Hexokinase !

Hexokinase opens glycolysis: it puts a phosphate on glucose and traps it inside the cell.

Updated 2026-10-31

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Key facts

Glucose + ATP → glucose 6-phosphate + ADP, with Mg²⁺; irreversible.
Hexokinases I–III: high affinity (low Km, ~0.1 mM), slowed by glucose 6-phosphate; at work in nearly every tissue.
Glucokinase (liver, β cell): low affinity (Km ~8–10 mM), not slowed by G6P; acts as a glucose sensor.
When glucose binds, the enzyme closes like a hand (induced fit) and keeps water out.

Glucose 6-phosphate inhibits hexokinase I–III.
Insulin induces glucokinase; the GKRP protein keeps it in the nucleus while fasting and releases it when glucose rises.

Mutations switching off one copy of glucokinase cause MODY 2: mild, stable hyperglycemia that usually needs no treatment.
Activating glucokinase mutations cause hyperinsulinemic hypoglycemia.
Red-cell hexokinase deficiency causes hemolytic anemia and lowers 2,3-BPG.

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Why does glucokinase work as a glucose sensor?

Its Km is high (near blood glucose) and its product doesn't inhibit it: its rate follows blood glucose.

What does losing one copy of GCK cause?

MODY 2: mild, stable hyperglycemia from birth.

Why does FDG-PET light up tumours?

Hexokinase phosphorylates FDG, which goes no further in glycolysis and is trapped in glucose-hungry cells.

Educational information, not medical advice. For any symptom, see a health professional.

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Representative model, for educational purposes only.