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Pentose Phosphate Pathway

  1. (Hexose Monophosphate Shunt)
    PPP is a multi cyclic process in which 3 molecules of glucose-6-phosphate give rise to 3 molecules of CO2 and three 5 carbon residues, the latter are rearranged to generate 2 molecules of glucose-6-phosphate and 1 mo lecule of glycolytic intermediate glyceraldehyde-3-phosphate

1.  Function:

  1. Generation of NADPH for reductive biosynthesis.
    1. Fatty acid synthesis
    2. Steroid hormones synthesis
  2. Provides a source of ribose-5-phosphate for nucleic acid biosynthesis.
  3. Erythrocytes depend on PPP for NADPH which is required to maintain glutathione in reduced state which is essential to maintain integrity of RBC membrane.
  1. Location: Cytosol of erythrocytes, liver, lactating mammary gland, adipose tissue, adrenal cortex.

Reactions of Pentose phosphate pathway:

2 Phases

  • Oxidative Non-reversible phase
  • Non-oxidative reversible phase.

Oxidative phase generates NADPH

Transketolase enzyme requires TPP as coenzymes and magnesium acts on xylulose –5-phosphate & ribose-5-phosphate converting them to sedoheptulose-7-phosphate and glyceraldehyde-3-phosphate.

  1. RBC Transketolase is used as an index of thiamine deficiency

Role of Pentose phosphate in protecting erythrocytes against hemolysis:

The Pentose phosphate Pathway in erythrocytes provide NADPH for reduction of oxidized glutathione to reduced glutathione catalyzed by glutathione reductase.  In turn, reduced glutathione removes H2 O2 from erythrocyte in a reaction catalyzed by glutathione peroxidase, an enzyme that contains the trace element selenium.


The flow chart of pentose phosphate pathway is shown below:

Fig: Flow chart of pentose phosphate pathway and its connections with the pathway of glycolysis. The full pathway, as indicated, consists of three interconnected cycles in which glucose 6-phosphate is both substrate and end-product. The reactions above the broken line are nonreversible, whereas all reactions under that line are freely reversible apart from that catalyzed by fructose 1,6-bisphosphatase.


  1. Uronic Acid Pathway
    1. Significance of Uronic Acid Pathway:
      1. Source of UDP glucose that is used for glycogen formation.
      2. Formation of Glucuronic acid for detoxifying the body.
      3. Pathway integral to formation of ascorbic acid in most animals. Humans cannot synthesis ascorbic acid due to lack of enzyme L-gulonolactone oxidase.

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