Which statement about hepatic glucokinase distinguishes it most clearly from hexokinase found in skeletal muscle?
- A It has a lower Km for glucose and is inhibited strongly by glucose-6-phosphate
- B It has a higher Km for glucose, shows sigmoidal kinetics, and is induced by insulin ✓
- C It operates near saturation at fasting blood glucose concentrations
- D It transfers phosphate to C-6 of glucose using NAD+ as cosubstrate
Correct answer: B. It has a higher Km for glucose, shows sigmoidal kinetics, and is induced by insulin
Explanation
Glucokinase (hexokinase IV) has a high Km for glucose, around 10 mmol/L, displays sigmoidal rather than Michaelis-Menten kinetics due to cooperativity, is not inhibited by glucose-6-phosphate, and is transcriptionally induced by insulin after carbohydrate meals. This suits its portal-hepatic role of clearing large postprandial glucose loads. Its high Km means it is far from saturated at fasting glucose levels, unlike muscle hexokinase.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
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