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

Four species of the genus Flaveria, namely F. anomala, F. linearis, F. pubescens, and F. ramosissima, were identified as intermediate C(3)-C(4) plants based on leaf anatomy, photosynthetic CO(2) compensation point, O(2) inhibition of photosynthesis, and activities of C(4) enzymes. F. anomala and F. ramosissima exhibit a distinct Kranz-like leaf anatomy, similar to that of the C(4) species F. trinervia, while the other C(3)-C(4) intermediate Flaveria species possess a less differentiated Kranz-like leaf anatomy. Photosynthetic CO(2) compensation points of these intermediates at 30 degrees C were very low relative to those of C(3) plants, ranging from 7 to 14 microliters per liter. In contrast to C(3) plants, net photosynthesis by the intermediates was not sensitive to O(2) concentrations below 5% and decreased relatively slowly with increasing O(2) concentration. Under similar conditions, the percentage inhibition of photosynthesis by 21% O(2) varied from 20% to 25% in the intermediates compared with 28% in Lycopersicon esculentum, a typical C(3) species. The inhibition of carboxylation efficiency by 21% O(2) varied from 17% for F. ramosissima to 46% for F. anomala and were intermediate between the C(4) (2% for F. trinervia) and C(3) (53% for L. esculentum) values. The intermediate Flaveria species, especially F. ramosissima, have substantial activities of the C(4) enzymes, phosphoenolpyruvate carboxylase, pyruvate, orthophosphate dikinase, NADP-malic enzyme, and NADP-malate dehydrogenase, indicating potential for C(4) photosynthesis. It appears that these Flaveria species may be true biochemical C(3)-C(4) intermediates.
 ...
PMID:Photosynthetic Characteristics of C(3)-C(4) Intermediate Flaveria Species : I. Leaf Anatomy, Photosynthetic Responses to O(2) and CO(2), and Activities of Key Enzymes in the C(3) and C(4) Pathways. 1666 33

Xerosicyos danguyi Humbert (Cucurbitaceae) is a leaf succulent endemic to Madagascar. Under well-watered conditions, the plant exhibited Crassulacean acid metabolism (CAM) but shifted to a dampened form of CAM, CAM-idling, when subjected to water stress. The purpose of this investigation was to examine the effects of a shift in carbon metabolism on phosphoenolpyruvate carboxylase and on NADP-malic enzyme in X. danguyi. Experiments were conducted to determine the diurnal patterns of enzyme activity and pH optima of both enzymes, as well as the approximate molecular mass, kinetic patterns, malate inhibition, and glucose-6-phosphate stimulation of phosphoenolpyruvate carboxylase. The two enzymes extracted from well-watered and water-stressed plants were similar in most parameters investigated; thus, CAM-idling appeared to be only a dampened form of CAM photosynthesis.
 ...
PMID:Shifts in the Carbon Metabolism of Xerosicyos danguyi H. Humb. (Cucurbitaceae) Brought About by Water Stress : II. Enzymology. 1666 54

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

The nature and sequence of metabolic events during phase II (early morning) Crassulacean acid metabolism in Opuntia erinacea var columbiana (Griffiths) L. Benson were characterized. Gas exchange measurements under 2 and 21% O(2) revealed increased O(2) inhibition of CO(2) fixation with progression of phase II. Malate and titratable acidity patterns indicated continued synthesis of C(4) acids for at least 30 minutes into the light period. Potential activities of phosphoenolpyruvate carboxylase (PEPC) and NADP-malic enzyme exhibited little change during phase II, while light activation of NADP-malate dehydrogenase, pyruvate, orthophosphate dikinase, and ribulose-1,5-bisphosphate carboxylase was apparent. Short-term (14)CO(2) fixation experiments showed that the per cent of (14)C incorporated into C(4) acids decreased while incorporation into other metabolites increased with time. PEPC exhibited increased sensitivity to 2 millimolar malate, and the K(i)(malate) for PEPC decreased markedly with time. Sensitivity of PEPC to malate inhibition was considerably greater at pH 7.5 than at 8.0. The results indicate that decarboxylation and synthesis of malate occur simultaneously during the early morning period, and that phase II acid metabolism is not limited by CO(2) diffusion through stomata. With progression of phase II, CO(2) fixation by PEPC decreases while fixation by ribulose-1,5-bisphosphate carboxylase increases.
 ...
PMID:Characterization of Early Morning Crassulacean Acid Metabolism in Opuntia erinacea var Columbiana (Griffiths) L. Benson. 1666 2

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.
 ...
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.
 ...
PMID:Enzymic and Photosynthetic Characteristics of Reciprocal F(1) Hybrids of Flaveria pringlei (C(3)) and Flaveria brownii (C(4)-Like Species). 1666 69

Light microscopic examination of leaf cross-sections showed that Flaveria brownii A. M. Powell exhibits Kranz anatomy, in which distinct, chloroplast-containing bundle sheath cells are surrounded by two types of mesophyll cells. Smaller mesophyll cells containing many chloroplasts are arranged around the bundle sheath cells. Larger, spongy mesophyll cells, having fewer chloroplasts, are located between the smaller mesophyll cells and the epidermis. F. brownii has very low CO(2) compensation points at different O(2) levels, which is typical of C(4) plants, yet it does show about 4% inhibition of net photosynthesis by 21% O(2) at 30 degrees C. Protoplasts of the three photosynthetic leaf cell types were isolated according to relative differences in their buoyant densities. On a chlorophyll basis, the activities of phosphoenolpyruvate carboxylase and pyruvate, Pi dikinase (carboxylation phase of C(4) pathway) were highest in the larger mesophyll protoplasts, intermediate in the smaller mesophyll protoplasts, and lowest, but still present, in the bundle sheath protoplasts. In contrast, activities of ribulose 1,5-bisphosphate carboxylase, other C(3) cycle enzymes, and NADP-malic enzyme showed a reverse gradation, although there were significant activities of these enzymes in mesophyll cells. As indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the banding pattern of certain polypeptides of the total soluble proteins from the three cell types also supported the distribution pattern obtained by activity assays of these enzymes. Analysis of initial (14)C products in whole leaves and extrapolation of pulse-labeling curves to zero time indicated that about 80% of the CO(2) is fixed into C(4) acids (malate and aspartate), whereas about 20% of the CO(2) directly enters the C(3) cycle. This is consistent with the high activity of enzymes for CO(2) fixation by the C(4) pathway and the substantial activity of enzymes of the C(3) cycle in the mesophyll cells. Therefore, F. brownii appears to have some capacity for C(3) photosynthesis in the mesophyll cells and should be considered a C(4)-like species.
 ...
PMID:Photosynthesis in Flaveria brownii, a C(4)-Like Species: Leaf Anatomy, Characteristics of CO(2) Exchange, Compartmentation of Photosynthetic Enzymes, and Metabolism of CO(2). 1666 39

Activities and subunit levels of three C(4) enzymes were determined for F(1) hybrids between C(4) and C(3)-C(4)Flaveria species. For phosphoenolpyruvate carboxylase and pyruvate orthophosphate, dikinase, enzyme amounts in the hybrids were close to the mid-parent means. However, activity and subunit levels of NADP-malic enzyme were approximately one-half the mid-parent mean.
 ...
PMID:Inheritance of c(4) enzymes associated with carbon fixation in flaveria species. 1666 42

Photosynthesis was examined in leaves of Flaveria brownii A. M. Powell, grown under either 14% or 100% full sunlight. In leaves of high light grown plants, the CO(2) compensation point and the inhibition of photosynthesis by 21% O(2) were significantly lower, while activities of ribulose 1,5-bisphosphate carboxylase/oxygenase and various C(4) cycle enzymes were considerably higher than those in leaves grown in low light. Both the CO(2) compensation point and the degree of O(2) inhibition of apparent photosynthesis were relatively insensitive to the light intensity used during measurements with plants from either growth conditions. Partitioning of atmospheric CO(2) between Rubisco of the C(3) pathway and phosphoenolpyruvate carboxylase of the C(4) cycle was determined by exposing leaves to (14)CO(2) for 3 to 16 seconds, and extrapolating the labeling curves of initial products to zero time. Results indicated that approximately 94% of the CO(2) was fixed by the C(4) cycle in high light grown plants, versus approximately 78% in low light grown plants. Thus, growth of F. brownii in high light increased the expressed level of C(4) photosynthesis. Consistent with the carbon partitioning patterns, photosynthetic enzyme activities (on a chlorophyll basis) in protoplasts from leaves of high light grown plants showed a more C(4)-like pattern of compartmentation. Pyruvate, Pi dikinase and phosphoenolpyruvate carboxylase were more enriched in the mesophyll cells, while NADP-malic enzyme and ribulose 1,5-bisphosphate carboxylase/oxygenase were relatively more abundant in the bundle sheath cells of high light than of low light grown plants. Thus, these results indicate that F. brownii has plasticity in its utilization of different pathways of carbon assimilation, depending on the light conditions during growth.
 ...
PMID:Photosynthetic Plasticity in Flaveria brownii: Growth Irradiance and the Expression of C(4) Photosynthesis. 1666 75

Transfer of C(4) photosynthetic traits was studied through hybridization of Flaveria trinervia (Spreng.) Mohr (C(4)) and Flaveria brownii A.M. Powell (C(4)-like) with Flaveria linearis Lag. (C(3)-C(4)) and the C(3) species Flaveria pringlei Gandoger (C(3)). Fertility was low, based on irregular chromosome pairing and low pollen stainability, except in F. brownii x F. linearis which had bivalent pairing and 76% stainable pollen. Hybrids had apparent photosynthesis values of 71 to 148% of the midparental means, while the CO(2) compensation concentration was similar to the C(4) or C(4)-like parent, except in hybrids having the C(3) species F. pringlei as a parent. Inhibition of apparent photosynthesis by O(2), and phosphoenolpyruvate carboxylase and NADP-malic enzyme activities and subunit levels in the hybrids were closer to the C(3) or C(3)-C(4) parent. The species F. brownii and F. trinervia were equal in their capacity to transfer reduced O(2) inhibition of AP and CO(2) compensation concentration values to hybrids with F. linearis (C(3)-C(4)), although hybrids with F. trinervia had higher PEPC activity. The O(2) inhibition of AP was correlated with the logarithm of activities of phosphoenolpyruvate carboxylase (r = -0.95) and NADP-malic enzyme (r = -0.87). These results confirm that C(4) traits can be transferred by hybridization of C(3)-C(4) and C(4) or C(4)-like species, with a higher degree of C(4) photosynthesis than exists in C(3)-C(4) species, and at least in F. brownii x F. linearis, fertile progeny are obtained.
 ...
PMID:Transfer of C(4) Photosynthetic Characters through Hybridization of Flaveria Species. 1666 62


<< Previous 1 2 3 4 5 6 7 8 9 Next >>