Which kinetic property distinguishes hepatic glucokinase from the hexokinase found in most other tissues?
- A Glucokinase has a lower Km for glucose and is inhibited by its product glucose-6-phosphate
- B Glucokinase has a higher Km for glucose and lacks product inhibition by glucose-6-phosphate ✓
- C Both enzymes have identical Km but glucokinase is induced by glucagon
- D Glucokinase is a membrane-bound enzyme that requires insulin for catalytic activity
Correct answer: B. Glucokinase has a higher Km for glucose and lacks product inhibition by glucose-6-phosphate
Explanation
Hepatic glucokinase (hexokinase IV) has a high Km for glucose, around 10 mM, so it operates efficiently only at postprandial glucose concentrations, allowing the liver to buffer blood glucose. It is not inhibited by glucose-6-phosphate, unlike hexokinases I to III, which have low Km and strong product inhibition. Glucokinase gene expression is induced by insulin, not glucagon, and the enzyme is cytosolic.
Reference: Lippincott Illustrated Reviews: Biochemistry, 8th ed.
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