Pathway
Pentose phosphate pathway
The pentose phosphate pathway is responsible for the generation of a substantial fraction of the cytoplasmic NADPH required for biosynthetic reactions, and for the generation of ribose 5-phosphate for nucleotide synthesis. Although the pentose phosphate pathway and glycolysis are distinct, they involve three common intermediates, glucose 6-phosphate, glyceraldehyde 3-phosphate, and fructose 6-phosphate, so the two pathways are interconnected. The pentose phosphate pathway consists of eight reactions:1. Conversion glucose 6-phosphate to D-glucono-1,5-lactone 6-phosphate, with the formation of NADPH; 2. Conversion of D-glucono-1,5-lactone 6-phosphate to 6-phospho-D-gluconate; 3. Conversion of 6-phospho-D-gluconate to ribulose 5-phosphate, with the formation of NADPH; 4. Conversion of ribulose 5-phosphate to xylulose 5-phosphate; 5. Conversion of ribulose 5-phosphate to ribose 5-phosphate; 6. Rearrangement of ribose 5-phosphate and xylulose 5-phosphate to form sedoheptulose 7-phosphate and glyceraldehyde 3-phosphate; 7. Rearrangement of sedoheptulose 7-phosphate and glyceraldehyde 3-phosphate to form erythrose 4-phosphate and fructose 6-phosphate; and 8. Rearrangement of xylulose 5-phosphate and erythrose 4-phosphate to form glyceraldehyde 3-phosphate and fructose-6-phosphate.
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The oxidative branch of the pentose phosphate pathway, reactions 1-3, generates NADPH and pentose 5-phosphate. The non-oxidative branch of the pathway, reactions 4-8, converts pentose 5-phosphate to other sugars.
The overall pathway can operate to generate only NADPH (glucose 6-phosphate is converted to pentose 5-phosphates, which are directed to the synthesis of fructose 6-phosphate and glyceraldehyde 3-phosphate, which in turn are converted back to glucose 6-phosphate). The reactions of the non-oxidative branch can operate to generate net amounts of ribose 5-phosphate with no production of NADPH. Net flux through this network of reactions appears to depend on the metabolic state of the cell and the nature of the biosynthetic reactions underway.
G6PD, the enzyme that catalyzes the first reaction of the pathway, is more extensively mutated in human populations than any other enzyme, pehaps because these mutant alleles confer malaria resistance. Mutations affecting other parts of the pathway are rare, though several have been described and studies of their effects have contributed to our understanding of the normal flux of metabolites through this network of reactions.
What the reference databases state
Statements
15 statements
15 statements · 1 reference database · Subject: Pentose phosphate pathway · Sources: Reactome
- DERA participates in Pentose phosphate pathwayProteinReactome R-HSA-71336Inferred only
- G6PD participates in Pentose phosphate pathwayProteinReactome R-HSA-71336Inferred only
- PGD participates in Pentose phosphate pathwayProteinReactome R-HSA-71336Inferred only
- PGLS participates in Pentose phosphate pathwayProteinReactome R-HSA-71336Inferred only
- PGM2 participates in Pentose phosphate pathwayProteinReactome R-HSA-71336Inferred only
- PRPS1 participates in Pentose phosphate pathwayProteinReactome R-HSA-71336Inferred only
- PRPS1L1 participates in Pentose phosphate pathwayProteinReactome R-HSA-71336Inferred only
- PRPS2 participates in Pentose phosphate pathwayProteinReactome R-HSA-71336Inferred only
- RBKS participates in Pentose phosphate pathwayProteinReactome R-HSA-71336Inferred only
- RPE participates in Pentose phosphate pathwayProteinReactome R-HSA-71336Inferred only
- RPEL1 participates in Pentose phosphate pathwayProteinReactome R-HSA-71336Inferred only
- RPIA participates in Pentose phosphate pathwayProteinReactome R-HSA-71336Inferred only
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- SHPK participates in Pentose phosphate pathwayProteinReactome R-HSA-71336Inferred only
- TALDO1 participates in Pentose phosphate pathwayProteinReactome R-HSA-71336Inferred only
- TKT participates in Pentose phosphate pathwayProteinReactome R-HSA-71336Inferred only