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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).
Comparative proteomic analysis revealed the metabolic mechanism of excessive exopolysaccharide synthesis by Bacillus mucilaginosus under CaCO3 addition
Published in Preparative Biochemistry & Biotechnology, 2019
Hongyu Xu, Zhiwen Zhang, Hui Li, Yujie Yan, Jinsong Shi, Zhenghong Xu
Glucose-6-phosphate isomerase (Pgi), a second glycolytic enzyme, catalyzed the reversible aldose–ketose isomerization of glucose-6-phosphate to fructose 6-phosphate. This enzyme is also an enzymatic link between glycolysis and the pentose phosphate pathway.[27] 6-Phosphofructokinase (PfkA) was believed to be the most important element for the control of glycolytic flux. This enzyme catalyzes a physiologically reversible interconversion of fructose-6-phosphate and fructose-1,6-bisphosphate.[28] Aconitate hydratase (Acn), which transforms citrate to isocitrate, was the first step of the TCA cycle.[29] Glucose-6-phosphate dehydrogenase (G6PD) directed glucose-6-phosphate into the pentose phosphate pathway and played a pivotal role in cell function.[30] In this study, we found that all the four enzymes were down-regulated with CaCO3 addition and created a decreased carbon flux toward the growth of cells.