Pentose Phosphate Pathway

Question 1

describe purpose of pentose phosphate pathway

Answer 1

• occurs in cytosol of cells
• alternate pathway for metabolism of glucose
  
  • doesn’t produce energy
• PPP provides:
  
  • NADPH + H+
  • pentoses

Question 2

describe when PPP is active

Answer 2

• erythrocytes (provide NADPH for the reduction of glutathione)
• white blood cells and macrophages (provides NADPH for phagocytosis)

Question 3

contrast the oxidative phase and the nonoxidative phase

Answer 3

• oxidative phase:
  
  • irreversible rxns
  • forms NADPH and pentose phosphate
  • enzymes are dehydrogenases (G6PD)
• nonoxidative phase:
  
  • reversible rxns
  • takes place under conditions where pentoses are not required by cells
  • involves interconversion of sugars resulting in the formation of glycolytic intermediates
  • enzymes are transketolase (TPP) and transaldolase

Question 4

describe the oxidative phase of pathway

Answer 4

Question 5

describe the interconversion of pentoses in the nonoxidative phase

Answer 5

Question 6

describe the formation of fructose 6-P

Answer 6

Question 7

describe the uses of NADPH (for this course only)

Answer 7

• reduction and detoxification of H2O2
• phagocytosis in WBCs

Question 8

describe phagocytosis by WBCs

Answer 8

• during phagocytosis, superoxide free radicals are generated using NADPH oxidase (requires NADPH) in the WBCs
• Deficiency of NADPH oxidase causes chronic granulomatous disease characterized by severe persistent infections
• infections result in increased production of oxidants

Question 9

describe the detoxification of H2O2

Answer 9

• in RBCs, H2O2 is detoxified to H2O by glutathione peroxidase
• the oxidized glutathione is converted back to the reduced form by glutathione reductase, utilizing NADPH generated by the PPP
• in RBCs, GSH is the major antioxidant to detoxify H2O2
• defect in the PPP results in accumulation of H2O2
  
  • causes damage to RBC membrane –> hemolysis

Question 10

describe G6PD deficiency

Answer 10

• decrease in the detoxification of free radicals and peroxides formed in cells (results in hemolysis)
• GSH is required for maintenance of SH groups in proteins. G6PD deficiency can result in formation of denatured proteins as insoluble masses (Heinz bodies)
• G6PD deficiency occurs in all cells, but is most severe in RBCs since PPP is only source of NADPH

Question 11

name stressors of G6PD

Answer 11

• infections
• oxidant drugs (sulfa drugs, primaquine)
• fava beans