Role of tricarboxylic acid cycle in mechanisms of chemoreception

1961 ◽  
Vol 51 (1) ◽  
pp. 1-5
Author(s):  
T�ng Hsi-hsien
Keyword(s):  
Tricarboxylic Acid Cycle ◽  
Tricarboxylic Acid ◽  
Acid Cycle

Sporulation ofGibberella ZeaeIV. Role of the Tricarboxylic-Acid Cycle in Macroconidium Production

Mycologia ◽  
1979 ◽  
Vol 71 (4) ◽  
pp. 688-698 ◽  
Author(s):  
Bor-Fuei Huang ◽  
R. F. Dawson ◽  
R. A. Cappellini
Keyword(s):  
Tricarboxylic Acid Cycle ◽  
Tricarboxylic Acid ◽  
Acid Cycle

scholarly journals Role of Phosphoenolpyruvate in the NADP-Isocitrate Dehydrogenase and Isocitrate Lyase Reaction in Escherichia coli

2006 ◽  
Vol 189 (3) ◽  
pp. 1176-1178 ◽  
Author(s):  
Tadashi Ogawa ◽  
Keiko Murakami ◽  
Hirotada Mori ◽  
Nobuyoshi Ishii ◽  
Masaru Tomita ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Isocitrate Dehydrogenase ◽  
Isocitrate Lyase ◽  
Tricarboxylic Acid Cycle ◽  
Tricarboxylic Acid ◽  
Glyoxylate Shunt ◽  
Acid Cycle ◽  
Uncompetitive Inhibition

ABSTRACT Phosphoenolpyruvate inhibited Escherichia coli NADP-isocitrate dehydrogenase allosterically (Ki of 0.31 mM) and isocitrate lyase uncompetitively (Ki ′ of 0.893 mM). Phosphoenolpyruvate enhances the uncompetitive inhibition of isocitrate lyase by increasing isocitrate, which protects isocitrate dehydrogenase from the inhibition, and contributes to the control through the tricarboxylic acid cycle and glyoxylate shunt.

THE ROLE OF ASPARTIC ACID IN THE BIOSYNTHESIS OF RICININE1

1966 ◽  
Vol 44 (1) ◽  
pp. 23-27 ◽  
Author(s):  
S. R. Johns ◽  
Léo Marion
Keyword(s):  
Aspartic Acid ◽  
Tricarboxylic Acid Cycle ◽  
Tricarboxylic Acid ◽  
Acid Cycle ◽  
Ring Nitrogen

Ricinine, isolated from Ricinuscommunis L. fed aspartic acid-3-14C and aspartic acid-4-14C, was degraded, and in each case the activity of all the carbon atoms was determined. The results obtained indicate that aspartic acid is incorporated into ricinine via the Krebs tricarboxylic acid cycle rather than directly as aspartic acid. Experiments with aspartic acid-13N support this suggestion; they indicate that the ring nitrogen from ricinine is not derived directly from the nitrogen of aspartic acid, since both it and the nitrile nitrogen contain essentially the same abundance of 15N.

Studies on wheat plants using 14C-labelled compounds. XXII. Incorporation into wheat protein

1969 ◽  
Vol 47 (1) ◽  
pp. 19-23 ◽  
Author(s):  
W. B. McConnell
Keyword(s):  
Glutamic Acid ◽  
Specific Activity ◽  
Tricarboxylic Acid Cycle ◽  
Tricarboxylic Acid ◽  
Radioactive Tracers ◽  
Wheat Protein ◽  
Acid Cycle ◽  
Late Stages ◽  
Kernel Protein

Thatcher wheat plants were labelled with 14C by injecting radioactive tracers into the top internode of the stem during late stages of plant growth. The distribution of 14C in fully mature plants was examined, emphasis being placed on the labelling of kernel-protein amino acids.Glutamine was only slightly more effective than glutamic acid for labelling glutamic acid isolated from the gluten hydrolysate, indicating that glutamic acid and glutamine are extensively interconverted in the wheat plants. Proline and glutamic acid also are readily interconverted, proline-14C yielding protein in which the glutamic acid has a higher specific activity than does the proline. By contrast, arginine-5-14C did not yield highly labelled glutamic acid.14C from glyoxylate-1-14C was widely distributed among kernel components but it produced glycine and serine with carboxyl carbons of exceptionally high specific activity.Succinate-1,4-14C, succinate-2,3-14C, and aspartic acid-14C all labelled glutamic acid of kernel protein more extensively than the other amino acids of the protein. The role of the tricarboxylic acid cycle in utilizing these tracers is discussed.

scholarly journals New Insights into Heme Utilization Pathways

Blood ◽  
2019 ◽  
Vol 134 (Supplement_1) ◽  
pp. SCI-25-SCI-25
Author(s):  
Emanuela Tolosano
Keyword(s):  
Respiratory Chain ◽  
Tricarboxylic Acid Cycle ◽  
Tca Cycle ◽  
Tricarboxylic Acid ◽  
Energetic Metabolism ◽  
Acid Cycle ◽  
Heme Synthesis ◽  
Chain Complexes ◽  
The Tca Cycle

Heme, an iron-containing porphyrin, plays pivotal functions in cell energetic metabolism, serving as a cofactor for most of the respiratory chain complexes and interacting with the translocases responsible for the ADP/ATP exchange between mitochondria and cytosol. Moreover, heme biosynthesis is considered a cataplerotic pathway for the tricarboxylic acid cycle (TCA) cycle, as the process consumes succynil-CoA, an intermediate of the TCA cycle. Finally, heme synthesis is one of the major cellular iron-consuming processes, thus competing with mitochondrial biogenesis of iron-sulfur (Fe-S) clusters, the crucial cofactors of electron transport chain complexes and of some TCA cycle enzymes. The process of heme synthesis consists of eight enzymatic reactions starting in mitochondria with the condensation of glycine and succynil-CoA to form δ-aminolevulinic acid (ALA), catalyzed by amino levulinic acid synthase (ALAS), the rate-limiting enzyme in heme biosynthetic pathway. Two isoforms of ALAS exist, ALAS1, ubiquitously expressed and controlled by heme itself through a negative feedback, and ALAS2, specifically expressed in the erythroid cells and mainly controlled by iron availability. ALA is exported from mitochondria to cytosol and converted to coproporphyrinogenIII that is imported back into the mitochondrial intermembrane space and converted to protoporphyrinogen IX. The latter is oxidized to porphyrin IX. Finally, ferrous iron is inserted into porphyrin IX by ferrochelatase, a Fe-S cluster-containing enzyme. Heme is incorporated into mitochondrial heme-containing proteins including complexes of the respiratory chain or exported to cytosol for incorporation into cytosolic apo-hemoproteins. Cytosolic heme level is maintained by the rate of hemoprotein production, the activity of heme transporters, including both heme importers and exporters, and the rate of heme degradation mediated by heme oxygenases. The concerted action of all these mechanisms regulates heme level that in turn controls its own synthesis by regulating the expression and activity of ALAS1. During differentiation of erythroid progenitors, cells bypass the heme-mediated negative regulation of its production by expressing ALAS2 that is responsible for the high rate of heme synthesis required to sustain hemoglobin production. We showed that the process of heme efflux through the plasma membrane heme exporter Feline Leukemia Virus C Receptor (FLVCR)1a is required to sustain ALAS1-catalyzed heme synthesis. In tumor cells, the potentiation of heme synthesis/export axis contributes to the down-modulation of tricarboxylic acid cycle (TCA) cycle favoring a glycolysis- compared to an oxidative-based metabolism. Our data indicate that the heme synthesis/export axis slow down the TCA cycle through two mechanisms, on one hand, by consuming succynil-CoA, an intermediate of the cycle, and, on the other, by consuming mitochondrial iron thus limiting the production of Fe-S clusters, essential co-factors of complexes of the respiratory chain as well as of key enzymes of the cycle. The importance of heme synthesis/export axis in metabolic rewiring occurring during tumorigenesis is highlighted by the impaired proliferation and survival observed in FLVCR1a-silenced cancer cells. We speculate that the heme synthesis/export axis plays a role in metabolic adaptation also in proliferating cells in physiologic conditions, especially when oxygen concentration is limiting, as suggested by the phenotype of murine models of Flvcr1a deficiency. Finally, in post-mitotic cells the heme synthesis/export axis might contribute to modulate mitochondrial activity. This conclusion is supported by the observation that FLVCR1 gene was found mutated in human pathologies characterized by impaired function of neuronal cell populations strongly dependent on mitochondrial oxidative metabolism. In conclusion, our data highlight the crucial role of heme synthesis/export axis in the control of cell energetic metabolism. Future work is required to elucidate the role of exported heme in the extracellular environment. Disclosures No relevant conflicts of interest to declare.

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