In red blood cells, hexokinase has a Michaelis constant KM, of approximately 50 μM, and the substrate concentration, [S], is equal to the blood glucose concentration.

Question

In red blood cells, hexokinase has a Michaelis constant KM, of approximately 50 μM, and the substrate concentration, [S], is equal to the blood glucose concentration. Calculate the blood glucose concentration that would yield a hexokinase reaction velocity, 𝑉0, equal to 90% of its maximum reaction velocity, 𝑉max. 

Answer 1

Michaelis Menten equation: v = Vm[S] / Km + [S]

v = velocity = 0.9Vm

Vm = maximum velocity

Km = Michaelis constant = 50 uM

[S] = concentration of substrate = ?

0.9Vm = Vm[S] / 50 + [S]

Vm[S] = 45Vm + 0.9Vm[S]

0.1Vm[S] = 45Vm

[S] = 450 uM