Updated: 8/7/2021

HMP Shunt

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Overview

  • Function 
    • generate NADPH
      • required for FA synthesis, steroid synthesis, reduction of oxidizing agents (H2O2 see figure)
    • provide ribose 5-phosphate
      • required for nucleotide synthesis
  • Pathway
    • occurs in cytoplasm of all cells
    • no ATP consumed or generated
    • 2 phases
      • oxidative
        • produces NADPH
        • glucose 6-phosphate (G6P) → 6-phosphogluconate
          • catalyzed by glucose 6-phosphate dehydrogenase (G6PDH)
            • rate limiting step
            • activated by NADP+, insulin
            • inhibited by NADPH
        • irreversible
      • nonoxidative
        • exchanging intermediate substrates between glycolysis and HMP shunt
          • catalyzed by transketolase 
            • requires thiamine
        • reversible
  • Clinical relevance
    • glucose-6-phosphate dehydrogenase (G6PDH) deficiency   
      • pathophysiology
        • ↓ NADPH production
          • cells (specifically RBCs) lose protection against oxidizing agents
            • cannot regenerate glutathione
        • XR
        • most common human enzyme deficiency
        • ↑ prevalence among blacks
          • ↑ malarial resistance
            • by shortening the circulation life of RBCs
              • Plasmodium does not have enough time for life span
            • plasmodium does not have defense against free radicals
              • ↑ in free radicals kills parasite
      • presentation
        • episodic hemolytic anemia
          • intravascular hemolysis
          • normocytic
          • 2-3 days post precipitating stress
            • foods
              • fava beans
                • common in Mediterranean foods
                • presentation
                  • pallor, hemoglobinuria 24-48 post ingestion
            • drugs
              • sulfonamides, primaquine, antituberculosis drugs
            • infection
              • free radicals generated by the immune system
        • Heinz bodies  
          • oxidized hemoglobin that precipitates within RBCs
        • bite cells  
          • result from the phagocytic removal of Heinz bodies by macrophages 
        • back pain
      • test
        • active hemolysis screen
          • Heinz body prep 

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Questions (4)
Evidence (2)
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EXPERT COMMENTS (9)
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