Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P00790 (PGA)
 2,475 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The (12)CO2- and (14)CO2-exchange of illuminated corn leaf discs were measured at normal (21%) and low (1%) oxygen. After periods of exposure to (14)CO2 or to (14)CO2 followed by (12)CO2, the discs were killed and the specific activities of some metabolites were determined. At both O2 concentrations the specific activity of 3-PGA increased and decreased rapidly during the first 5 min of (14)CO2-feeding or (12)CO2-flushing but did not equilibrate with that of the CO2 in the assimilation chamber even after 15 min. The specific activity of aspartic acid also showed bimodal kinetics during both feeding and flushing. The specific activities of 3-phosphoglyceric acid (3-PGA), aspartic acid and alanine were higher at 1% O2 than at 21% O2, but glycine and serine were lower in specific activity at 1% O2. The results are in agreement with the proposed initial fixation of CO2 into C4-dicarboxylic acids and subsequent transfer of this carbon to 3-PGA. Indirect evidence supports the idea that at 21% O2, CO2 was produced by the corn leaf discs in the light and was refixed into C4-dicarboxylic acids. At 1% O2, the photorespiratory process could also have been active although the flux of carbon through the glycolate pathway was probably smaller than at 21% O2.
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PMID:Changes in specific radioactivities of corn-leaf metabolites during photosynthesis in (14)CO 2 and (12)CO 2 at normal and low oxygen. 2444 50

Sunflower (Helianthus annuus L.) leaf discs were exposed to (14)CO2 or (14)CO2 followed by (12)CO2 in an open gas-exchange system with incoming gas of approximately 400 ppm CO2 and either 21% or 1% O2. The (14)CO2 and (12)CO2 gas-exchange of the leaf discs were measured, and the specific activities of several metabolites were determined after different lengths of time. The rate of CO2 efflux by the leaf discs was ca. 20% of the net photosynthetic rate at 21% O2 but no CO2 efflux could be detected at 1% O2. At both O2 concentrations the specific activity of 3-phosphoglyceric acid (3-PGA) increased and decreased rapidly for the first 5 min, and then more slowly during (14)CO2 feeding and (12)CO2 flushing. At 21% O2, glycine, serine and alanine changed more slowly in specific activity than 3-PGA and at 1% O2 their specific activities were much lower than at 21% O2. The results at both O2 concentrations indicated that the glycolate pathway compounds were not derived solely from Calvin-cycle intermediates. At 1% O2 the flux of carbon from the immediate fixation products was inhibited and serine was at least partially produced from a precursor of higher specific activity than glycine, although the glycolate pathway may have been active even at 1% O2. The difference between the specific activities of 3-PGA and the feeding gases could be explained by the recycling of C from the glycolate pathway.
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PMID:Changes in specific radioactivities of sunflower leaf metabolites during photosynthesis in (14)CO 2 and (12)CO 2 at normal and low oxygen. 2444 51

Sunflower (Helianthus annuus L.) leaf discs were exposed to (14)CO2 or (14)CO2 followed by (12)CO2 at 21% O2 and three different CO2 concentrations. After intervals of up to 15 min, the specific activity of some photosynthetic intermediates was determined. At all CO2 concentrations, the specific activity of 3-phosphoglyceric acid (3-PGA) increased most rapidly and after 15 min of (14)CO2 feeding was 92% (967 ppm CO2), 87% (400 ppm CO2) and 53% (115 ppm CO2) of CO2 supplied to the assimilation chamber. The specific activity of glycine, serine and the photorespiratory CO2 was similar at all CO2 concentrations, in aggreement with their proposed close metabolic relationship in the glycolate pathway. However, the kinetics of serine and glycine labelling suggested that serine was not totally derived from glycine. Because the specific activity of these glycolate-pathway intermediates was very differnet from that of 3-PGA at all CO2 concentrations, not all of the carbon traversing this pathway came directly from the Calvin cycle. The non-equilibration of the 3-PGA with the feeding gas reflects the recycling of C from the glycolate pathway into the photosynthetic reduction cycle. Measurements of the rates of CO2 evolution in the light and estimates of the C flux through the glycolate pathway suggest that the photorespiratory activity was high and similar at 115 ppm CO2 and 400 ppm CO2 but inhibited at 967 ppm CO2.
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PMID:Changes in specific radioactivity of sunflower leaf metabolites during photosynthesis in (14)CO 2 and (12)CO 2 at three concentrations of CO 2. 2444 99

Suspensions of Chlorella vulgaris were allowed to photosynthesise with two concentrations of (14)CO2 (101 and 543 ppm) in 80% oxygen, and the incorporation of (14)C into glycolate and 3-phosphoglyceric acid (3-PGA) was followed. The relative specific activity (RSA) of the glycolate formed at both CO2 concentrations decreased initially and then increased slowly. The RSA of glycolate was much lower when the suspension photosynthesised in 101 ppm (14)CO2 compared to 543 ppm. The RSA of 3-PGA was nearly always lower than that of glycolate and the results suggest that refixed dark respiratory CO2 or respiratory 3-PGA, or both, substantially contribute to the total 3-PGA in the algae. It is concluded that glycolate is formed from recent photosynthate as well as from storage material, but the relative contribution of these substrates depends on the conditions under which the algae are grown, as well as those obtaining at the time of glycolate excretion.
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PMID:On the formation of glycolate in photosynthesizing Chlorella using a new gas-liquid chromatography method. 2444 29

Postillumination CO2 fixation by wheat leaves was studied following light-limited photosynthetic conditions. Dark CO2 fixation showed two phases differing by their rates of CO2 uptake and carbon metabolism. These two phases are related to preillumination light flux density. During the first 30s of darkness, assimilated CO2 was found in PGA, alanine, malate and aspartate. After 5 min of darkness, it was additionally found in phosphorylated sugars.The lack of labelling of glycolate pathway intermediates shows that the Calvin cycle cannot run in the dark.The synthesized compounds indicate that reducing power but not ATP is available after turning the light off. This observation suggests that during pre-illumination, when light strictly limits photosynthesis, ATP supply would be the first limiting factor.
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PMID:Postillumination CO2 fixation by wheat leaves. 2447 Feb 29

1. The photoreduction of K3[Fe(CN)6] by isolated and sonicated spinach chloroplasts is increased by SO 3 (--) (concentrations tested: 0.25-5 mM). This stimulation increases with SO 3 (--) concentrations from 0.25-3 mM. The ferricyanide-reduction with SO 3 (--) is inhibited by DCMU (10(-6)M) to about 90%. Inhibition of the photoreduction by pretreatment of the chloroplasts with Tris-buffer is compensated by increasing concentrations of SO 3 (--) (tested up to 3 mM). 2. The photoreduction of NADP in isolated chloroplasts is also enhanced by SO 3 (--) (concentrations tested: 0.25-3.0 mM). It is completely inhibited by DCMU (10(-6)M). In contrast to the results with ferricyanide as electron acceptor, SO 3 (--) does not overcome the inhibition of NADP reduction caused by pretreatment of the chloroplasts with Tris-buffer. 3. In illuminated isolated chloroplasts SO 3 (--) concentrations <1 mM do not alter the ATP-concentration, concentrations>1 mM decrease it. 4. The photosynthetic fixation of (14)CO2 by isolated chloroplasts is increased by SO 3 (--) concentrations <1 mM, but decreased by concentrations>1 mM. In total (14)CO2 fixed, at stimulating concentrations (0.25 and 0.5 mM SO 3 (--) ), the relative amount of sugar-monophosphates is increased, whereas that of sugardiphosphates and of PGA is decreased. 5. It is proposed that these specific effects on photosynthetic processes help to explain the well known fact that photosynthetic gas exchange and the yield of plants are stimulated by low doses of SO2.
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PMID:[Stimulation of hill-reaction and CO2 fixation in isolated spinach chloroplasts by low concentrations of SO 3 (--)]. 2447 59

Following a period of steady state photosynthesis, in air, maize leaves were illuminated in a CO2-free atmosphere consisting of N2 or N2-O2 (80-20, v/v).Isotopic techniques have been used for the measurement in cells of pool sizes of some phosphorylated intermediates and for the study of the turn-over of these compounds.In N2 atmosphere and white light, a rapid decrease of the PGA level and an accumulation of Ru 1-5 P2 are observed, whereas DHAP and Fru 1-6 P2 levels remain high. With (32)P feeding in short-time experiments, Ru 1-5 P2, ATP and ADP are highly labelled, and there is a low but significant labelling of PGA and DHAP. Our interpretation is that basic reactions of the CALVIN cycle are occurring: phosphorylation of Ru 5 P to Ru 1-5 P2 (phosphorylating step), carboxylation of Ru 1-5 P2 to PGA (the CO2 belongs to an intracellular pool of unknown nature), reduction of PGA to trioses phosphates (reductive step), regeneration of the CO2 acceptor via the synthesis of Ru 5P (regenerative step). In N2 atmosphere the second step is the limiting one because of the low intracellular CO2 level; the consequence is an increase in the amount of the CO2 acceptor and of the compounds belonging to the regenerative step.When leaves have been treated with CMU before an illumination (white light) in N2 atmosphere, increased levels of PGA are observed as compared with the preceding experiments, whereas those of DHAP and Fru 1-6 P2 are lower; in short-time experiments, the PGA is labelled to a much greater extent than Ru 1-5 P2 and DHAP. In this case the limiting steps of the CALVIN cycle are: a) the reductive step, affecting the levels of the intermediates of the regenerative step: DHAP, Fru 1-6 P2 and Ru 5P. b) the phosphorylative step, because of the inhibition of the non-cyclic photophosphorylations: there is a decrease of the ATP cellular level. In N2 atmosphere a far-red illumination has the same effect on pool-sizes and labelling of compounds as CMU in white light, owing to the inhibition of the reducing power.In N2-O2 atmosphere (white light), the PGA level is higher than in N2 atmosphere; the effect of O2 is discussed (stimulation of the oxydative pentose phosphate cycle?).A physiological part played by the important reservoir of PGA accumulating in vivo, especially in far-red light, is suggested in "Discussion".
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PMID:[Metabolism of some phosphorylated compounds and photophosphorylation in Maize leaves]. 2451 86


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