Pentose phosphate pathway Flashcards
Glucose-6-phosphate dehydrogenase
3 Glucose-6-phosphate + 3NADP –> 6-phosphoglucono-∂-lactone + 3 NADPH + 3H
1st oxidative reaction
irreversible
highly regulated
6-Phosphogluconolactonase
3 6-phosphogluconolactonase-∂-lactone + 3H2O –> 3 6-phosphogluconate + 3H+
2nd Oxidative reactions
6-phosphogluconate dehydrogenase
3 6-phosphogluconate + 3NADP –> 3 ribulose-5-phosphate + 3NADPH + 3CO2
Isomerization and epimerization overall reaction
3 Ribulose-5Phosphate ribose-5-phosphate + 2 Xylulose-5-phosphate
ribulose-5-phosphate isomerase
ribulose-5-phosphate ribose-5-phosphate
4th step
ribulose-5-phosphate epimerase
2 Ribulose-5-phosphate 2 Xylulose-5-phophate
5th step
C-C bond clevage and formation overall reaction
R5P + 2Xu5P 2F6P + GAP
3 C5 2 C6 + C3
transketolase
1) ribose-5-phosphate + xylulose-5-phosphate –> sedoheptulose-7-phosphate + glyceraldehyde-3-phosphate
- Reaction 6
2) Xylulose-5-phosphate + Erythrose-4-phosphate –> Fructose-6-phosphate + Glyceraldehyde-3-phosphate –≥ glycolysis
- 8th reaction (last)
Transaldolase
Glyceraldehyde-3-phosphate + Sedheptulose-7-phosphate –> fructose-6-phosphate + erythrose-4-phosphate.
-7th reaction
Overall pentose phosphate pathway
3 G6P + 6NADP + 3H2O –> 6NADPH + 6H+ + 3CO2 + 2F6P + G3P
Role of NADPH in Red blood cells
1) 2 glutathione (GSH) + organic hydroperoxide (ROOH) –>(glutathione peroxidase) gutathione disulfide (GSSG) + ROH + H2O
2) GSSG + NADPH + H+ –> (glutathione reductase) 2GSH + NADP
Glucose-6-phosphate dehydrogenase deficiency
Most common enzymopathy
- Deficiency in G6PDH –> less NADPH production –> less ability to keep GSH high –> cannot handle extra oxidant (damage to cell membrane) –> hemolytic anemia (break down of RBC, jaundice)
- Self limiting: high H2O2 –> lysis of RBC –> Stimulation of young red blood cell release to cope with oxidative stress.
Overall reaction
3 G-6-P + 6NADP + 3H2O –> 6NADPH + 6H+ + 3CO2 + 3Ru5P
