheat leaf chloroplasts was shown, a necessary though not sufficient condition for such a proposed role. Assuming each of the four enzymes associated with C(4) carbon transport were fully active in vivo during photosynthesis, PPDK would still be rate limiting, even in the leaf tip where its activity is maximal. Possible evolutionary and breeding implications are discussed.
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PMID:Appearance and accumulation of c(4) carbon pathway enzymes in developing wheat leaves. 1666 22

Two naturally occurring species of the genus Alternanthera, namely A. ficoides and A. tenella, were identified as C(3)-C(4) intermediates based on leaf anatomy, photosynthetic CO(2) compensation point (Gamma), O(2) response of small ghe, Cyrillic, light intensity response of small ghe, Cyrillic, and the activities of key enzymes of photosynthesis. A. ficoides and A. tenella exhibited a less distinct Kranz-like leaf anatomy with substantial accumulation of starch both in mesophyll and bundle sheath cells. Photosynthetic CO(2) compensation points of these two intermediate species at 29 degrees C were much lower than in C(3) plants and ranged from 18 to 22 microliters per liter. Although A. ficoides and A. tenella exhibited similar intermediacy in small ghe, Cyrillic, the apparent photorespiratory component of O(2) inhibition in A. ficoides is lower than in A. tenella. The small ghe, Cyrillic progressively decreases from 35 microliters per liter at lowest light intensity to 18 microliters per liter at highest light intensity in A. tenella. It was, however, constant in A. ficoides at 20 to 25 microliters per liter between light intensities measured. The rates of net photosynthesis at 21% O(2) and 29 degrees C by A. ficoides and A. tenella were 25 to 28 milligrams CO(2) per square decimeter per hour which are intermediate between values obtained for Tridax procumbens and A. pungens, C(3) and C(4) species, respectively. The activities of key enzymes of C(4) photosynthesis, phosphoenolpyruvate carboxylase, pyruvate Pi dikinase, NAD malic enzyme, NADP malic enzyme and phosphoenolpyruvate carboxykinase in the two intermediates, A. ficoides and A. tenella are very low or insignificant. Results indicated that the relatively low apparent photorespiratory component in these two species is presumably the basis for the C(3)-C(4) intermediate photosynthesis.
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PMID:C(3)-C(4) Intermediate Species in Alternanthera (Amaranthaceae) : Leaf Anatomy, CO(2) Compensation Point, Net CO(2) Exchange and Activities of Photosynthetic Enzymes. 1666 34

Photosynthetic properties were examined in several hcf (high chlorophyll fluorescence 11, 21, 42 and 45) nuclear recessive mutants of maize which were previously found to have normal photochemistry and low CO(2) fixation. Mutants usually either died after depletion of seed reserves (about 18 days after planting), or survived with slow growth up to 7 or 8 weeks. Both the activity and quantity of ribulose 1,5-bisphosphate carboxylase (Rubisco) were low in the mutants (5-25% of the normal siblings on a leaf area basis) and the loss of Rubisco tended to parallel the reduction in photosynthetic capacity. The Rubisco content in the mutants was often marginal for photosynthetic carbon gain, with some leaves and positions along a leaf having no net photosynthesis, while other leaves had a low carbon gain. Conversely, the activities of C(4) cycle enzymes, phosphoenolpyruvate carboxylase, pyruvate, Pi dikinase, NADP-malate dehydrogenase, and NADP-malic enzyme, were the same or only slightly reduced compared to the normal siblings. The mutants had about half as much chlorophyll content per leaf area as the normal green plants. However, the Rubisco activity in the mutants was low on both a leaf area and chlorophyll basis. Low Rubisco activity and lower chlorophyll content may both contribute to the low rates of photosynthesis in the mutants on a leaf area basis.
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PMID:CO(2) Assimilation and Activities of Photosynthetic Enzymes in High Chlorophyll Fluorescence Mutants of Maize Having Low Levels of Ribulose 1,5-Bisphosphate Carboxylase. 1666 42

The activities of key C(4) enzymes in gel-filtered, whole-leaf extracts and the photosynthetic characteristics for reciprocal F(1) hybrids of Flaveria pringlei (C(3)) and F. brownii (C(4)-like species) were measured to determine whether any inherited C(4)-photosynthetic traits are responsible for their reduced CO(2) compensation concentration values (AS Holaday, S Talkmitt, ME Doohan Plant Sci 41: 31-39). The activities of phosphoenolpyruvate carboxylase, pyruvate, orthophosphate dikinase, and NADP-malic enzyme (ME) for the reciprocal hybrids are only about 7 to 17% of those for F. brownii, but are three- to fivefold greater than the activities for F. pringlei. The low activities of these enzymes in the hybrids appear to be the result of a partial dominance of F. pringlei genes over certain F. brownii genes. However, no such dominance occurs with respect to the expression of genes for NADP-malate dehydrogenase, which is as active in the hybrids as in F. brownii. In contrast to the situation with the enzymes above, cytoplasmic factors appear to determine the inheritance of NAD-ME. The NAD-ME activity in each hybrid is comparable to that in the respective maternal parent. Pulse-chase (14)CO(2) incorporation analyses at ambient CO(2) levels indicate that the hybrids initially assimilate 7 to 9% of the total assimilated CO(2) into C(4) acids as compared to 3.5% for F. pringlei. In the hybrids, the percentage of (14)C in malate decreases from an average of 6.5 to 2.1% after a 60-second chase in (12)CO(2)/air. However, this apparent C(4)-cycle activity is too limited or inefficient to substantially alter CO(2) exchange from that in F. pringlei, since the values of net photosynthesis and O(2) inhibition of photosynthesis are similar for the hybrids and F. pringlei. Also, the ratio of the internal to the external CO(2) concentration and the initial slopes of the plot of CO(2) concentration versus net photosynthesis are essentially the same for the hybrids and F. pringlei. At 45 micromoles CO(2) per mole and 0.21 mole O(2) per mole, the hybrids assimilate nearly fivefold more CO(2) into C(4) acids than does F. pringlei. Some turnover of the malate pool occurs in the hybrids, but the labelling of the photorespiratory metabolites, glycine and serine, is the same in these plants as it is in F. pringlei. Thus, although limited C(4)-acid metabolism may operate in the hybrids, we conclude that it is not effective in altering O(2) inhibition of CO(2) assimilation. The ability of the hybrids to assimilate more CO(2) via phosphoenolpyruvate carboxylase at low levels of CO(2) than does F. pringlei may result in an increased rate of reassimilation of photorespiratory CO(2) and CO(2) compensation concentrations below that of their C(3) parent. If the hybrids do possess a limited C(4) cycle, it must operate intracellularly. They are not likely to have inherited an intercellular compartmentation of C(4) enzymes, since F. brownii has incomplete compartmentation of key C(3) and C(4) enzymes.
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PMID:Enzymic and Photosynthetic Characteristics of Reciprocal F(1) Hybrids of Flaveria pringlei (C(3)) and Flaveria brownii (C(4)-Like Species). 1666 69

When Brassica nigra leaf petiole suspension cells were subjected to 7 days of inorganic phosphate (Pi) starvation the extractable activity of: (a) pyrophosphate:fructose 6-phosphate 1-phosphotransferase, nonphosphorylating NADP-glyceraldehyde 3-phosphate dehydrogenase, phosphoenolpyruvate phosphatase, and phosphoenolpyruvate carboxylase increased at least fivefold, (b) phosphorylating NAD-glyceraldehyde 3-phosphate dehydrogenase decreased about sixfold, and (c) ATP:fructose 6-phosphate 1-phosphotransferase, 3-phosphoglycerate kinase, pyruvate kinase, or NAD malic enzyme was not altered. Pi deprivation also resulted in significant reductions in extractable levels of Pi, ATP, ADP, fructose 2,6-bisphosphate, and soluble protein, but caused a sixfold elevation in free amino acid concentrations. No change in inorganic pyrophosphate concentration was observed following Pi starvation. It is hypothesized that pyrophosphate:fructose 6-phosphate 1-phosphotransferase, nonphosphorylating NADP-glyceraldehyde 3-phosphate dehydrogenase, and phosphoenolpyruvate phosphatase bypass nucleotide phosphate or Pi-dependent glycolytic reactions during sustained periods of Pi depletion.
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PMID:Phosphate Starvation Inducible ;Bypasses' of Adenylate and Phosphate Dependent Glycolytic Enzymes in Brassica nigra Suspension Cells. 1666 22

The effects of phosphorus nutrition on several physiological and biochemical parameters of the green alga, Selenastrum minutum, have been examined. Algal cells were cultured in chemostats under conditions of either Pi limitation or nutrient sufficiency. Pi limitation resulted in: (a) a 5-fold lower rate of respiration, (b) a 3-fold decline in rates of photosynthetic carbon dioxide fixation and oxygen evolution, (c) a 3-fold higher rate of dark carbon dioxide fixation, (d) significant increases in activities of phosphoenolpyruvate (PEP) carboxylase and PEP phosphatase (128% and 158% of nutrient sufficient activities, respectively), (e) significant reductions in activities of nonphosphorylating NADP-glyceraldehyde-3-phosphate dehydrogenase and NAD malic enzyme, and (f) no change in levels of ATP:fructose-6-phosphate 1-phosphotransferase, phosphorylating NAD-glyceraldehyde-3-phosphate dehydrogenase, 3-phosphoglycerate kinase, and pyruvate kinase. The intracellular concentrations of Pi, ATP, AMP, soluble protein, and chlorophyll were also significantly reduced in response to Pi limitation. As well, the level of ADP was about 11-fold lower in the Pi-limited cells as compared to the nutrient sufficient controls. It was predicted that because of this low level of ADP, pyruvate kinase catalyzed conversion of PEP to pyruvate may be restricted in Pi-limited cells. During Pi limitation, PEP carboxylase and PEP phosphatase may function to "bypass" the ADP dependent pyruvate kinase, as well as to recycle Pi for its reassimilation into cellular metabolism.
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PMID:Effects of Phosphorus Limitation on Respiratory Metabolism in the Green Alga Selenastrum minutum. 1666 95

Short-term changes in pyridine nucleotides and other key metabolites were measured during the onset of NO(3) (-) or NH(4) (+) assimilation in the dark by the N-limited green alga Selenastrum minutum. When NH(4) (+) was added to N-limited cells, the NADH/NAD ratio rose immediately and the NADPH/NADP ratio followed more slowly. An immediate decrease in glutamate and 2-oxoglutarate indicates an increased flux through the glutamine synthase/glutamate oxoglutarate aminotransferase. Pyruvate kinase and phosphoenolpyruvate carboxylase are rapidly activated to supply carbon skeletons to the tricarboxylic acid cycle for amino acid synthesis. In contrast, NO(3) (-) addition caused an immediate decrease in the NADPH/NADP ratio that was accompanied by an increase in 6-phosphogluconate and decrease in the glucose-6-phosphate/6-phosphogluconate ratio. These changes show increased glucose-6-phosphate dehydrogenase activity, indicating that the oxidative pentose phosphate pathway supplies some reductant for NO(3) (-) assimilation in the dark. A lag of 30 to 60 seconds in the increase of the NADH/NAD ratio during NO(3) (-) assimilation correlates with a slow activation of pyruvate kinase and phosphoenolpyruvate carboxylase. Together, these results indicate that during NH(4) (+) assimilation, the demand for ATP and carbon skeletons to synthesize amino acid signals activation of respiratory carbon flow. In contrast, during NO(3) (-) assimilation, the initial demand on carbon respiration is for reductant and there is a lag before tricarboxylic acid cycle carbon flow is activated in response to the carbon demands of amino acid synthesis.
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PMID:Activation of Respiration to Support Dark NO(3) and NH(4) Assimilation in the Green Alga Selenastrum minutum. 1666 13


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