Pyrophosphate as an alternative energy currency in plants

In the conditions of [Mg2+] elevation that occur, in particular, under low oxygen stress and are the consequence of the decrease in [ATP] and increase in [ADP] and [AMP], pyrophosphate (PPi) can function as an alternative energy currency in plant cells. In addition to its production by various metabolic pathways, PPi can be synthesized in the combined reactions of pyruvate, phosphate dikinase (PPDK) and pyruvate kinase (PK) by so-called PK/PPDK substrate cycle, and in the reverse reaction of membrane-bound H+-pyrophosphatase, which uses the energy of electrochemical gradients generated on tonoplast and plasma membrane. The PPi can then be consumed in its active forms of MgPPi and Mg2PPi by PPi-utilizing enzymes, which require an elevated [Mg2+]. This ensures a continuous operation of glycolysis in the conditions of suppressed ATP synthesis, keeping metabolism energy efficient and less dependent on ATP.

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Compartmentation of enzymes in a microbody, the glycosome, is essential in Trypanosoma brucei

Journal of Cell Science ◽

10.1242/jcs.115.13.2651 ◽

2002 ◽

Vol 115 (13) ◽

pp. 2651-2658

Author(s):

Cristina Guerra-Giraldez ◽

Luis Quijada ◽

Christine E. Clayton

Keyword(s):

Rna Interference ◽

Trypanosoma Brucei ◽

Metabolic Pathways ◽

Mammalian Cells ◽

Atp Synthesis ◽

Bloodstream Form ◽

Matrix Proteins ◽

Selective Media ◽

Atp Generation ◽

Membrane Bound

All kinetoplastids contain membrane-bound microbodies known as glycosomes,in which several metabolic pathways including part of glycolysis are compartmentalized. Peroxin 2 is essential for the import of many proteins into the microbodies of yeasts and mammals. The PEX2 gene of Trypanosoma brucei was identified and its expression was silenced by means of tetracycline-inducible RNA interference. Bloodstream-form trypanosomes, which rely exclusively on glycolysis for ATP generation, died rapidly upon PEX2 depletion. Insect-form (procyclic) trypanosomes do not rely solely on glycolysis for ATP synthesis. PEX2 depletion in procyclic forms resulted in relocation of most tested matrix proteins to the cytosol, and these mutants also died. Compartmentation of microbody enzymes is therefore essential for survival of bloodstream and procyclic T. brucei. In contrast, yeasts and cultured mammalian cells grow normally in the absence of peroxisomal membranes unless placed on selective media.

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Magnesium and cell energetics in plants under anoxia

Biochemical Journal ◽

10.1042/bj20110213 ◽

2011 ◽

Vol 437 (3) ◽

pp. 373-379 ◽

Cited By ~ 30

Author(s):

Abir U. Igamberdiev ◽

Leszek A. Kleczkowski

Keyword(s):

Energy Efficient ◽

Alternative Energy ◽

Active Form ◽

Stress Conditions ◽

Signalling Pathways ◽

Concomitant Increase ◽

Pyruvate Phosphate Dikinase ◽

Calcium Dependent ◽

Alternative Energy Source ◽

Apparent Equilibrium

Stress conditions (e.g. anoxia) frequently result in a decrease of [ATP] and in an increase of [ADP] and [AMP], with a concomitant increase of [Mg2+] and other cations, e.g. Ca2+. The elevation of [Mg2+] is linked to the shift in the apparent equilibrium of adenylate kinase. As a result, enzymes that use Mg2+ as a cofactor are activated, Ca2+ activates calcium-dependent signalling pathways, and PPi can serve as an alternative energy source in its active form of MgPPi or Mg2PPi. Under anoxic conditions in plants, an important source of PPi may come as a result of combined reactions of PK (pyruvate kinase) and PPDK (pyruvate, phosphate dikinase). The PPi formed in the PPDK/PK cycle ignites glycolysis in conditions of low [ATP] by involving PPi-dependent reactions. This saves ATP and makes metabolism under stress conditions more energy efficient.

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What are hemoglobins doing in plants?

Canadian Journal of Botany ◽

10.1139/b98-057 ◽

1998 ◽

Vol 76 (5) ◽

pp. 707-712 ◽

Cited By ~ 8

Author(s):

Robert D Hill

Keyword(s):

Plant Community ◽

Plant Cells ◽

Gold Medal ◽

Plant Biology ◽

Flooding Tolerance ◽

Energy Status ◽

Low Oxygen ◽

Oxygen Stress ◽

Oxygen Dissociation ◽

Oxygen Tensions

Within the last 3-4 years, evidence has accumulated to indicate that hemoglobin proteins exist widely in the plant community. This review presents some of the evidence to support this view and describes some of the properties of a barley hemoglobin. Barley hemoglobin has a strong avidity for oxygen, having an oxygen dissociation constant for oxyhemoglobin of 3 nmol L-1. It is induced under low oxygen tensions, with the induction regulated by ATP, or some consequence of ATP action. Experiments with transformed maize cells indicate that hemoglobin acts to improve the energy status of plant cells under low oxygen stress. It is postulated that hemoglobin acts as an oxygenase in plants. The review is a consequence of a CSPP Gold Medal Presentation at the Plant Biology 1997 Meeting in Vancouver, B.C.Key words: nonsymbiotic hemoglobins, hypoxia, barley, flooding tolerance.

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Dynamic changes of antioxidants and fermentative metabolites in apple peel in relation to storage, controlled atmosphere, and initial low oxygen stress

Scientia Horticulturae ◽

10.1016/j.scienta.2021.110312 ◽

2021 ◽

Vol 288 ◽

pp. 110312

Author(s):

Marina Buccheri ◽

Valentina Picchi ◽

Maurizio Grassi ◽

Davide Gandin ◽

Giulia Bianchi ◽

...

Keyword(s):

Controlled Atmosphere ◽

Low Oxygen ◽

Dynamic Changes ◽

Oxygen Stress ◽

Apple Peel

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Protein Import into Hydrogenosomes of Trichomonas vaginalis Involves both N-Terminal and Internal Targeting Signals: a Case Study of Thioredoxin Reductases

Eukaryotic Cell ◽

10.1128/ec.00206-08 ◽

2008 ◽

Vol 7 (10) ◽

pp. 1750-1757 ◽

Cited By ~ 35

Author(s):

Marek Mentel ◽

Verena Zimorski ◽

Patrick Haferkamp ◽

William Martin ◽

Katrin Henze

Keyword(s):

Trichomonas Vaginalis ◽

Protein Import ◽

Atp Synthesis ◽

Antioxidant Systems ◽

Low Oxygen ◽

Oxygen Sensitive ◽

Targeting Signal ◽

Targeting Signals ◽

Thioredoxin Reductases

ABSTRACT The parabasalian flagellate Trichomonas vaginalis harbors mitochondrion-related and H2-producing organelles of anaerobic ATP synthesis, called hydrogenosomes, which harbor oxygen-sensitive enzymes essential to its pyruvate metabolism. In the human urogenital tract, however, T. vaginalis is regularly exposed to low oxygen concentrations and therefore must possess antioxidant systems protecting the organellar environment against the detrimental effects of molecular oxygen and reactive oxygen species. We have identified two closely related hydrogenosomal thioredoxin reductases (TrxRs), the hitherto-missing component of a thioredoxin-linked hydrogenosomal antioxidant system. One of the two hydrogenosomal TrxR isoforms, TrxRh1, carried an N-terminal extension resembling known hydrogenosomal targeting signals. Expression of hemagglutinin-tagged TrxRh1 in transfected T. vaginalis cells revealed that its N-terminal extension was necessary to import the protein into the organelles. The second hydrogenosomal TrxR isoform, TrxRh2, had no N-terminal targeting signal but was nonetheless efficiently targeted to hydrogenosomes. N-terminal presequences from hydrogenosomal proteins with known processing sites, i.e., the alpha subunit of succinyl coenzyme A synthetase (SCSα) and pyruvate:ferredoxin oxidoreductase A, were investigated for their ability to direct mature TrxRh1 to hydrogenosomes. Neither presequence directed TrxRh1 to hydrogenosomes, indicating that neither extension is, by itself, sufficient for hydrogenosomal targeting. Moreover, SCSα lacking its N-terminal extension was efficiently imported into hydrogenosomes, indicating that this extension is not required for import of this major hydrogenosomal protein. The finding that some hydrogenosomal enzymes require N-terminal signals for import but that in others the N-terminal extension is not necessary for targeting indicates the presence of additional targeting signals within the mature subunits of several hydrogenosome-localized proteins.

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