Glucose 6-phosphate oxidation

An excess of PGD is added to the reaction mixture containing glucose 6-phosphate and NADP to assure that 2 moles of NADPH are produced per mole of glucose-6-phosphate oxidized (109). This method has been improved by Nicholson et. al (110) to make... 

C8. Cori, O., and Lipmann, F., The primary oxidation product of enzymatic glucose-6-phosphate oxidation. ]. Biol. Chem. 194, 417-425 (1952). 

H17. Horecker, B. L., and Smymiotis, P. Z., Reversibility of glucose-6-phosphate oxidation. Biochim. et Biophys. Acta 12, 98-102 (1953). 

The oxidative portion of the pentose phosphate pathway consists of three reactions that lead to the formation of ribulose 5-phosphate, C02, and two molecules of NADPH for each molecule of glucose 6-phosphate oxidized (Figure 13.2). This portion of the pathway is particularly important in the liver and lactating mammary glands, which are active in the biosynthesis of fatty acids, in the adrenal cortex, which is active in the NADPH-dependent synthesis of steroids, and in erythrocytes, which require NADPH to keep glutathione reduced. 

At this point the metabolic function of the sequence, when it is serving to supply electrons for biosynthesis, is fulfilled. Two molecules of NADPH are generated for each molecule of glucose-6-phosphate oxidized. It is only necessary to convert ribulose-5-phosphate, the end product of the... 

The preceding reactions yield two molecules of NADPH and one molecule of ribose 5-phosphate for each molecule of glucose 6-phosphate oxidized. However, many cells need NADPH for reductive biosyntheses much more than they need ribose 5-phosphate for incorporation into nucleotides and nucleic acids. In these cases, ribose 5-phosphate is converted into glyceraldehyde 3-phosphate and fructose 6-phosphate by transketolase and transaldolase. These enzymes create a reversible link between the pentose phosphate pathway and glycolysis by catalyzing these three successive reactions. 

In the payoff phase, each of the two molecules of glyceraldehyde 3-phosphate derived from glucose undergoes oxidation at C-l the energy of this oxidation reaction is conserved in the formation of one NADH and two ATP per triose phosphate oxidized. The net equation for the overall process is... 

H. E. van Dam, A. P. G. Kieboom, and H. van Bekkum, Platinum/carbon oxidation catalysts. 7. Glucose-1-phosphate oxidation on platinum-on-carbon catalysts side-reactions and effects of catalysts structure on selectivity, Reel. Trav. Chim. Pays-Bas, 108 (1989) 404 107. 

ATP An Energy Source When glucose is oxidized in the living cell, the energy released is used to synthesize adenosine triphosphate (ATP), an anhydride of phosphoric acid. As with most anhydrides, hydrolysis of ATP is highly exothermic. The hydrolysis products are adenosine diphosphate (ADP) and inorganic phosphate. 

NADPH is produced during the transfer of acetyl groups from the mitochondrion, when malate is oxidized to pyruvate and carbon dioxide [see Fig. 13-8 and reaction (c) in the accompanying text], NADPH is also produced when glucose is oxidized and decarboxylated to ribulose 5-phosphate (Chap. 11). 

Glucose is oxidized in the pentose phosphate pathway (Chap. 11), to produce NADPH that can enter cholesterol synthesis. One molecule of glucose is required per molecule of lanosterol synthesized. (The reactions that convert lanosterol to cholesterol are outside the scope of Chap. 13.)... 

A related oxidation reaction is catalyzed by glucose-6-phosphate dehydrogenase, the enzyme that originally attracted Warburg s attention and led to the discovery of NADP. The subsfrafe, the hemiacetal ring form of glucose, is oxidized fo a lactone which is then hydrolyzed to 6-phosphogluconate (Eq. 15-10). This oxidation of an aldehyde to a carboxylic acid is not linked directly to ATP synthesis as in Fig. 15-6. 

Overall, when 1 mole of glucose is oxidized to C02 and H20, approximately 36 moles of ATP are produced if the glycerol phosphate shuttle is used, or 38 moles if the malate aspartate shuttle is used. 

X 6-Phosphogluconate is produced by the first oxidative reaction in the pentose phosphate pathway, in which carbon 1 of glucose is oxidized to a carboxylate. In contrast, glucuronic acid is oxidized at carbon 6 to the carboxylate form. 

Mono- and diesters are essential to life and represent some of the most important biological molecules. An example of an important monoester is glucose-6-phosphate, which represents the first intermediate compound formed when glucose is oxidized to supply energy for the body (Chapter 13) ... 

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