CARBOHYDRATE CATABOLISM - ENTNER DOUDOROFF (ED) PATHWAY

ENTNER DOUDOROFF PATHWAY

• Entner Doudoroff (ED) pathway was discovered by Entner and Doudoroff in 1952 in Pseudomonas saccharophila.
• ED pathway occurs in both aerobic and anaerobic condition.
• ED pathway occurs in cytoplasm of prokaryotes only.
• In the ED pathway, ATP was produced by Substrate level Phosphorylation.
• Only few bacteria like, Zymomonas mobilis employ the ED pathway. The alcohol productivity of Zymomonas mobilis is higher than yeast because of this fermentative pathway. 
• Other bacteria using ED pathway are Pseudomonas sp., Azotobacter sp., Rhizobium sp., Agrobacterium sp., Escherichia coli, Enterococcus faecalis, Xanthomonas campestris, Hordeum vulgare and Archaea.

ED Pathway

• Pyruvate and Glyceraldehyde-3-phosphate produced from Glucose by ED pathway.
• At first Glucose is phosphorylated to Glucose-6-phosphate by the enzyme Hexokinase.
• Glucose-6-phosphate is then oxidized to 6-Phosphogluconic acid by releasing a molecule of NADPH. This reaction is catalyzed by the enzyme Glucose-6-phosphate dehydrogenase.
• The 6-phosphogluconic acid undergoes dehydration reaction catalyzed by 6- phosphogluconate dehydratase to form 2-keto 3-deoxy 6-Phosphogluconate (KDPG).
• KDPG splits to form Pyruvate and Glceraldehyde-3-phosphate. It is catalyzed by KDPG Aldolase enzyme.
• Glyceraldehyde-3-phosphate is then metabolized by Glycolysis to form Pyruvate.
• Pyruvate is decarboxylated to Acetaldehyde, which is then reduced to Ethanol by Alcohol dehydrogenase with NADH as the electron donor. 

Significance of ED Pathway

• ED pathway used two specific enzymes ie. 6-phosphogluconate dehydratase and KDPG aldolase.
• This pathway generates 1 ATP, 1 NADH and 1 NADPH from one glucose molecule