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Mammalian Cell Physiology
Published in Anthony S. Lubiniecki, Large-Scale Mammalian Cell Culture Technology, 2018
The activities of key enzymes in the pentose phosphate pathway were also found to be elevated in tumor as compared to normal liver tissue but were generally not linked to growth rate. However, the activity of phosphoribosylpyrophosphate (PRPP) synthetase was found to be positively correlated with the tumor growth rate. PRPP can be used in both salvage and de novo pathways of purine and pyrimidine biosynthesis, functioning as an allosteric activator of the rate-limiting enzyme of de novo pyrimidine biosynthesis. Activation of these enzymes would therefore greatly favor DNA replication and growth. Activities of enzymes involved in pentose phosphate synthesis and utilization are compared in transformed and normal tissues from both liver and kidney in Table 3. Weber (84, 85) concluded that an imbalance in the carbohydrate metabolism of cancer cells is the result of reprogramming of gene expression. He suggests that the expression of key enzymes will alter the phenotype of cancer cells, giving them a growth advantage over normal tissue.
Outdoor Air Pollution
Published in William J. Rea, Kalpana D. Patel, Reversibility of Chronic Disease and Hypersensitivity, Volume 4, 2017
William J. Rea, Kalpana D. Patel
Cycling cells have higher NADPH/NADP+ ratios than postmitotic cells.242 Cultured cells must double their biomass each day in preparation for division. Postmitotic cells in tissues do not increase in their biomass. Postmitotic cells direct electrons to NADH for cellular work, not NADPH for biomass production. This essential difference between growing and nongrowing cells must be grasped before the different roles of mitochondria in growing and nongrowing cells can be understood. The synthesis of lipids, proteins, DNA, and RNA requires the use of electrons carried by NADPH to make new carbon–carbon and other chemical bonds. NADPH is made in large amounts by the pentose phosphate pathway in which glucose 6-phosphate is used before entering glycolysis to make ribose for DNA and RNA synthesis and NADPH for macromolecular synthesis and glutathione metabolism.243 When incoming electrons from glucose and other nutrients are directed to NADPH, those electrons are not available for NADH used in mitochondrial oxidative phosphorylation. The combined effect of increased NADPH and hyperoxia (21% O2) in cell culture conspires to amplify superoxide and hydrogen peroxide production by NADPH oxidases, making the study of more subtle factors such as regulation of the pentose phosphate pathway by nitric oxide244 and compartmental redox regulation during differentiation challenging or impossible.
Production of Butanol from Corn
Published in Shelley Minteer, Alcoholic Fuels, 2016
Thaddeus C. Ezeji, Nasib Qureshi, Patrick Karcher, Hans P. Blaschek
The uptake of carbohydrates in the solventogenic clostridia is achieved by a phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS). This mechanism involves simultaneous uptake and phosphorylation of substrate that results in the conversion of glucose to glucose-6-phosphate, which is subsequently metabolized to pyruvate via the Embden-Meyerhof-Parnas (EMP) pathway (Mitchell, 2001). Fructose is converted to fructose-1-phosphate and enters the EMP pathway upon conversion to fructose 1,6-bisphosphate. D-xylose is converted to D-xylulose by the xylose isomerase enzyme and the metabolism proceeds by a phosphorylation reaction. The reaction is catalyzed by xylulokinase, which results in the formation of D-xylulose-5-phosphate. The pentose phosphate pathway utilizes enzymes transaldolase and transketolase to convert D-xylulose-5-phosphate to glyceraldehyde-3-phosphate and fructose-6-phosphate (Singh and Mishra, 1995). The glyceraldehyde-3-phosphate and fructose-6-phosphate enter the EMP pathway leading to the formation of pyruvate. The ability of solventogenic clostridia to metabolize these sugars is important when corn is considered as the starting material for fermentation, as all of these sugars can be derived from corn or corn coproducts.
The effect of NADPH oxidase inhibitor diphenyleneiodonium (DPI) and glutathione (GSH) on Isatis cappadocica, under Arsenic (As) toxicity
Published in International Journal of Phytoremediation, 2021
Zahra Souri, Naser Karimi, Parvaiz Ahmad
Inhibition of NADPH oxidases decreases the activities of GSH dependent enzymes such as GR and GST. The oxidative pentose phosphate pathway influences GSH metabolism (Kong et al.1999; de Freitas-Silva et al.2017) where in glucose-6-phosphate dehydrogenase (G6PDH) provides the NADPH required for the production of GSH and GR activation (Kong et al.1999; de Freitas-Silva et al.2017; Souri et al.2018). Therefore, DPI had a negative effect GR activity and GST that may be due to inhibition of NADPH oxidases and finally reduce the generation of NADP+. On the other side, GR activity, which catalyzes the NADPH-dependent reduction of oxidized GSH enhanced markedly at As + GSH treatment that imply the positive role of GSH.
Enhancement of erythritol production by Trichosporonoides oedocephalis ATCC 16958 through regulating key enzyme activity and the NADPH/NADP ratio with metal ion supplementation
Published in Preparative Biochemistry and Biotechnology, 2018
Liangzhi Li, Pei Kang, Xin Ju, Jiajia Chen, Huibin Zou, Cuiying Hu, Lishi Yan
Finally, the pentose phosphate pathway is a major way to produce NADPH for reductive biosynthesis reactions.[32] In general, NADPH/NADP ratio >1.0, glucose-6-phosphate dehydrogenase (G6PD), and 6-Phosphogluconate dehydrogenase (6PGD) are responsible for most of NADPH production in the cytosol.[33] Specifically, NAD(P)H is essential for erythritol and glycerol synthesis as a cofactor.[5] Since T. oedocephalis consumes NADPH during the catalytic conversion of glucose to erythritol and redox potential is largely dependent on the balance between NADPH/NADP and NAD/NADH in cells, we further measured the intracellular ratio of NADPH/NADP. As shown in Figure 4, the NADPH/NADP ratio was slightly lower in T. oedocephalis cells cultured with Cu2+ in fermentation medium, compared with that of control cells. Therefore, total production of polyols (data not shown), which includes erythritol and glycerol, was lower after copper ion supplementation compared with the control value. Interestingly, the NADPH/NADP ratio always exceeded 1.9 in the present study, suggesting that the reduced forms were dominant during the whole fermentation period. At 108 hr of culture, the NADPH/NADP ratio peaked and highest reduction power was obtained, mainly because glucose was almost completely consumed (Figure 3), and optimal NADPH amounts are needed for polyol synthesis. At the end of fermentation when the carbon source is exhausted, erythritol and glycerol are gradually consumed again. Figure 3 also presented the typical profiles of polyol production.