The '''pentose phosphate pathway''' (also called Phosphogluconate Pathway, or Hexose Monophosphate 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 reducing molecules to prevent Oxidative_stress, accounting for approximately 10% of NADPH production in humans. ==Oxidative phase== In this phase, two molecules of NADP⁺ are reduced to NADPH, utilising the energy from the conversion of Glucose 6-Phosphate into Ribose 5-phosphate. The overall reaction for this process is:
Glucose 6-phosphate + 2 NADPH⁺ + H₂O → ribose 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 a ''lactonase''. 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: #Glucose 6-phosphate + NADP+ → 6-phosphoglucono-δ-lactone + NADPH #6-phosphoglucono-δ-lactone + H₂O → 6-phosphogluconate + H⁺ #6-phosphogluconate + NADP⁺ → ribulose 5-phosphate + NADPH + CO₂ Image:PentosePhosphatePathway-OxidativeNADPH.png ==Synthesis of sugar== ==Non-oxidative phase== #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 (transaldolase) ==See also== * G6PDH deficiency - A hereditary disease which disrupts the pentose phosphate pathway. * NADPH * RNA ===External links=== *The chemical logic behind the pentose phosphate pathway Category:Metabolism De:Pentosephosphatweg Fr:Voie_des_pentoses He:מסלול_הפנטוז_פוספט