Question

You perform an enzyme experiment and plot the results on a Lineweaver-Burk plot. You know the Vmax is 5 sec/mol, the x-intercept is 2.5 mM^-1, the v0 of the system is 0.2 sec/mol. What is the Km value?

a) 440s^-1

b) 440 s

c) 4.5 s^-1

d) 0.45 s

e) more information is needed

Answer 1

None of the given options are correct.

Km has the units of substrate concentration usually M (molar), mM (millimolar) or uM (micromolar). Here, it should be mM as the x-intercept value is given as mM^-1.

Lineweaver-burk equation is represented as

1/Vo = (Km/Vmax).(1/[S]) + (1/Vmax)

Given values:

Vo = 0.2 sec/mol,

Vmax = 5 sec/mol,

1/[S] = 2.5 mM^-1​​​​​​.

Putting the given values in the Lineweaver-burk equation, we can obtain value of Km:

1/0.2 = [Km (1/5) (2.5)] + (1/5)

5 - 0.2 = Km x 0.2 x 2.5

Km = 4.8/(0.5)

Km = 9.6 mM