Fructose-1,6-bisphosphatase deficiency presents in infants with hypoglycaemia, lactic acidosis, and hepatomegaly precipitated by fasting or fever. The enzyme catalyses which irreversible gluconeogenic step?

• A Conversion of glucose-6-phosphate to glucose
• B Conversion of fructose-1,6-bisphosphate to fructose-6-phosphate ✓
• C Conversion of oxaloacetate to phosphoenolpyruvate
• D Conversion of pyruvate to oxaloacetate

Explanation

Fructose-1,6-bisphosphatase (FBPase-1) catalyses the hydrolysis of fructose-1,6-bisphosphate to fructose-6-phosphate + Pi, one of four irreversible gluconeogenic bypass reactions. Deficiency blocks gluconeogenesis from lactate, amino acids, and glycerol; during fasting, blood glucose falls while lactate (from Cori cycle) accumulates, causing lactic acidosis. Glycogenolysis can temporarily maintain glucose, explaining why longer fasting is needed to trigger symptoms. Glucose-6-phosphatase dephosphorylates glucose-6-phosphate (deficient in GSD Ia). PEPCK converts OAA to PEP. Pyruvate carboxylase converts pyruvate to OAA.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.