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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.

Contents

Uses

Phases

Oxidative phase

Non-oxidative phase

See also

References

External links

Uses

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.
It is also used to generate hydrogen peroxide for phagocytes.^[1]

Phases

Oxidative phase

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 entire set of reactions can be summarized as follows:

'Reactants'	'Products'	'Enzyme'	'Description'
Glucose 6-phosphate + NADP+	→ 6-phosphoglucono-δ-lactone + 'NADPH'	glucose 6-phosphate dehydrogenase	Dehydrogenation. The hydroxyl group located on carbon 1 of glucose 6-phosphate is converted into a keto group, and in the process, NADPH is generated.
6-phosphoglucono-δ-lactone + H2O	→ 6-phosphogluconate + H+	6-phosphoglucolactonase	Hydrolysis
6-phosphogluconate + NADP+	→ ribulose 5-phosphate + 'NADPH' + CO2	6-phosphogluconate dehydrogenase	Oxidative decarboxylation. NADP+ is the electron acceptor, generating another molecule of NADPH.
ribulose 5-phosphate	ribose 5-phosphate	Phosphopentose isomerase	Isomerization. (Can also be considered part of nonoxidative phase)

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

Non-oxidative phase

'Reactants'	'Products'	'Enzymes'
ribulose 5-phosphate	→ ribose 5-phosphate	phosphopentose isomerase
ribulose 5-phosphate	→ xylulose 5-phosphate	phosphopentose epimerase
xylulose 5-phosphate + ribose 5-phosphate	→ glyceraldehyde 3-phosphate + sedoheptulose 7-phosphate	transketolase
sedoheptulose 7-phosphate + glyceraldehyde 3-phosphate	→ erythrose 4-phosphate + fructose 6-phosphate	transaldolase
xylulose 5-phosphate + erythrose 4-phosphate	→ glyceraldehyde 3-phosphate + fructose 6-phosphate	transketolase

See also

★ G6PDH deficiency - A hereditary disease which disrupts the pentose phosphate pathway.

★ NADPH

★ RNA

References

1.

External links

★ The chemical logic behind the pentose phosphate pathway

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