Pentose Phosphate Pathway Flashcards
Essential Pentosuria
-Rare, benign genetic condition
- Lack of xylulose reductase (reduces xylulose to xylitol in uronic acid pathway)
- Result = ↑ xylulose in urine
Alimentary Pentosuria
Occurs after consumption of large amounts of fruits (e.g. pears)
High fructose consumption
- Fructose bypasses reaction catalyzed by Phosphfructokinase —> undergoes more rapid glycolysis than glucose
- Results: ↑ FAs, VLDL (atherosclerosis)
- Results: ↓ ATP synthesis, ↑ uric acid formation (gout)
Essential fructosuria
- Lack of hepatic fructokinase
- Benign, asymptomatic
Hereditary fructose intolerance
- Lack of aldolase B
- Severe hypoglycemia and vomiting after fructose consumption
Treatment: Diet low in fructose, sorbitol, sucrose
Galactosemia
- Inability to metabolize galactose due to defects of galactokinase, uridyl transferase, or 4-epimerase
- Instead: converted to galactitol
- Galactitol accumulates in lens of the eye –> cataract
- Liver failure and mental deterioration
Treatment: Galactose-free diet
Hemolytic anemia
- Genetic deficiency of glucose-6-phosphate dehydrogenase (1st enzyme in PPP)
-RBCs destroyed when individual subjected to oxidative stress
- Gluathione peroxidase reliant on NADPH
Oxidative (Irreversible) Beginning & End
Glucose-6-Phosphate → Ribulose -5-Phosphate
Nonoxidative (Reversible) Beginning & End
Ribulose-5-Phosphate → Glucose-6-Phosphate
Oxidative, Irreversible Pathway (NADPH formation)
- Glucose-6-Phosphate → 6-Phosphogluconolactone (NAPH FORMATION)
Enzyme: Glucose-6-Phosphate Dehydrogenase
- NADP+ → NADPH + H+
- 6-Phosphogluconolactone → 6-Phosphogluconate
Enzyme: Gluconolactone Hydrolase
-Requires Water
- 6-Phosphogluconate → 3-keto 6-phosphogluconate (NAPH FORMATION)
Enzyme: 6-phosphogluconate dehydrogenase
- NADP+ → NADPH + H+
- 3-keto 6-phosphogluconate → Ribulose-5-phosphate
Enzyme: 6-phosphogluconate dehydrogenase
- CO2 released.
Nonoxidative, Reversible Pathway (Ribose formation)
- Ribulose-5-phosphate → Xylulose-5-Phosphate
Enzyme: Ribulose-5-Phosphate 3-Epimerase
- Ribulose-5-phosphate → Endiol form → Ribose-5-Phosphate (RIBOSE FORMATION)
Enzyme: Ribose-5-Phosphate Ketoisomerase
- Ribulose-5-phosphate + Xylulose-5-Phosphate → Sedoheptulose-7-phosphate & Glyceraldehyde-3-Phosphate
Enzyme: Transketolase
- Sedoheptulose-7-phosphate + Glyceraldehyde-3-Phosphate → Fructose-6-Phosphate + Erythrose-4-Phosphate
Enzyme: Transaldolase
- Eryhrose-4-Phosphate + Xylulose-5-Phosphate → Fructose-6-Phosphate + Glyceraldehyde-3-Phosphate
Enzyme: Transketolase
Name five tissues in which the PPP is active
Liver
Adipose Tissue
Adrenal Cortex
Thyroid
RBCs
Testis
Lactating Mammary Gland
PPP Basics
Location: Cytosol
Metabolic Pathway for Glucose
Glucose-6-Phosphate
Used NADP+
Produces CO2
Glycolysis Basics
Location: Cytosol
Metabolic Pathway for Glucose
Glucose-6-Phosphate
Used NAD+
Generates ATP
PPP & Glycolysis Linked by
Xylulose-5-Phosphate
Xyluose-5-Phosphate Functions
o Activates kinase, Inactivates Phosphatase
o ↑ Fructose 2,6-bisphosphate formation
o ↑ Phosphofructokinase activity
o ↑ Glycolysis
Uronic Acid Pathway
Location: Liver
Products: Glucose → Glucuronic Acid & Pentoses
Does not produce ATP
Function: Glucuronate is precursor to proteoglycans and need for drug metabolism
NADPH used for synthesis of…
Fatty Acids (NADPHATTY ACIDS)
Steroids
Amino Acids
Even tissues with low PPP activity can synthesize ribose-5-phosphate via ____
reversal of nonoxidative phase utilizing fructose-6-phosphate.
How does Xyulose-5-Phosphate link glycolysis and the PPP
- Activates kinase needed for glycolysis
- Inactivates phosphatase enzyme needed for gluconeogenesis
_____ needed to convert glyceraldehyde 3-phosphate to glucose-6-phosphate
Fructose 1,6 bisphosphate
