Hexokinase vs. Glucokinase
HEXOKINASE (I, II & III) vs. GLUCOKINASE (IV)
Tissue distribution
- Hexokinase
- Skeletal muscle (most common example even though it occurs throughout most of the body)
- Glucokinase
- The liver
- The pancreas (its beta cells)
- Less notably, also in select cells of the intestine and brain.
Kinetics (Km and Vmax)
- Hexokinase
- lower Km
- lower Vmax
- at fasting glucose levels, hexokinase is at Vmax
- Glucokinase
- high Km --> spares glucose stores for hexokinase in the brain, muscle and other tissues
- high Vmax
- glucose sensor --> at fasting glucose levels, glucokinase activity varies according to blood glucose concentration
Regulation (allosteric vs hormonal)
- Hexokinase (allosteric regulation)
- allosterically inhibited by glucose-6-phosphate
- Glucokinase (hormonal regulation)
- inhibited by glucagon
- activated by insulin
- inactive when bound to glucokinase regulatory protein (GKRP)