In gluconeogenesis, the transport of oxaloacetate from mitochondria to cytosol is required because PEPCK is primarily cytosolic. Oxaloacetate itself cannot cross the inner mitochondrial membrane. The molecule in which oxaloacetate carbon equivalents are exported to the cytosol is:
- A Malate ✓
- B Citrate
- C Succinate
- D Alpha-ketoglutarate
Correct answer: A. Malate
Explanation
Oxaloacetate (OAA) is first reduced to malate by mitochondrial malate dehydrogenase (using NADH). Malate then crosses the inner mitochondrial membrane via the malate-aspartate shuttle/dicarboxylate transporter. In the cytosol, malate is re-oxidised to OAA by cytosolic malate dehydrogenase, generating NADH needed for the glyceraldehyde-3-phosphate dehydrogenase step of gluconeogenesis. PEPCK then decarboxylates/phosphorylates OAA to phosphoenolpyruvate. Citrate is used to export acetyl-CoA for fatty acid synthesis, not for gluconeogenesis from OAA.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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