Photorespiratory nitrogen cycle

Keys, A. J.; Bird, I. F.; Cornelius, M. J.; Lea, Peter J.; Wallsgrove, R. M.; Miflin, B. J.

doi:10.1038/275741a0

Cited by 504 publications

(266 citation statements)

References 15 publications

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“…The events that follow oxygenation of 1 tool RuP 2 include release and refixation of 0.5 mol ammonia (Woo et al 1978;Keys et al 1978), a sequence which requires the use of 2Fd-(reduced ferredoxin) per NH +. The PCO cycle therefore appears to have an additional cost of 0.5 NADPH for each 0.5 NH~-refixed.…”

Section: (5)mentioning

confidence: 99%

A biochemical model of photosynthetic CO2 assimilation in leaves of C3 species

Farquhar

Caemmerer

Berry

1980

Planta

7,565

6,691

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Abstract.Various aspects of the biochemistry of photosynthetic carbon assimilation in C3 plants are integrated into a form compatible with studies of gas exchange in leaves. These aspects include the kinetic properties of ribulose bisphosphate carboxylaseoxygenase; the requirements of the photosynthetic carbon reduction and photorespiratory carbon oxidation cycles for reduced pyridine nucleotides; the dependence of electron transport on photon flux and the presence of a temperature dependent upper limit to electron transport. The measurements of gas exchange with which the model outputs may be compared include those of the temperature and partial pressure of CO2(p(CO2) ) dependencies of quantum yield, the variation of compensation point with temperature and partial pressure of O2(p(O2)), the dependence of net CO 2 assimilation rate on p(CO2) and irradiance, and the influence of p(CO2) and irradiance on the temperature dependence of assimilation rate.

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Section: (5)mentioning

confidence: 99%

A biochemical model of photosynthetic CO2 assimilation in leaves of C3 species

Farquhar

Caemmerer

Berry

1980

Planta

7,565

6,691

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“…In bacteria, there is a coordinated regulation of activity among the GCV, the PDC and the 2-oxoglutarate dehydrogenase complex. In yeast, such flux through the GCV-SHMT system is required for both the synthesis of serine from glycine and the use of glycine as the sole nitrogen source; in plants, the GCV is the enzymatic system that deals with the large quantities of glycine resulting from major metabolic reactions in illuminated leaves [25]. However, the importance of the GCV-SHMT system and the serine-glycine flux in pathogenic micro-organisms is largely unknown at present.…”

Section: The Gcv and Pathogenesismentioning

confidence: 99%

A glycine-cleavage complex as part of the folate one-carbon metabolism of Plasmodium falciparum

Salcedo

Sims

Hyde

2005

Trends in Parasitology

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The glycine-cleavage complex (GCV) and serine hydroxymethyltransferase represent the two systems of one-carbon transfer that are employed in the biosynthesis of active folate cofactors in eukaryotes. Although the understanding of this area of metabolism in Plasmodium falciparum is still at an early stage, we discuss evidence that genes and transcription products of the GCV are present and expressed in this parasite. The potential role of the GCV and its relevance to the life cycle and pathogenesis of the malaria erythrocytic stages are also considered. According to its expression profile, the GCV seems to be particularly active in gametocytes. The GCV enzyme dihydrolipoamide dehydrogenase has two isoforms encoded by two different genes. It has been demonstrated recently that both genes are functional, with one of them identified as being part of a pyruvate dehydrogenase complex that is present exclusively in the apicoplast of Plasmodium species. The other isoform probably forms part of the Plasmodium GCV. The GCV is the first enzyme complex involved in folate metabolism in this parasite that can be assumed, with a good degree of certainty, to be located in the mitochondria. Synthesis and use of the one-carbon unit in folateThe glycine-cleavage complex (GCV) and serine hydroxymethyltransferase [SHMT, also called glycine hydroxymethyltransferase (EC 2.1.2.1)] form part of the folic acid biosynthesis pathway, generating one-carbon units from cleavage of the small amino acids glycine and serine, respectively. These one-carbon units are transferred onto folate coenzymes that carry and donate them, primarily for the synthesis of pyrimidines [e.g. thymidylate (5′-TMP)] and methionine in the malaria parasite [1]. SHMT can reversibly interconvert glycine and serine, and glycine itself is a precursor of the synthesis of glutathione, tryptophan and phospholipids in eukaryotes [2]. The importance of the ubiquitous GCV enzymatic complex is exemplified by its role in essential homeostatic processes. For instance, the synthesis of glutathione to maintain the redox balance of the erythrocyte plasma membrane needs an active but regulated glycine supply [3], the mitochondrial processing of high concentrations of phosphorespiration glycine in plants relies on plant GCVs [4], and a dys-functional GCV in humans caused by specific point mutations is related to an inherited condition known as nonketotic hyperglycinemia or glycine encephalopathy [5].Whereas serine, through the reaction catalysed by SHMT, is the main source of one-carbon units in the cytoplasm, glycine is equally relevant in the mitochondrion, and the GCV . The activation and use of folate depend on covalent linkage to a one-carbon unit -a byproduct of the balanced flux of carbon between serine and glycine -through SHMT and GCV, two independent but functionally related enzyme systems (Figure 1). The de novo production of fully reduced and glutamated (and, hence, functional) folate in Plasmodium falciparum is the result of the actions of six enzymatic activities...

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“…Tobacco leaves have very low levels of GDH transcript, protein, and activity compared with roots (Purnell et al, 2005) (Baum et al, 1996), the fact that [ 15 N]GABA accumulation in A63-NS leaves was only 7% of that in roots during the control treatment suggests that leaf [ 15 N]Glu concentration was relatively low. 1 within mesophyll cells (Keys et al, 1978). GS2 is crucial for the reassimilation of this NH 4 1 , because mutants lacking this enzyme accumulate NH 4 1 and die (Wallsgrove et al, 1987).…”

Section: Gdh Isoenzyme 1 In Roots Catabolizes Glumentioning

confidence: 99%

Tobacco Isoenzyme 1 of NAD(H)-Dependent Glutamate Dehydrogenase Catabolizes Glutamate in Vivo

Purnell

Botella

2006

Plant Physiol.

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Glutamate (Glu) dehydrogenase (GDH, EC 1.4.1.2-1.4.1.4) catalyzes in vitro the reversible amination of 2-oxoglutarate to Glu. The in vivo direction(s) of the GDH reaction in higher plants and hence the role(s) of this enzyme is unclear, a situation confounded by the existence of isoenzymes comprised totally of either GDH b-(isoenzyme 1) or a-(isoenzyme 7) subunits, as well as another five a-b isoenzyme permutations. To clarify the in vivo direction of the reaction catalyzed by GDH isoenzyme 1, [ 15 N]Glu was supplied to roots of two independent transgenic tobacco (Nicotiana tabacum) lines with increased isoenzyme 1 levels (S4-H and S49-H). The [ 15 N]ammonium (NH 4 1 ) accumulation rate in these lines was elevated approximately 65% compared with a null segregant control line, indicating that isoenzyme 1 catabolizes Glu in roots. Leaf glutamine synthetase (GS) was inhibited with a GS-specific herbicide to quantify any contribution by GDH toward photorespiratory NH 4 1 reassimilation. Transgenic line S49-H did not show enhanced resistance to the herbicide, indicating that the large pool of isoenzyme 1 in S49-H leaves was unable to compensate for GS and suggesting that isoenzyme 1 does not assimilate NH 4 1 in vivo.The intricate linkage of plant C and N metabolism requires constant balancing at the cellular level. Fundamentally, this involves orchestrating cellular levels of three metabolites: ammonium (NH 4

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Photorespiratory nitrogen cycle

Cited by 504 publications

References 15 publications

A biochemical model of photosynthetic CO2 assimilation in leaves of C3 species

A biochemical model of photosynthetic CO2 assimilation in leaves of C3 species

A glycine-cleavage complex as part of the folate one-carbon metabolism of Plasmodium falciparum

Tobacco Isoenzyme 1 of NAD(H)-Dependent Glutamate Dehydrogenase Catabolizes Glutamate in Vivo

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