During prolonged exercise, oxaloacetate is drained toward gluconeogenesis faster than acetyl-CoA enters the cycle. The principal anaplerotic enzyme that replenishes oxaloacetate is:

• A Pyruvate dehydrogenase
• B Pyruvate carboxylase ✓
• C Glutamate dehydrogenase
• D Propionyl-CoA carboxylase

Explanation

Pyruvate carboxylase, a biotin-dependent mitochondrial enzyme, carboxylates pyruvate to oxaloacetate using CO2 and ATP, and is activated allosterically by acetyl-CoA. This feedback ensures that when acetyl-CoA accumulates because oxaloacetate is limiting, more oxaloacetate is made. Propionyl-CoA carboxylase supplies succinyl-CoA from odd-chain fatty acids and valine but is not the principal route, and glutamate dehydrogenase feeds alpha-ketoglutarate.

Reference: Marks' Basic Medical Biochemistry, 5th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.