scholarly journals Relationship between NH+4 Assimilation Rate and in Vivo Phosphoenolpyruvate Carboxylase Activity

1990 ◽  
Vol 94 (1) ◽  
pp. 284-290 ◽  
Author(s):  
Greg C. Vanlerberghe ◽  
Kathryn A. Schuller ◽  
Ronald G. Smith ◽  
Regina Feil ◽  
William C. Plaxton ◽  
...  
Keyword(s):  
Phosphoenolpyruvate Carboxylase ◽  
Assimilation Rate ◽  
Carboxylase Activity

Organic acid concentration is little controlled by phosphoenolpyruvate carboxylase activity in peach fruit

1999 ◽  
Vol 26 (6) ◽  
pp. 579 ◽  
Author(s):  
L. Svanella ◽  
M. Gaudillère ◽  
J. P. Gaudillère ◽  
A. Moing ◽  
R. Monet
Keyword(s):  
Organic Acid ◽  
Acid Concentration ◽  
Phosphoenolpyruvate Carboxylase ◽  
Prunus Persica ◽  
Carboxylase Activity ◽  
Acid Accumulation ◽  
Citrate Accumulation ◽  
Accumulation Phase

Changes in phosphoenolpyruvate carboxylase (PEPC) activity were studied during the fruit development of two peach cultivars (Prunus persica (L.) Batsch) with normal (‘Fantasia’) and low (‘Jalousia’) organic acid concentration. PEPC activities were measured in fruit mesocarp at two stages of development, corresponding to malate accumulation and citrate accumulation phases in ‘Fantasia’, respectively. In vitro activity, measured under optimal conditions, was significantly higher in ‘Fantasia’ than in ‘Jalousia’ during the malate accumulation phase but lower during the citrate accumulation phase. In vivo activity was estimated using 14CO2 labelling. The total incorporated radioactivity was higher in ‘Fantasia’ than in ‘Jalousia’ during the malate accumulation phase but lower during the citrate accumulation phase. During the malate accumulation phase, the partitioning of incorporated 14C into malate was significantly reduced in ‘Jalousia’ compared to ‘Fantasia’ after 20 min labelling. During the citrate accumulation phase, 14 C partitioning into malate was not significantly different between varieties, but partitioning into citrate was significantly reduced in ‘Jalousia’ compared to ‘Fantasia’. Therefore, PEPC activity does not seem to be the controlling step for the absence of organic acid accumulation in ‘Jalousia’ fruit. The other metabolic causes of the difference in organic acid accumulation are discussed; these may be connected with vacuolar storage.

Relationship Between Steady-State Gas Exchange, in vivo Ribulose Bisphosphate Carboxylase Activity and Some Carbon Reduction Cycle Intermediates in Raphanus sativus

1986 ◽  
Vol 13 (5) ◽  
pp. 669 ◽  
Author(s):  
SV Caemmerer ◽  
DL Edmondson
Keyword(s):  
Gas Exchange ◽  
Co2 Assimilation ◽  
Assimilation Rate ◽  
Carboxylase Activity ◽  
Bisphosphate Carboxylase ◽  
High Co2 ◽  
Co2 Assimilation Rate ◽  
Low Co2 ◽  
Pool Sizes

The relationships between CO2 assimilation rate, RuP2 carboxylase activity and sizes of the pools of ribulose 1,5-bisphosphate (RuP2) and 3-phosphoglyceric acid (PGA) were examined using a freeze clamp device to rapidly freeze sections of attached leaves of R. sativus which previously had gas-exchange measurements made on them. At high irradiance and ambient partial pressures of CO2 and O2, RuP2 carboxylase was fully active in vivo. Activity was less at very low CO2 pressures and at high CO2 pressures, particularly when combined with low O2 pressures. In vivo RuP2 carboxylase activity and both RuP2 and PGA pool sizes increased with increasing irradiance. RuP2 pool sizes were high at low CO2 pressures and decreased at high CO2 pressures. PGA pool sizes, on the other hand, were low at low CO2 and high at high CO2 pressures. A model of RuP2 carboxylase-oxygenase (Rubisco) kinetics is used to examine the quantitative relationship between in vivo RuP2 carboxylase activity, CO2 assimilation rate and RuP2 and PGA pools. The model predictions fit in vivo data, except at high CO2 pressures, if it is assumed that RuP2 does not bind tightly to the inactive enzyme form in vivo. It is shown that a large fraction of the RuP2 and PGA pools may be chelated by magnesium in the stroma and that the high RuP2 pools (e.g. at low irradiance) may represent an optimal concentration rather than be truly saturating. We conclude that RuP2 pool sizes above Rubisco site concentration do not necessarily indicate a Rubisco limitation of photosynthetic rate.

Regulation of soybean nodule phosphoenolpyruvate carboxylase in vivo

1996 ◽  
Vol 97 (3) ◽  
pp. 531-535 ◽  
Author(s):  
Carol Wadham ◽  
Heike Winter ◽  
Kathryn A. Schuller
Keyword(s):  
Phosphoenolpyruvate Carboxylase ◽  
Soybean Nodule

scholarly journals In vivo 13C MRS in the mouse brain at 14.1 Tesla and metabolic flux quantification under infusion of [1,6-13C2]glucose

2017 ◽  
Vol 38 (10) ◽  
pp. 1701-1714 ◽  
Author(s):  
Marta Lai ◽  
Bernard Lanz ◽  
Carole Poitry-Yamate ◽  
Jackeline F Romero ◽  
Corina M Berset ◽  
...  
Keyword(s):  
Mouse Brain ◽  
Metabolic Flux ◽  
Direct Detection ◽  
Tricarboxylic Acid Cycle ◽  
Quantitative Information ◽  
Glutamine Metabolism ◽  
Resonance Spectroscopy ◽  
Flux Analysis ◽  
Carboxylase Activity

In vivo 13C magnetic resonance spectroscopy (MRS) enables the investigation of cerebral metabolic compartmentation while, e.g. infusing 13C-labeled glucose. Metabolic flux analysis of 13C turnover previously yielded quantitative information of glutamate and glutamine metabolism in humans and rats, while the application to in vivo mouse brain remains exceedingly challenging. In the present study, 13C direct detection at 14.1 T provided highly resolved in vivo spectra of the mouse brain while infusing [1,6-13C2]glucose for up to 5 h. 13C incorporation to glutamate and glutamine C4, C3, and C2 and aspartate C3 were detected dynamically and fitted to a two-compartment model: flux estimation of neuron-glial metabolism included tricarboxylic acid cycle (TCA) flux in astrocytes (Vg = 0.16 ± 0.03 µmol/g/min) and neurons (VTCAn = 0.56 ± 0.03 µmol/g/min), pyruvate carboxylase activity (VPC = 0.041 ± 0.003 µmol/g/min) and neurotransmission rate (VNT = 0.084 ± 0.008 µmol/g/min), resulting in a cerebral metabolic rate of glucose (CMRglc) of 0.38 ± 0.02 µmol/g/min, in excellent agreement with that determined with concomitant 18F-fluorodeoxyglucose positron emission tomography (18FDG PET).We conclude that modeling of neuron-glial metabolism in vivo is accessible in the mouse brain from 13C direct detection with an unprecedented spatial resolution under [1,6-13C2]glucose infusion.

Phosphoenolpyruvate carboxylase during grape berry development: protein level, enzyme activity and regulation

2000 ◽  
Vol 27 (3) ◽  
pp. 221 ◽  
Author(s):  
Paraskevi Diakou ◽  
Laurence Svanella ◽  
Philippe Raymond ◽  
Jean-Pierre Gaudillère ◽  
Annick Moing
Keyword(s):  
Malic Acid ◽  
Protein Level ◽  
Phosphoenolpyruvate Carboxylase ◽  
Phosphorylation Site ◽  
Acid Synthesis ◽  
Grape Berry ◽  
Vitis Vinifera L ◽  
Normal Acid

The protein level and regulation of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31, involved in malic acid synthesis) was studied during the fruit development of two grape (Vitis vinifera L.) varieties, ‘Cabernet Sauvignon’ and ‘Gora Chirine’, with berries of normal and low organic acid content, respectively. The protein level and in vitro activity were higher in the low-acid variety than in the normal-acid variety for most stages. In vivo PEPC activity, measured using 14 CO2 labelling, was significantly higher in the low-acid variety than in the normal-acid variety about 1 week before and 1 week after veraison (the day which corresponds to the onset of ripening). However, partitioning into malate was the same for both varieties. Antibodies raised against the N-terminal part of SorghumPEPC recognised the grape berry PEPC, indicating the presence of the consensus phosphorylation site involved in PEPC regulation. PEPC phosphorylation status was estimated by studying sensitivity to pH and malate. Grape berry PEPC appeared more sensitive to low pH and malate during ripening (IC50 malate, 0.2–0.7 mM) compared to during the earlier stages of development (IC50 malate, 1.2–2 mM) for both varieties. Therefore, in the normal-acid variety, PEPC seems to participate in controlling malic acid accumulation but does not seem to control the differences in malic acid concentration observed between the two varieties.

The remarkable diversity of plant PEPC (phosphoenolpyruvate carboxylase): recent insights into the physiological functions and post-translational controls of non-photosynthetic PEPCs

2011 ◽  
Vol 436 (1) ◽  
pp. 15-34 ◽  
Author(s):  
Brendan O'Leary ◽  
Joonho Park ◽  
William C. Plaxton
Keyword(s):  
Phosphoenolpyruvate Carboxylase ◽  
Tricarboxylic Acid Cycle ◽  
Critical Role ◽  
Subcellular Location ◽  
Serine Phosphorylation ◽  
Regulatory Subunit ◽  
Physiological Functions ◽  
Intrinsically Disordered ◽  
Class 1

PEPC [PEP (phosphoenolpyruvate) carboxylase] is a tightly controlled enzyme located at the core of plant C-metabolism that catalyses the irreversible β-carboxylation of PEP to form oxaloacetate and Pi. The critical role of PEPC in assimilating atmospheric CO2 during C4 and Crassulacean acid metabolism photosynthesis has been studied extensively. PEPC also fulfils a broad spectrum of non-photosynthetic functions, particularly the anaplerotic replenishment of tricarboxylic acid cycle intermediates consumed during biosynthesis and nitrogen assimilation. An impressive array of strategies has evolved to co-ordinate in vivo PEPC activity with cellular demands for C4–C6 carboxylic acids. To achieve its diverse roles and complex regulation, PEPC belongs to a small multigene family encoding several closely related PTPCs (plant-type PEPCs), along with a distantly related BTPC (bacterial-type PEPC). PTPC genes encode ~110-kDa polypeptides containing conserved serine-phosphorylation and lysine-mono-ubiquitination sites, and typically exist as homotetrameric Class-1 PEPCs. In contrast, BTPC genes encode larger ~117-kDa polypeptides owing to a unique intrinsically disordered domain that mediates BTPC's tight interaction with co-expressed PTPC subunits. This association results in the formation of unusual ~900-kDa Class-2 PEPC hetero-octameric complexes that are desensitized to allosteric effectors. BTPC is a catalytic and regulatory subunit of Class-2 PEPC that is subject to multi-site regulatory phosphorylation in vivo. The interaction between divergent PEPC polypeptides within Class-2 PEPCs adds another layer of complexity to the evolution, physiological functions and metabolic control of this essential CO2-fixing plant enzyme. The present review summarizes exciting developments concerning the functions, post-translational controls and subcellular location of plant PTPC and BTPC isoenzymes.

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