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31P
Published in Guillaume Madelin, X-Nuclei Magnetic Resonance Imaging, 2022
Tumor. Reprogrammation of the energy metabolism is one of the hallmarks of proliferating cancer cells [93]. It has been observed that even under aerobic conditions, cancer cells favor glycolysis to oxidative phosphorylation in the mitochondria to produce ATP, where only a little amount of pyruvate is dispatched to the oxygen-consuming mitochondria. This aerobic glycolysis phenomenon is usually called the Warburg effect [94]. It is an inefficient way to generate ATP in the cells, but it is thought to enable other pathways in cancer cells to acquire and metabolize nutrients to enable proliferation [95], as well as generating larger amounts of lactate which plays a key role in carcinogenesis [96]. 31P MRS could therefore prove to be a very useful tool to assess the energy metabolism in brain tumors in vivo.
Regulation of Osmolytes Syntheses and Improvement of Abiotic Stress Tolerance in Plants
Published in Hasanuzzaman Mirza, Nahar Kamrun, Fujita Masayuki, Oku Hirosuke, Tofazzal M. Islam, Approaches for Enhancing Abiotic Stress Tolerance in Plants, 2019
Ambuj Bhushan Jha, Pallavi Sharma
Higher accumulation of free amino acids, mainly branched-chain amino acids (BCAAs) such as isoleucine, leucine and valine, plays a key role in plant abiotic stress tolerance mechanisms (Planchet and Limami, 2015). Leucine, valine and isoleucine are of equal importance in plants, with the involvement of four common enzymes in their biosynthetic pathways (Joshi et al., 2010). Similarly, isoleucine, methionine and threonine pathways are interconnected in plants. Metabolism of threonine and methionine under changed developmental and environmental conditions affects the availability of isoleucine as those amino acids serve as a substrate for isoleucine biosynthesis (Joshi et al., 2010). Three different synthesis pathways, the glutamate family pathway, the pyruvate family pathway and the aspartate family pathway, operate in plants, and these pathways are under tight regulation during stressful conditions (Planchet et al., 2015). These pathways produce different amino acids that act as compatible osmolytes under adverse environmental conditions. The glutamate family pathway produces proline and γ-aminobutyric acid, whereas the pyruvate family pathway produces alanine, leucine and valine (Planchet and Limami, 2015). Further, the aspartate family pathway produces energy through lysine catabolism.
Applications in Biology
Published in Gabriel A. Wainer, Discrete-Event Modeling and Simulation, 2017
The Krebs cycle, also called the tri-carboxylic acid (TCA) cycle and the citric acid cycle (CAC), oxidizes pyruvate formed during the glycolysis pathway into CO2 and H2O. This cycle is a series of chemical reactions of central importance in all living cells that utilize oxygen. The citric acid cycle takes place within the mitochondria in eukaryotes and within the cytoplasm in prokaryotes. For each turn of the cycle, 12 ATP molecules are produced—one directly from the cycle and 11 from the oxidation of the three NADH and one FADH2 molecules produced by the cycle by oxidative phosphorylation [10]. Glucose is converted by glycolysis into pyruvate. Pyruvate enters the mitochondria, linking glycolysis to the Krebs cycle. This step (step A) is also called the bridging step. Pyruvate dehydrogenase—a complex of three enzymes and five coenzymes—oxidizes pyruvate using NAD+ to form acetyl CoA, NADH, and CO2.
Metabolomics profiling of valproic acid-induced symptoms resembling autism spectrum disorders using 1H NMR spectral analysis in rat model
Published in Journal of Toxicology and Environmental Health, Part A, 2022
Hyang Yeon Kim, Yong-Jae Lee, Sun Jae Kim, Jung Dae Lee, Suhkmann Kim, Mee Jung Ko, Ji-Woon Kim, Chan Young Shin, Kyu-Bong Kim
Mitochondrial dysfunction in ASD affects serum metabolites. Giulivi et al. (2010) reported that the activity of pyruvate dehydrogenase was lower in children with ASD compared to normal children, associated with rise in pyruvate and lactate levels. Because pyruvate dehydrogenase converts pyruvate to acetyl-CoA in the mitochondria, lower activity results in increased pyruvate and lactate levels. In the absence of oxygen, most cells continue glycolysis for a short duration to oxidize NADH through fermentation, which generates lactate from pyruvate. Generally, lactate travels to the liver through the bloodstream, where it is converted to glucose; and thus, blood glucose levels rise. It is of interest that Poling et al. (2006) found that plasma alanine levels were also elevated by mitochondrial electron transfer chain (ETC) dysfunction in ASD in agreement with our results. This may be attributed to an increase in activity of alanine transaminase, which converts pyruvate to alanine in ASD. In this study, lactate and glucose were significantly different, and these two serum metabolites might serve as biomarkers of VPA-induced ASD.
Biosynthesis of butyric acid by Clostridium tyrobutyricum
Published in Preparative Biochemistry and Biotechnology, 2018
Jin Huang, Wan Tang, Shengquan Zhu, Meini Du
Butyric acid has been produced from C. tyrobutyricum using various hexoses and pentoses, with acetic acid, CO2, and H2 formed as the major fermentation by-products.[2] The metabolic pathways of butyric acid production by C. tyrobutyricum with glucose and xylose have been revealed little by little (Figure 1). When glucose is used as the substrate, glucose (1 mol) is catabolized to pyruvate (2 mol) with ATP (2 mol) and NADH (2 mol) through Embden–Meyerhof–Pamas (EMP) pathway.[32] In the xylose pathway, the xylose substrate is catabolized to fructose 6-phosphate and glyceraldehyde-3-phosphate through the pentose phosphate pathway followed by phosphorylation, epimerization, then pyruvate formation under a series of enzymes; through that process, 5 mol pyruvate along with 5 mol ATP and 5 mol NADH is generated from 3 mol xylose.[28] In both pathways, pyruvate is then oxidized to acetyl-CoA with the release of CO2 and generated the reduced ferredoxin, which is reoxidized by hydrogenase as electron transfer to hydrogen ions to form H2. Under certain conditions, pyruvate may also be converted to lactate by lactate dehydrogenase (LDH) . Acetyl-CoA is converted either to acetate by PTA and AK or to acetoacetyl-CoA under the catalysis of thiolase, which is followed by conversion to butyryl-CoA through a series of enzymes (β-hydroxybutyryl-CoA dehydrogenase, crotonase, and butyryl CoA dehydrogenase). Butyryl-CoA, which is the key precursor in the formation of butyric acid, is further converted to butyryl-P by PTB and finally to butyric acid by BK.[323334] Glucose and xylose fermentation by C. tyrobutyricum follow the stoichiometric equations below: