Mitochondrial transporter responsiveness and metabolic flux homeostasis in postischemic hearts

1999 ◽  
Vol 277 (3) ◽  
pp. H866-H873 ◽  
Author(s):  
J. Michael O’Donnell ◽  
Lawrence T. White ◽  
E. Douglas Lewandowski
Keyword(s):  
Redox State ◽  
Metabolic Flux ◽  
Tca Cycle ◽  
Tricarboxylic Acid ◽  
Stunned Myocardium ◽  
Mitochondrial Transporter ◽  
Metabolite Exchange ◽  
Stimulation Of ◽  
Shuttle Response

The transport of metabolites between mitochondria and cytosol via the α-ketoglutarate-malate carrier serves to balance flux between the two spans of the tricarboxylic acid (TCA) cycle but is reduced in stunned myocardium. To examine the mechanism for reduced transporter activity, we followed the postischemic response of metabolite influx/efflux from mitochondria to stimulation of the malate-aspartate (MA) shuttle. Isolated rabbit hearts were either perfused with 2.5 mM [2-13C]acetate ( n = 7) or similarly reperfused ( n = 5) after 10-min ischemia. In other hearts, the MA shuttle was stimulated with a high cytosolic redox state (NADH) induced by 2.5 mM lactate in normal ( n = 6) or reperfused hearts ( n = 7). In normal hearts, the MA shuttle response accelerated transport from 8.3 ± 3.4 to 16.2 ± 5.0 μmol ⋅ min−1 ⋅ g dry wt−1. Although transport was reduced in stunned hearts, the MA shuttle was responsive to cytosolic NADH load, increasing transport from 3.4 ± 1.0 to 9.8 ± 3.7 μmol ⋅ min−1 ⋅ g dry wt−1. Therefore, metabolite exchange remains intact in stunned myocardium but responds to changes in TCA cycle flux regulation.

scholarly journals Association of the malate dehydrogenase-citrate synthase metabolon is modulated by intermediates of the Krebs tricarboxylic acid cycle

2021 ◽  
Author(s):  
Joy Omini ◽  
Izabela Wojciechowska ◽  
Aleksandra Skirycz ◽  
Hideaki Moriyama ◽  
Toshihiro Obata
Keyword(s):  
Malate Dehydrogenase ◽  
Metabolic Flux ◽  
Citrate Synthase ◽  
Tricarboxylic Acid Cycle ◽  
Feedback Regulation ◽  
Dynamic Structure ◽  
Tca Cycle ◽  
Tricarboxylic Acid ◽  
Enzyme Complex ◽  
Acetyl Coa

Mitochondrial malate dehydrogenase (MDH)-citrate synthase (CS) multi-enzyme complex is a part of the Krebs tricarboxylic acid (TCA) cycle 'metabolon' which is enzyme machinery catalyzing sequential reactions without diffusion of reaction intermediates into a bulk matrix. This complex is assumed to be a dynamic structure involved in the regulation of the cycle by enhancing metabolic flux. Microscale Thermophoresis analysis of the porcine heart MDH-CS complex revealed that substrates of the MDH and CS reactions, NAD+ and acetyl-CoA, enhance complex association while products of the reactions, NADH and citrate, weaken the affinity of the complex. Oxaloacetate enhanced the interaction only when it was presented together with acetyl-CoA. Structural modeling using published CS structures suggested that the binding of these substrates can stabilize the closed format of CS which favors the MDH-CS association. Two other TCA cycle intermediates, ATP, and low pH also enhanced the association of the complex. These results suggest that dynamic formation of the MDH-CS multi-enzyme complex is modulated by metabolic factors responding to respiratory metabolism, and it may function in the feedback regulation of the cycle and adjacent metabolic pathways.

scholarly journals Stimulation of beta-Carotene Synthesis in Blakeslea trispora by Pyruvate and Intermediates of the Tricarboxylic Acid (TCA) Cycle.

1969 ◽  
Vol 23 ◽  
pp. 2908-2909 ◽  
Author(s):  
Lars Björk ◽  
Halina Y. Neujahr ◽  
Baruch Yom-Tov ◽  
D. Heinegård ◽  
Alexandru T. Balaban ◽  
...  
Keyword(s):  
Beta Carotene ◽  
Tca Cycle ◽  
Tricarboxylic Acid ◽  
Blakeslea Trispora ◽  
Carotene Synthesis ◽  
Stimulation Of

scholarly journals Systems-Level Metabolic Flux Profiling Elucidates a Complete, Bifurcated Tricarboxylic Acid Cycle in Clostridium acetobutylicum

2010 ◽  
Vol 192 (17) ◽  
pp. 4452-4461 ◽  
Author(s):  
Daniel Amador-Noguez ◽  
Xiao-Jiang Feng ◽  
Jing Fan ◽  
Nathaniel Roquet ◽  
Herschel Rabitz ◽  
...  
Keyword(s):  
Metabolic Pathways ◽  
Genome Annotation ◽  
Clostridium Acetobutylicum ◽  
Metabolic Flux ◽  
Tricarboxylic Acid Cycle ◽  
Anaerobic Bacteria ◽  
Tca Cycle ◽  
Tricarboxylic Acid ◽  
Fermentation Products

ABSTRACT Obligatory anaerobic bacteria are major contributors to the overall metabolism of soil and the human gut. The metabolic pathways of these bacteria remain, however, poorly understood. Using isotope tracers, mass spectrometry, and quantitative flux modeling, here we directly map the metabolic pathways of Clostridium acetobutylicum, a soil bacterium whose major fermentation products include the biofuels butanol and hydrogen. While genome annotation suggests the absence of most tricarboxylic acid (TCA) cycle enzymes, our results demonstrate that this bacterium has a complete, albeit bifurcated, TCA cycle; oxaloacetate flows to succinate both through citrate/α-ketoglutarate and via malate/fumarate. Our investigations also yielded insights into the pathways utilized for glucose catabolism and amino acid biosynthesis and revealed that the organism's one-carbon metabolism is distinct from that of model microbes, involving reversible pyruvate decarboxylation and the use of pyruvate as the one-carbon donor for biosynthetic reactions. This study represents the first in vivo characterization of the TCA cycle and central metabolism of C. acetobutylicum. Our results establish a role for the full TCA cycle in an obligatory anaerobic organism and demonstrate the importance of complementing genome annotation with isotope tracer studies for determining the metabolic pathways of diverse microbes.

scholarly journals Distinct metabolic flux modes through the tricarboxylic acid cycle in mesophyll and guard cells revealed by GC-MS-based 13C-positional isotopomer analysis

2021 ◽  
Author(s):  
André G. Daubermann ◽  
Valéria F. Lima ◽  
Markus Schwarzländer ◽  
Alexander Erban ◽  
Joachim Kopka ◽  
...  
Keyword(s):  
Metabolic Flux ◽  
Tricarboxylic Acid Cycle ◽  
Tca Cycle ◽  
Positional Information ◽  
Guard Cells ◽  
Cell Types ◽  
Tricarboxylic Acid ◽  
Flux Analysis ◽  
List Type ◽  
Thioredoxin System

Summary13C-Metabolic flux analysis (13C-MFA) have greatly contributed to revealing the regulation of plant metabolism. However, mass spectrometry (MS) approaches have hitherto been limited in their power to deduce flux information due to lack of positional information.Here we established an MS-based 13C-positional isotopomer labelling approach and performed a multi-species/cell-types analysis based on previous 13C-MFA to compare flux modes through the tricarboxylic acid (TCA) cycle and associated pathways in mesophyll (MCs) and guard cells (GCs).Both cell types showed high 13C-enrichment in pyruvate. However, GCs and sink MCs, but not source MCs showed high 13C-incorporation into Glu/Gln following provision of 13C-sucrose. Only GCs showed higher 13C-enrichment in the carbon 1 atom of Gln, which is derived from PEPc-mediated CO2 fixation. Increased 13C-enrichment in the carbon 1 of Glu was also observed in both trxo1 and ntra ntrb mutants, but not in wild type Arabidopsis plants, following provision of 13C-glucose.Our results suggest that the mitochondrial thioredoxin system restricts the fluxes from PEPc and glycolysis to Glu in illuminated MCs and reveal that fluxes throughout the TCA cycle of GCs resemble those of sink MCs but operate different non-cyclic flux modes to support Gln synthesis in the light.

scholarly journals MCART1/SLC25A51 is required for mitochondrial NAD transport

2020 ◽  
Vol 6 (43) ◽  
pp. eabe5310 ◽  
Author(s):  
Nora Kory ◽  
Jelmi uit de Bos ◽  
Sanne van der Rijt ◽  
Nevena Jankovic ◽  
Miriam Güra ◽  
...  
Keyword(s):  
Nicotinamide Adenine Dinucleotide ◽  
Redox Reactions ◽  
Tca Cycle ◽  
Substrate Oxidation ◽  
Tricarboxylic Acid ◽  
Isolated Mitochondria ◽  
Mitochondrial Transporter ◽  
Transport Chain ◽  
Complex I Activity

The nicotinamide adenine dinucleotide (NAD+/NADH) pair is a cofactor in redox reactions and is particularly critical in mitochondria as it connects substrate oxidation by the tricarboxylic acid (TCA) cycle to adenosine triphosphate generation by the electron transport chain (ETC) and oxidative phosphorylation. While a mitochondrial NAD+ transporter has been identified in yeast, how NAD enters mitochondria in metazoans is unknown. Here, we mine gene essentiality data from human cell lines to identify MCART1 (SLC25A51) as coessential with ETC components. MCART1-null cells have large decreases in TCA cycle flux, mitochondrial respiration, ETC complex I activity, and mitochondrial levels of NAD+ and NADH. Isolated mitochondria from cells lacking or overexpressing MCART1 have greatly decreased or increased NAD uptake in vitro, respectively. Moreover, MCART1 and NDT1, a yeast mitochondrial NAD+ transporter, can functionally complement for each other. Thus, we propose that MCART1 is the long sought mitochondrial transporter for NAD in human cells.

scholarly journals TCA Cycle Defects and Cancer: When Metabolism Tunes Redox State

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
Simone Cardaci ◽  
Maria Rosa Ciriolo
Keyword(s):  
Redox State ◽  
Fumarate Hydratase ◽  
Tca Cycle ◽  
Tricarboxylic Acid ◽  
Cellular Redox ◽  
Redox Biology ◽  
Recessive Mutations ◽  
Tca Cycle Enzymes ◽  
The Tca Cycle ◽  
Inborn Defects

Inborn defects of the tricarboxylic acid (TCA) cycle enzymes have been known for more than twenty years. Until recently, only recessive mutations were described which, although resulted in severe multisystem syndromes, did not predispose to cancer onset. In the last ten years, a causal role in carcinogenesis has been documented for inherited and acquired alterations in three TCA cycle enzymes, succinate dehydrogenase (SDH), fumarate hydratase (FH), and isocitrate dehydrogenase (IDH), pointing towards metabolic alterations as the underlying hallmark of cancer. This paper summarizes the neoplastic alterations of the TCA cycle enzymes focusing on the generation of pseudohypoxic phenotype and the alteration of epigenetic homeostasis as the main tumor-promoting effects of the TCA cycle affecting defects. Moreover, we debate on the ability of these mutations to affect cellular redox state and to promote carcinogenesis by impacting on redox biology.

scholarly journals Association of the malate dehydrogenase-citrate synthase metabolon is modulated by intermediates of the Krebs tricarboxylic acid cycle

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Joy Omini ◽  
Izabela Wojciechowska ◽  
Aleksandra Skirycz ◽  
Hideaki Moriyama ◽  
Toshihiro Obata
Keyword(s):  
Malate Dehydrogenase ◽  
Metabolic Flux ◽  
Citrate Synthase ◽  
Tricarboxylic Acid Cycle ◽  
Feedback Regulation ◽  
Dynamic Structure ◽  
Tca Cycle ◽  
Tricarboxylic Acid ◽  
Enzyme Complex ◽  
Acetyl Coa

AbstractMitochondrial malate dehydrogenase (MDH)-citrate synthase (CS) multi-enzyme complex is a part of the Krebs tricarboxylic acid (TCA) cycle ‘metabolon’ which is enzyme machinery catalyzing sequential reactions without diffusion of reaction intermediates into a bulk matrix. This complex is assumed to be a dynamic structure involved in the regulation of the cycle by enhancing metabolic flux. Microscale Thermophoresis analysis of the porcine heart MDH-CS complex revealed that substrates of the MDH and CS reactions, NAD+ and acetyl-CoA, enhance complex association while products of the reactions, NADH and citrate, weaken the affinity of the complex. Oxaloacetate enhanced the interaction only when it was present together with acetyl-CoA. Structural modeling using published CS structures suggested that the binding of these substrates can stabilize the closed format of CS which favors the MDH-CS association. Two other TCA cycle intermediates, ATP, and low pH also enhanced the association of the complex. These results suggest that dynamic formation of the MDH-CS multi-enzyme complex is modulated by metabolic factors responding to respiratory metabolism, and it may function in the feedback regulation of the cycle and adjacent metabolic pathways.

scholarly journals The Metabolic Fates of Pyruvate in Normal and Neoplastic Cells

Cells ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 762
Author(s):  
Edward V. Prochownik ◽  
Huabo Wang
Keyword(s):  
Metabolic Pathways ◽  
Redox State ◽  
Pyruvate Dehydrogenase Complex ◽  
Tca Cycle ◽  
Vascular Supply ◽  
Extrinsic Factors ◽  
The Tca Cycle ◽  
Initial Substrate ◽  
Numerous Cell ◽  
Bio Synthesis

Pyruvate occupies a central metabolic node by virtue of its position at the crossroads of glycolysis and the tricarboxylic acid (TCA) cycle and its production and fate being governed by numerous cell-intrinsic and extrinsic factors. The former includes the cell’s type, redox state, ATP content, metabolic requirements and the activities of other metabolic pathways. The latter include the extracellular oxygen concentration, pH and nutrient levels, which are in turn governed by the vascular supply. Within this context, we discuss the six pathways that influence pyruvate content and utilization: 1. The lactate dehydrogenase pathway that either converts excess pyruvate to lactate or that regenerates pyruvate from lactate for use as a fuel or biosynthetic substrate; 2. The alanine pathway that generates alanine and other amino acids; 3. The pyruvate dehydrogenase complex pathway that provides acetyl-CoA, the TCA cycle’s initial substrate; 4. The pyruvate carboxylase reaction that anaplerotically supplies oxaloacetate; 5. The malic enzyme pathway that also links glycolysis and the TCA cycle and generates NADPH to support lipid bio-synthesis; and 6. The acetate bio-synthetic pathway that converts pyruvate directly to acetate. The review discusses the mechanisms controlling these pathways, how they cross-talk and how they cooperate and are regulated to maximize growth and achieve metabolic and energetic harmony.

scholarly journals Rapid and delayed effects of epidermal growth factor on gluconeogenesis

1993 ◽  
Vol 294 (3) ◽  
pp. 865-872 ◽  
Author(s):  
C Soler ◽  
M Soley
Keyword(s):  
Growth Factor ◽  
Epidermal Growth Factor ◽  
Redox State ◽  
Metabolic Flux ◽  
Isolated Hepatocytes ◽  
Delayed Effect ◽  
Delayed Effects ◽  
Mitochondrial Redox State ◽  
Glucose Synthesis ◽  
Epidermal Growth

Most reports on the effects of epidermal growth factor (EGF) on gluconeogenesis have indicated that such effects depend on the substrate used and are only observable after a lag time of 30-40 min. Recently, an immediate and transient effect of EGF on glucose synthesis was described in a perfused liver system. Here we extend the study of the effect of EGF on gluconeogenesis to isolated hepatocytes from fasted rats. The delayed effect of EGF on gluconeogenesis was studied by adding the substrate 40 min after the peptide. Under these conditions EGF increased glucose synthesis from pyruvate, decreased it when the substrate was lactate or glycerol and did not modify gluconeogensis from fructose or dihydroxyacetone. EGF did not affect the metabolic flux through glycolysis, determined as the production of lactate+pyruvate from 30 mM glucose. Furthermore, EGF did not modify the metabolic flux through pyruvate kinase, determined as the production of lactate+pyruvate from 1 mM dihydroxyacetone. The differing effects of EGF on gluconeogenesis depending on the substrate used can be explained by the effects of EGF on the cytosolic redox state (measured as the lactate/pyruvate ratio). About 20 min after the addition of EGF, the mitochondrial redox state (measured as the 3-hydroxybutyrate/acetoacetate ratio) decreased. This effect of EGF was blocked by ammonium, which also abolished the effect of the peptide on gluconeogenesis. Thus the effect of EGF at the mitochondrial level appears to be necessary for its effects on gluconeogenesis. Taken together, our results indicate that the delayed effects of EGF on gluconeogenesis are secondary to the effects of the peptide at both the mitochondrial and cytosolic levels. In addition to these delayed effects, we observed that EGF rapidly and transiently stimulated glucose synthesis from lactate, decreased the cytosolic redox state and increased oxygen consumption. All of these rapid effects required the presence of extracellular calcium and disappeared in the presence of rotenone, suggesting that this rapid effect of EGF on gluconeogenesis is secondary to the stimulation of mitochondrial respiration.

scholarly journals Biochemical elucidation of citrate accumulation in Synechocystis sp. PCC 6803 via kinetic analysis of aconitase

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Maki Nishii ◽  
Shoki Ito ◽  
Noriaki Katayama ◽  
Takashi Osanai
Keyword(s):  
Kinetic Analysis ◽  
Chemical Equilibrium ◽  
Isocitrate Dehydrogenase ◽  
Tca Cycle ◽  
Tricarboxylic Acid ◽  
Unicellular Cyanobacterium ◽  
Citrate Accumulation ◽  
Kinetics Of ◽  
Synechocystis Sp ◽  
Pcc 6803

AbstractA unicellular cyanobacterium Synechocystis sp. PCC 6803 possesses a unique tricarboxylic acid (TCA) cycle, wherein the intracellular citrate levels are approximately 1.5–10 times higher than the levels of other TCA cycle metabolite. Aconitase catalyses the reversible isomerisation of citrate and isocitrate. Herein, we biochemically analysed Synechocystis sp. PCC 6803 aconitase (SyAcnB), using citrate and isocitrate as the substrates. We observed that the activity of SyAcnB for citrate was highest at pH 7.7 and 45 °C and for isocitrate at pH 8.0 and 53 °C. The Km value of SyAcnB for citrate was higher than that for isocitrate under the same conditions. The Km value of SyAcnB for isocitrate was 3.6-fold higher than the reported Km values of isocitrate dehydrogenase for isocitrate. Therefore, we suggest that citrate accumulation depends on the enzyme kinetics of SyAcnB, and 2-oxoglutarate production depends on the chemical equilibrium in this cyanobacterium.

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