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Mammalian Cell Physiology
Published in Anthony S. Lubiniecki, Large-Scale Mammalian Cell Culture Technology, 2018
Lactate formation by some types of cells can be decreased by switching from glucose as a primary source of carbohydrate to other monosacharrides, such as fructose or galactose (53, 54, 62–65). The reason for this reduced lactate formation is presumably the slower transport and metabolism of fructose and galactose by cultured cells. This would reduce the amount of carbon entering the glycolytic pathway, reduce cellular pyruvate pools, and effectively reduce the amount of lactic acid formed. Since glycolysis is diminished in these cultures, they must adjust their metabolism to favor an aerobic production of ATP, presumably by using another oxidizable energy substrate such as glutamine. Reitzer et al. (66) found that HeLa cells were able to grow equally well on fructose, galactose, or glucose. They calculated that in the most extreme case, cells cultured on 2 mM fructose, the glycolytic activity of HeLa cells was reduced by approximately 900-fold. Their conclusion was that under these conditions almost all the fructose carbon passed through the pentose phosphate pathway for use as a biosynthetic precursor. In another paper, Reitzer et al. (67) suggested that the major function of the pentose phosphate pathway in HeLa cells was the generation of ribose-5-phosphate for nucleic acid synthesis. An earlier paper by Zielke et al. (68)showed the feasibility of growing normal human fibroblasts in the absence of glucose (for one or two cell divisions) when the medium was supplemented with hypoxanthine, thymidine, and uridine. Glutamine was the energy substrate used by HeLa cells (66, 67) and by normal human fibroblasts (68, 69) when their glycolytic rate was slowed. A discussion of the metabolism of glutamine and other amino acids will be covered in the next section of this chapter.
The Pentose Phosphates Pathway—Glucogenesis
Published in Jean-Louis Burgot, Thermodynamics in Bioenergetics, 2019
At this point, one considers that the oxidative phase of the pentose phosphates pathway is finished and that the nonoxidative one begins. In the non-oxidative phase, the isomerization ribulose-5-phosphate → ribose-5-phosphate occurs and the produced pentose phosphates in the oxidative phase are recycled in glucose-6-phosphate. The reaction ribulose-5-phosphate → ribose-5-phosphate evolves through an intermediary enediol as evolve the isomerizations glucose-6-phosphate → fructose-6-phosphate and dihydroyacetone phosphate → glyceraldehyde-3-phosphate.The isomerization ribulose-5-phosphate ribose-5-phosphate is done through the intermediary of the phosphopentose isomerase. The ribose-5-phosphate is a precursor for nucleotide synthesis. These isomerizations ketose-aldose evolve through an intermediary which is an enediol (Figure 103). Isomerization ribulose-5-phosphate → ribose-5-phosphate.Recycling pentose phosphates produced in the oxidative phase in glucose-6-phosphate are carried out by several steps.Firstly, there is epimerization of ribulose-5-phosphate in xylulose-5-phosphate: Epimerization ribulose-5-phosphate → xylulose-5-phosphate.
Proteomics investigation of molecular mechanisms affected by EnBase culture system in anti-VEGF fab fragment producing E. coli BL21 (DE3)
Published in Preparative Biochemistry and Biotechnology, 2019
Bahareh Azarian, Amin Azimi, Mahboubeh Sepehri, Vahideh Samimi Fam, Faegheh Rezaie, Yeganeh Talebkhan, Vahid Khalaj, Fatemeh Davami
Ribose 5-phosphate isomerase A (RPIA) is up-regulated in EnBase cultured cells at the end of the increased growth rate phase. RPIA catalyzes the reversible conversion of ribulose 5-phosphate to ribose 5-phosphate as a step of non-oxidative branch of pentose phosphate pathway (PPP). PPP is the major source for production of NADPH which serves as a reducing power in anabolic pathways of amino acid and lipid biosynthesis.[25] In addition to the production of NADPH, the intermediates of PPP are precursors to biosynthesis of amino acid, nucleic acid, and lipopolysaccharides.[26–28] Increased activity of PPP due to RPIA up-regulation in EnBase cultured cells provides a capacity for higher metabolic and biosynthetic activities.