Pentose phosphate pathway and

Glycolysis, the pentose phosphate pathway, and fatty acid synthesis are all found in the cytosol. In gluconeo-genesis, substrates such as lactate and pyruvate, which are formed in the cytosol, enter the mitochondrion to yield oxaloacetate before formation of glucose. 

Pathways are compartmentalized within the cell. Glycolysis, glycogenesis, glycogenolysis, the pentose phosphate pathway, and fipogenesis occur in the cytosol. The mitochondrion contains the enzymes of the citric acid cycle, P-oxidation of fatty acids, and of oxidative phosphorylation. The endoplasmic reticulum also contains the enzymes for many other processes, including protein synthesis, glycerofipid formation, and dmg metabolism. 

Figure 20-h Flow chart of pentose phosphate pathway and its connections with the pathway of glycolysis. The full pathway, as indicated, consists of three interconnected cycles in which glucose 6-phosphate is both substrate and end product. The reactions above the broken line are nonreversible, whereas all reactions under that line are freely reversible apart from that catalyzed by fructose-1,6-bisphosphatase. 

Nevertheless, using GC-based technologies, the quantification of several important intermediates of central metabolism, especially phosphorylated intermediates, is not very reliable, presumably because these compounds and their derivatives are not thermostable. For an analysis of these groups of metabolites, an LC-MS (liquid chromatography or HPLC coupled to MS) is more suitable, because it eliminates the need for volatility and thermostability and thereby eliminates the need for derivatization. Using a triple quadrupole MS, most of the intermediates in glycolysis, in the pentose phosphate pathway, and in the tricarboxylic acid cycle were measured in E. coli [214]. 

B. Luo, K. Groenke, R. Takors, C. Wandrey, and M. Oldiges, Simultaneous determination of multiple intracellular metabolites in glycolysis, pentose phosphate pathway and tricarboxylic acid cycle by liquid chromatography mass spectrometry. J. Chromatogr. A 1147, 153 164 (2007). 

Figure 5.12 Links between glycolysis, pentose phosphate pathway and Rapoport shuttle...

Sabri Ml. 1984. In vitro effect of n-hexane and its metabolites on selected enzymes in glycolysis, pentose phosphate pathway and citric acid cycle. Brain Res 297 145-150. 

Fig. 2. Experimental design of a C tracer experiment for the determination of the flux partitioning ratio between pentose phosphate pathway and glycolysis ( ppp) C label distribution from l- C glucose through the network with C atoms (black) and C atoms (white)...

Fig. 5. Estimation of the flux partitioning ratio between pentose phosphate pathway and glycolysis (4>ppp) from the lysine intensity ratio Im+i/m =1-11 using the optimization function fmincon implemented in Matlab. The numbered data points indicate the results obtained through the different iterations. Starting from ppp = 0.1, the optimal fit of experimental and calculated labeling was obtained after 14 iterations...

In this chapter we describe the individual reactions of glycolysis, gluconeogenesis, and the pentose phosphate pathway and the functional significance of each pathway. We also describe the various fates of the pyruvate produced by glycolysis they include the fermentations that are used by many organisms in anaerobic niches to produce ATP and that are exploited industrially as sources of ethanol, lactic acid, and other... 

An interesting and provocative analysis of the interplay between the pentose phosphate pathway and glycolysis, from a theoretical standpoint. 

Summary of Chapter 13 Pentose Phosphate Pathway and NADPH... 

Chapter 12 Metabolism of Monosaccharides and Disaccharides 135 Chapter 13 Pentose Phosphate Pathway and NADPH 143 Chapter 14 Glycosaminoglycans and Glycoproteins 155... 

An example of an a-ketol formation that does not involve decarboxylation is provided by the reaction catalyzed by transketolase, an enzyme that plays an essential role in the pentose phosphate pathway and in photosynthesis (equation 21) (B-77MI11001). The mechanism of the reaction of equation (21) is similar to that of acetolactate synthesis (equation 20). The addition of (39) to the carbonyl group of (44) is followed by aldol cleavage to give a TPP-stabilized carbanion (analogous to (41)). The condensation of this carbanionic intermediate with the second substrate, followed by the elimination of (39), accounts for the observed products (B-7IMIHOO1). 

The six-carbon chain of ManNAc 6-P can be extended by three carbon atoms using an aldol-type condensation with a three-carbon fragment from PEP (Eq. 20-7, step c) to give N-acetylneuraminic acid (sialic acid).48 Tire nine-carbon chain of this molecule can cyclize to form a pair of anomers with 6-membered rings as shown in Eq. 20-7. In a similar manner, arabi-nose 5-P is converted to the 8-carbon 3-deoxy-D-manno-octulosonic acid (KDO) (Fig. 4-15), a component of the lipopolysaccharide of gram-negative bacteria (Fig. 8-30), and D-Erythrose 4-P is converted to 3-deoxy-D-arafrmo-heptulosonate 7-P, the first metabolite in the shikimate pathway of aromatic synthesis (Fig. 25-1).48a The arabinose-P used for KDO synthesis is formed by isomerization of D-ribulose 5-P from the pentose phosphate pathway, and erythrose 4-P arises from the same pathway. 

If at any time only a little ribose 5-phosphate is required for nucleic acid synthesis and other synthetic reactions, it will tend to accumulate and is then converted to fructose 6-phosphate and glyceraldehyde 3-phosphate by the enzymes transketolase and transaldolase. These two products are intermediates of glycolysis. Therefore, these reactions provide a link between the pentose phosphate pathway and glycolysis. The outline reactions are shown below. 

As indicated earlier, the enthalpy balance method is a valuable tool for making an account of the pathways operating during cellular metabolism (reviewed by Kemp, 1993). In this way, it was shown by Eftimiadi and Rialdi (1982) that 36% of the heat dissipation by human neutrophils was due to the pentose phosphate pathway and the remainder (64%) to glycolysis, resulting in lactate production. The enthalpy recovery of 1.0 indicated that there was no measurable respiration, which is consistent with the almost complete absence of mitochondria from these cells. 

These four steps constitute the first phase of the pentose phosphate pathway and result in the consumption of one molecule of glucose 6-phosphate and the formation of one molecule of ribose 5-phosphate, two of NADPH, and one of C02. 

Becker J, Klopprogge C, Zelder O et al (2005) Amplified expression of fructose 1, 6-bispho-sphatase in Corynebacterium glutamicum increases in vivo flux through the pentose phosphate pathway and lysine production on different carbon sources. Appl Environ Microbiol 71 8587-8596... 

Stryer, L. (1995). Pentose Phosphate Pathway and Glu-coneogenesis Biosynthesis of Amino Acids and Heme. In Biochemistry, 4th ed. New York Freeman. 

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