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The pentose phosphate pathway (also called Phosphogluconate Pathway, or Hexose Monophosphate Shunt [HMP shunt]) is a process that serves to generate NADPH and the synthesis of pentose (5-carbon) sugars. There are two distinct phases in the pathway. The first is the oxidative phase, in which NADPH is generated, and the second is the non-oxidative synthesis of 5 carbon sugars. The pathway is one of the three main ways the body creates molecules with reducing power, accounting for approximately 10% of NADPH production in humans.

One of the uses of NADPH in the cell is to prevent oxidative stress. It reduces the coenzyme glutathione which converts reactive H₂O₂ into H₂O. If absent, the H₂O₂ would be converted to hydroxyl free radicals which can attack the cell.

Contents 1 Oxidative phase 2 Non-oxidative phase 3 See also 3.1 External links 4 References

In this phase, two molecules of NADP⁺ are reduced to NADPH, utilising the energy from the conversion of glucose-6-phosphate into ribulose 5-phosphate.

The overall reaction for this process is:
Glucose 6-phosphate + 2 NADP⁺ + H₂O → ribulose 5-phosphate + 2 NADPH + 2 H⁺ + CO₂

The first step in this series of reactions is the dehydrogenation of glucose 6-phosphate into 6-phosphoglucono-δ-lactone. This reaction is catalyzed by glucose 6-phosphate dehydrogenase. The hydroxyl group located on carbon 1 of glucose 6-phosphate is converted into a keto group, and in the process, NADPH is generated.

The second step is the hydrolysis of 6-phosphoglucono-δ-lactone to 6-phosphogluconate, which is catalyzed by 6-phosphoglucolactonase.

The third step is the oxidative decarboxylation of 6-phosphogluconate to ribulose 5-phosphate. This reaction is catalyzed by 6-phosphogluconate dehydrogenase and NADP⁺ is the electron acceptor, generating another molecule of NADPH.

The final step is the isomerization (catalyzed by phosphopentose isomerase) of ribulose 5-phosphate into ribose 5-phosphate.

The entire set of reactions can be summarized as follows:

1. Glucose 6-phosphate + NADP+ → 6-phosphoglucono-δ-lactone + NADPH
2. 6-phosphoglucono-δ-lactone + H₂O → 6-phosphogluconate + H⁺
3. 6-phosphogluconate + NADP⁺ → ribulose 5-phosphate + NADPH + CO₂

1. ribulose 5-phosphate → ribose 5-phosphate (phosphopentose isomerase)
2. ribulose 5-phosphate → xylulose 5-phosphate (phosphopentose epimerase)
3. xylulose 5-phosphate + ribose 5-phosphate → glyceraldehyde 3-phosphate + sedoheptulose 7-phosphate (transketolase)
4. sedoheptulose 7-phosphate + glyceraldehyde 3-phosphate → erythrose 4-phosphate + fructose 6-phosphate (transaldolase)
5. xylulose 5-phosphate + erythrose 4-phosphate → glyceraldehyde 3-phosphate + fructose 6-phosphate (transketolase)

For a thorough scientific overview of ribose-5-phosphate isomerase deficiency and transaldolase deficiency, one can consult the supplement of chapter 73 in OMMBID.^[1] For more online resources and references, see inborn error of metabolism.

• G6PDH deficiency - A hereditary disease which disrupts the pentose phosphate pathway.
• NADPH
• RNA

• The chemical logic behind the pentose phosphate pathway

1. ^ Charles Scriver, Beaudet, A.L., Valle, D., Sly, W.S., Vogelstein, B., Childs, B., Kinzler, K.W. (2006). The Online Metabolic and Molecular Bases of Inherited Disease. New York: McGraw-Hill. - Free summaries of 255 chapters, full text through many universities and organizations. There is also the OMMBID blog.

v • d • e Metabolism: carbohydrate metabolism
Fermentation (Ethanol, Lactic acid) - Gluconeogenesis - Glycogenolysis - Glycolysis - Pentose phosphate pathway - Photosynthesis (Carbon fixation) Carbohydrate catabolism

v • d • e Metabolism map

Glucuronate metabolism Pentose interconversion Inositol metabolism Cellulose and sucrose metabolism Starch and glycogen metabolism Other sugar metabolism Pentose phosphate pathway Glycolysis and Gluconeogenesis Amino sugars metabolism Small amino acid synthesis Branched amino acid synthesis Purine biosynthesis Histidine metabolism Aromatic amino acid synthesis Pyruvate decarboxylation Anaerobic respiration Fatty acid metabolism Urea cycle Aspartate amino acid group synthesis Porphyrins and corrinoids metabolism Citric acid cycle Glutamate amino acid group synthesis Pyrimidine biosynthesis  v • d • e  All pathway labels on this image are links, simply click to access the article. A high resolution labeled version of this image is available here.