The Phosphogluconate Pathway

Pentose Phosphate Pathway It is also called as Hexose Monophosphate shunt or Phosphogluconate pathway of glucose oxidation. Definition - It is a shunt pathway of oxidation of glucose. It is a metabolic pathway that generates NADPH. It is also plays an important role in synthesis of pentoses. It takes place mainly in the cytosol of the cell. Six carbon compound: Glucose-6-phosphate is the starting compound of this pathway. Pentose Phosphate Pathway Also called as Hexose Monophosphate shunt or Phosphogluconate pathway of glucose oxidation. Definition - It is a shunt pathway of oxidation of glucose. It is a metabolic pathway that generates NADPH. It is also plays an important role in synthesis of pentoses. It takes place mainly in the cytosol of the cell. Six carbon compound: Glucose-6-phosphate is the starting compound of this pathway. Oxidative Phase: Glucose-6-phosphate is oxidized to 6-phosphogluconolactone by NADP+-linked dehydrogenase. 6-phosphogluconolactone is hydrolyzed to 6-phosphogluconate. 6-phosphogluconate is oxidized and decarboxylated by NADP+-linked 6-phosphogluconate dehydrogenase. This reaction produces ribulose-5-phosphate and CO2. Non-oxidative Phase: Ribulose-5-phosphate is isomerized to ribose-5-phosphate. Ribose-5-phosphate can be converted to ribose-5-phosphate or xylulose-5-phosphate. Xylulose-5-phosphate can be converted to xylulose-5-phosphate or ribose-5-phosphate. These interconversions involve a series of reactions catalyzed by transketolase and transaldolase enzymes. Finally, fructose-6-phosphate and glyceraldehyde-3-phosphate are produced, which can enter glycolysis. Pentose Phosphate Pathway Glucose-6-phosphate is oxidized to 6-phosphogluconolactone by NADP+-linked dehydrogenase. 6-phosphogluconolactone is hydrolyzed to 6-phosphogluconate. 6-phosphogluconate is oxidized and decarboxylated by NADP+-linked 6-phosphogluconate dehydrogenase. This reaction produces ribulose-5-phosphate and CO2. Non-oxidative phase: Ribulose-5-phosphate is isomerized to ribose-5-phosphate. Ribose-5-phosphate can be converted to ribose-5-phosphate or xylulose-5-phosphate. Xylulose-5-phosphate can be converted to xylulose-5-phosphate or ribose-5-phosphate. These interconversions involve a series of reactions catalyzed by transketolase and transaldolase enzymes. Finally, fructose-6-phosphate and glyceraldehyde-3-phosphate are produced, which can enter glycolysis. Significance: NADPH is a powerful reducing agent, essential for various biosynthetic reactions. The pathway provides ribose-5-phosphate for nucleotide synthesis. It plays a role in the metabolism of pentoses derived from the diet. Pentose Phosphate Pathway Oxidative Phase: Glucose-6-phosphate dehydrogenase: Glucose-6-phosphate is oxidized to 6-phosphogluconolactone using NADP+ as a cofactor. Lactonase: 6-phosphogluconolactone is hydrolyzed to 6-phosphogluconate. 6-phosphogluconate dehydrogenase: 6-phosphogluconate is oxidized and decarboxylated to ribulose-5-phosphate, producing NADPH and CO2. Non-oxidative phase: Isomerase: Ribulose-5-phosphate is isomerized to ribose-5-phosphate. Transketolase: Ribose-5-phosphate and xylulose-5-phosphate undergo a transketolase reaction to form glyceraldehyde-3-phosphate and sedoheptulose-7-phosphate. Transaldolase: Sedoheptulose-7-phosphate and glyceraldehyde-3-phosphate react to form erythrose-4-phosphate and fructose-6-phosphate. Transketolase: Erythrose-4-phosphate and xylulose-5-phosphate react to form glyceraldehyde-3-phosphate and fructose-6-phosphate. Overall Reaction: Glucose-6-phosphate + 2 NADP+ + H2O → 2 NADPH + 2 H+ + CO2 + fructose-6-phosphate + glyceraldehyde-3-phosphate