During prolonged fasting, circulating beta-hydroxybutyrate rises markedly, yet red blood cells continue to depend entirely on glucose. The reason erythrocytes cannot utilise ketone bodies is:

• A They lack the monocarboxylate transporter required for ketone uptake
• B High intracellular 2,3-BPG allosterically inhibits succinyl-CoA:acetoacetate CoA transferase
• C They lack mitochondria, so they cannot perform the TCA cycle reactions needed to oxidise acetyl-CoA derived from ketones ✓
• D Mature erythrocytes lack SCOT (thiophorase) despite possessing mitochondria

Explanation

Ketone body utilisation requires conversion of acetoacetate to acetoacetyl-CoA by SCOT followed by thiolytic cleavage to two acetyl-CoA molecules, which must then enter the TCA cycle inside mitochondria. Mature erythrocytes contain no mitochondria and rely solely on anaerobic glycolysis regardless of fuel availability. They do express monocarboxylate transporters, and 2,3-BPG regulates haemoglobin oxygen affinity rather than ketolytic enzymes. The same mitochondrial limitation explains why corneal epithelium also spares ketones.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.