Introduction to Oxidative Phosphorylation at Substrate Level
- Oxidative phosphorylation is the metabolic pathway in which ATP (adenosine triphosphate) is synthesized by utilizing energy released by electron transport chain (ETC).
- Substrate-level phosphorylation refers to the direct transfer of phosphate group from a high-energy substrate molecule to ADP (adenosine diphosphate), forming ATP.
Oxidative Phosphorylation of Glyceraldehyde 3-Phosphate (GAP)
- GAP is an intermediate in glycolysis, produced from glucose.
- During glycolysis, GAP is oxidized to 1,3-bisphosphoglycerate (1,3-BPG) by glyceraldehyde 3-phosphate dehydrogenase.
- The oxidation of GAP results in the reduction of NAD+ to NADH.
- The energy released from this oxidation reaction drives the phosphorylation of ADP to ATP, forming 1,3-BPG.
Substrate-level phosphorylation: High energy phosphate is transferred from 1,3-bisphosphoglycerate to ADP through a reaction catalyzed by phosphoglycerate kinase.
The result is the production of 3-phosphoglycerate and ATP.
Enolase Reaction
- Enolase catalyzes the conversion of 2-phosphoglycerate (2-PG) to phosphoenolpyruvate (PEP) in glycolysis.
- This reaction involves the removal of water molecule from 2-PG to form the high-energy intermediate PEP.
- Although enolase reaction is not a direct substrate-level phosphorylation step, the high-energy PEP molecule contributes to ATP synthesis through subsequent reactions.