Hexokinase shows a sigmoidal rise in activity above 10 mM glucose, is induced by insulin, and is inhibited by fructose 6 phosphate. These properties belong to which enzyme?
- A Hexokinase I expressed in brain
- B Hexokinase IV (glucokinase) of liver ✓
- C Phosphofructokinase 1 of muscle
- D Pyruvate kinase of erythrocytes
Correct answer: B. Hexokinase IV (glucokinase) of liver
Explanation
These features describe hepatic glucokinase (hexokinase IV). Its high Km for glucose (about 10 mM versus 0.05 mM for other hexokinases) makes it act as a glucose sensor that handles large postprandial loads. It lacks product inhibition by glucose 6 phosphate but is allosterically inhibited by fructose 6 phosphate via the GKRP regulatory protein, and its gene is upregulated by insulin. Brain hexokinase I has low Km and strong inhibition by glucose 6 phosphate.
Reference: Lippincott Illustrated Reviews: Biochemistry, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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