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Pentose Phosphate

Pentose Phosphate. CH339K. Pentose Phosphate. An example of a pathway that can be both: Anabolic Generates ribose-5-phosphate for nucleotide synthesis Metabolizes dietary pentoses into glycolytic / gluconeogenic intermediates. Catabolic Generates reducing power (NADPH )

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Pentose Phosphate

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  1. Pentose Phosphate CH339K

  2. Pentose Phosphate An example of a pathway that can be both: • Anabolic • Generates ribose-5-phosphate for nucleotide synthesis • Metabolizes dietary pentoses into glycolytic/gluconeogenic intermediates. • Catabolic • Generates reducing power (NADPH) • Can completely oxidize glucose • Can carry on into glycolysis Aka HexoseMonophosphate Shunt

  3. NADH vs NADPH As a general rule of thumb: • NAD+/NADH is used in catabolic processes • NADP+/NADPH is used in anabolic processes

  4. G3P to Glycolysis

  5. Oxidative Phase Lose a carbon Reduce 2 NADP+ lactonase H2O

  6. Better Picture

  7. Glutathione -SH containing tripeptide Glu-Cys-Gly Amino of Cysteine linked to g-carboxyl of glutamate Commonly used for reducing agent in cells Oxidizes to for disulfide-linked GSSG Rereduced to GSH using NADPH

  8. 2 GSH NADP+ Glutathione Reductase NADPH + H+ GSSG

  9. Making Glutathione • For the Reaction to form GSH: We can figure out DGo from what we learned about redox reactions

  10. For what it’s worth… Divicine is found in fava beans and some other legumes Favas (broad beans) are common foodstuffs in the old world. Largest production in Europe and China. The parent plant, Vicia faba, is among the oldest cultivated plants - ~6,000 years.

  11. Glucose-6-P Dehydrogenase Deficiency • Effects ~ 4*108 people worldwide • Most common human genetic disease • X-linked • Lack of G-6PD means lack of NADPH • Lack of NADPH means lack of GSH • Lack of GSH means excess of peroxides • RBC membranes particularly susceptible to peroxides • Hemolytic Anemia

  12. Glucose-6-Phosphate Dehydrogenase Deficiency Cappellini, M.D., and Fiorelli, G. (2008) Glucose-6-phosphate dehydrogenase deficiency, Lancet371: 64-74.

  13. Harmful Agents for G6PDD Sufferers

  14. G3P to Glycolysis

  15. Non-oxidative phase

  16. Ribulose can be used to make ribose • enediol intermediate phosphopentose isomerase

  17. Transketolase moves 2-carbon units

  18. Transaldolase moves 3-carbon units Lack of transketolase can cause hepatosplenomegaly and liver cirrhosis in childhood. Verhoeven, N. M. et al (2001) Transaldolase Deficiency: Liver Cirrhosis Associated with a New Inborn Error in the Pentose Phosphate Pathway , Amer. J. Hum. Gen. 68(5): 1086-1092.

  19. Transketolase uses a TPP cofactor 1. 2.

  20. Transaldolase forms a protonated Schiff base

  21. Control • Conversion of glucose-6-Pi to the lactone is essentially irreversible. • The enzyme, glucose-6-phosphate dehydrogenase, controls the rate of the pathway. • NADPH competes with NADP for binding in he active site; • ATP competes with glucose-6-phosphate. • At high [NADPH] and/or high [ATP], entrance into the pathway is restricted.

  22. Multiple Functions of Pentose Phosphate Pathway

  23. Products in the pathway can be withdrawn at several points

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