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Assessment of Myocardial Metabolism with Magnetic Resonance Spectroscopy
Published in Robert J. Gropler, David K. Glover, Albert J. Sinusas, Heinrich Taegtmeyer, Cardiovascular Molecular Imaging, 2007
In addition, the ratio of the steady-state enrichment of either C2 or C3 labeled glutamate to C4-labeled glutamate is routinely used as an index of anaplerosis. Anaplerosis is defined as entry into citric acid cycle at a site other than acetyl-CoA. Since the pool sizes for the citric acid cycle intermediates remain relatively constant, there must be a balance between anaplerosis and exit from the citric acid cycle at a site other than the decarboxylation steps at citrate → α-ketoglutarate and succinyl-CoA → fumarate. While we know in the isolated rat or rabbit heart that increasing the diversity of substrates increases the amount of anaplerosis (from ~10% with glucose only, to ~20% with glucose, palmitate, and β-hydroxy-butyrate), little is known about the routes of substrate exit from the citric acid cycle. Reduced anaplerosis may lead to reduced citric acid flux and contribute the cardiac manifestations of diseases where fatty acid is used as the predominant energy fuel such as obesity and diabetes mellitus. Conversely, increased anaplerosis may contribute to increased ATP production and cardioprotection during ischemia (41).
Coupling Biogas with PHA Biosynthesis
Published in Martin Koller, The Handbook of Polyhydroxyalkanoates, 2020
Yadira Rodríguez, Victor Pérez, Juan Carlos López, Sergio Bordel, Paulo Igor Firmino, Raquel Lebrero, Raúl Muñoz
Another factor to be considered to design efficient production processes, which involve cycles of nitrogen feeding and starvation, is the fact that PHB is used by the cells as a storage compound that can be used as an energy or carbon source for growth when nitrogen sources become available. The consumption of PHB in methanotrophs has been studied in Methylocystis parvus [54] (Figure 14.2), which revealed that when nitrogen supply is restored, PHB-containing cells use the biopolymer as a carbon and energy source for protein synthesis (evidenced by their increased protein content), but cells do not divide. However, when methane is available following N supply restoration, methanotrophic cells start dividing at a faster rate (compared with those without stored PHB), and methane and PHB are consumed simultaneously. Metabolic modeling shows that during this co-consumption, methane is used as an energy source, while PHB is used as a carbon source. This is because when methane is assimilated through the serine cycle (a mechanism common to all type II methanotrophs, including Methylocystis), it is transformed into acetyl-CoA, which itself is fed to the TCA cycle leading to the production of NADH and the subsequent production of ATP in the respiratory chain. For cells to grow, metabolic precursors must also be supplied for the synthesis of amino acids and other biomass building blocks. If metabolic precursors are to be drained from the serine or the TCA cycle, other reactions have to produce intermediates of these cycles to replenish the precursors drained for biosynthesis. These are called anaplerotic reactions and are essential for aerobic cell growth. In organisms that rely on glycolysis, the most common anaplerotic reaction is pyruvate carboxylase. For methanotrophs using the serine cycle, the hypothesis is that the anaplerotic function is played by glycine synthase [52], which produces glycine from methylene tetrahydrofolate and drains serine, from where the rest of biomass building blocks are synthesized. Simulations of methane and PHB co-consumption [53] revealed that in this scenario, PHB is degraded via crotonyl-CoA to glyoxylate and succinyl-CoA. Glyoxylate replenishes the serine cycle, and succinyl-CoA replenishes the TCA cycle, which allows cells to withdraw both serine and α-ketoglutarate for biosynthesis, leading to the observed decrease in duplication time for PHB-containing cells. Schematic representation of methane and PHB co-consumption when both nitrogen and methane are supplied to PHB accumulating cells of M. parvus.
Amino Acids and Vitamin Production
Published in Debabrata Das, Soumya Pandit, Industrial Biotechnology, 2021
The aims for increase in production of l-lysine include price reduction. Glucose is phosphorylated upon cellular absorption in which it gets converted to glucose-6-phosphate and there is a consumption of phosphoenolpyruvate. However, it is observed that sucrose gets converted to fructose and also glucose-6-phosphate under the process of phosphotransferase system and also the invertase reaction. The Embden–Meyerhof–Parnas process undergoes the catalysis of glucose which is also known as glycolysis and the pentose phosphate pathway. Glucose-6-phosphate isomerase and glucose-6- phosphate dehydrogenase compete for the substrate glucose-6-phosphateduring the glucose catabolism, which results in either fructose-6phosphate or 6-phosphogluconolactone, respectively. It is seen that for the pentose phosphate cycle the oxidative part is the reason where glucose-6-phosphate gets converted into ribulose-5-phosphate under the supply of reduction equivalents in the form of NADPH. There is also an interconversion seen between pentose, hexose, and triode phosphates while proceeding the pentose phosphate cycle. 5-phosphoribosyl-l-pyrophosphate is necessary through nucleoside biosynthesis and acts as a precursor in nucleoside biosynthesis for the production of aromatic amino acids. The NADPH functions like a reduction equivalent in the numerous anabolic biosynthesis. Its assumption is that 4 NADPH molecules are used in the biosynthesis of one lysine molecule. Therefore the carbon flux remains constant. Some enzymes are identified as anaplerotic enzymes, including pyruvate carboxykinase, pyruvate carboxylase and also phosphoenol pyruvate carboxylase, phosphoenol pyruvate carboxylase or also known as PEPC. These enzymes catalyse the reaction by the addition of one mole of CO2 to the phosphoenol pyruvate and pyruvate. This fulfils the TCA and OAA. This also plays a role in supplying aspartic acid and the subsequent formation of lysine and others. With L-aspartate inflow into the lysine pathway, which is synthesized by oxaloacetate transamination by C. glutamicum, this will transform 2,6-dicarboxylate to diaminopimelate to l-lysine intermediate piperdine. There are two different routes to achieve this. There are two points where the carbon flux is regulated. At the first point feedback inhibition of aspartate kinase is observed by monitoring the levels of both L-threonine and L-lysine. At the second point, the level of dihydrodipicolinate synthase is controlled. L-lysine export has also been shown to be an important factor for l-lysine production. Fermentation of L-Lysine is also regulated by type of carbon-source, nitrogen-source, presence of metal ion concentration, dissolve oxygen concentration, temperature, and pH of the microbial medium (Bender, 2012).
Energy budget in Alona guttata (Chydoridae: Aloninae) and toxicant-induced alterations
Published in Journal of Environmental Science and Health, Part A, 2019
Olga C. Osorio-Treviño, Mario A. Arzate-Cárdenas, Roberto Rico-Martínez
Alona guttata exhibited a higher sensitivity for protein depletion in proportions of 0.05 LC50 to 0.20 LC50 for DM, and 0.1 to 0.2 LC50 for Pb2+, although at the highest concentrations tested, the energy budget was affected in all its components at similar depletion rates, which denotes a high demand for energy to deal with the effect of toxic exposure. High protein consumption has been related to proteolysis and the release of free amino acids that, after the transamination, could be incorporated into the tricarboxylic acid cycle (anaplerotic metabolic pathway) to acquire reducing power and finally the energy required for maintenance and detoxification.[30] This effect is commonly observed in daphnids[31,32] but it seems that the damage produced in Alona's tissues was extensive, and it compromised fertility and survival.