Pentose-phosphate shunt

Figure 7.1 Scheme for integration of pentose phosphate shunt and glycolysis. 

Plant metabolism can be separated into primary pathways that are found in all cells and deal with manipulating a uniform group of basic compounds, and secondary pathways that occur in specialized cells and produce a wide variety of unique compounds. The primary pathways deal with the metabolism of carbohydrates, lipids, proteins, and nucleic acids and act through the many-step reactions of glycolysis, the tricarboxylic acid cycle, the pentose phosphate shunt, and lipid, protein, and nucleic acid biosynthesis. In contrast, the secondary metabolites (e.g., terpenes, alkaloids, phenylpropanoids, lignin, flavonoids, coumarins, and related compounds) are produced by the shikimic, malonic, and mevalonic acid pathways, and the methylerythritol phosphate pathway (Fig. 3.1). This chapter concentrates on the synthesis and metabolism of phenolic compounds and on how the activities of these pathways and the compounds produced affect product quality. 

Under basal conditions 5% of brain glucose is metabolized via the pentose phosphate shunt (PPS), also termed the hexose monophosphate pathway [66], a pathway active in both neurons and astrocytes. The PPS has... 

OCD obsessive—compulsive disorder PPS pentose phosphate shunt... 

The conclusion that the significance of the pentose phosphate shunt may be in keeping NADP in its reduced state and furnishing pentose phosphates for biosynthesis, rather than G-6-P utilization, is closely confirmed by the fact that individuals deficient in or lacking G-6-PDH activity suffer from a number of metabolic disorders due to lack of NADPH2 generation and nucleotide depletion. 

The NADPH level is clearly important for phase 1 reactions, yet many biochemical processes, such as fatty acid biosynthesis, use this coenzyme. It is derived from either the pentose phosphate shunt or isocitrate dehydrogenase. Consequently, the overall metabolic... 

Figure 6.18 The various protective roles of reduced GSH and the relationship with GSSG. The NAD PH may be regenerated by the pentose phosphate shunt. Abbreviations GSH, glutathione GSSG, oxidized glutathione.

Kudryavtseva, G.V. (1990). Ecologio-physiological features and the role of the pentose-phosphate shunt for carbohydrate metabolism in adaptations of lower aquatic vertebrates (Cyclostomes and Pisces) (In Russian). Uspekhi Sovremennoy Biologii 109,171-182. 

Saha, N Stoll, B., Lang, F., Haussinger, D. (1992). Effect of anisotonic cell volume modulation on glutathione-S-conjugate release, t-butylhydroperoxide metabolism and the pentose-phosphate shunt in perfused rat liver. Eur. J. Biochem. 209, 437-444. 

Fig. 8.2 Glycolysis and related pathways. Glycolysis is a central metabolic machinery in which one mole of glucose is catabolized to two moles of pyruvate, NADH, and ATP. Under aerobic conditions, pyruvate is further oxidized by mitochondrial system. In erythrocytes DHAP is a dead-end product however, in brain it can be converted into direction of lipid synthesis. Glycolysis and the pentose phosphate pathway (pentosePP) are interconnected via fructose-6-P and glyceral-dehyde-3-P. A high level of NADPH favors lipid synthesis via pentose phosphate shunt (pentosePP). At TPI inhibition (TPI deficiency), glyceraldehyde-3-Pcan be produced via G6PDH as well, to contribute to the glycolytic flux. a-GDH catalyzes the...

The rest of the Calvin cycle is involved in interconversion of carbohydrates to make glucose (or starch) and the regeneration of the ribulose-bisphosphate acceptor. The reactions are also found in the pathways for gluconeogenesis and the pentose phosphate shunt (see Volume 1, Chapters 10 and 12). The first step is the phosphorylation of 3-phosphoglycerate by the same reactions involved in gluconeogenesis. 

Cytoplasm Cytoplasm is a jelly-like substance that is sometimes described as "the cell-matrix". It holds the organelles in place within the cell. Site for Glycolysis and most of gluconeogenesis Pentose Phosphate shunt Fatty acid biosynthesis. 

Fig. 18. Effect of glucose on insulin release, glucose oxidation, pentose phosphate shunt, NADH/NAD +, NADPH/NADP"1", GSH/GSSG ratios and Ca + uptake of rat pancreatic islets. In a concentration range up to 16.7 mM, glucose-mediated stimulation of insulin secretion is closely parallelled by increases in glucose oxidation, pentose phosphate shunt activity, the NADH/NAD+, NADPH/NADP+, GSH/GSSG ratios and Ca2+ uptake (Ammon and Wahl, 1994).

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