Question

[S]	V
(mmol/L)	(mmol/L/min)
0	0
8.33	13.8
10	16
12.5	19
16.7	23.6
20	26.7
25	30.8
33.3	36.3
40	40
50	44.4
60	48
80	53.4
100	57.1
200	66.7

Consider the following kinetic data for an enzyme. Construct both an M&M and Lineweaver-Burke plots using this data. Estimate the Km and Vmax from both graphs and compare the values. Discuss any differences you see between the numbers you derive from the two different plots.

Answer 1

Michaelis Menten equation is given as -

V = Vmax [S] / KM + [S]

where KM = Michaelis constant that gives us the affinity of the enzyme to the substrate. It is also equal to the substrate concentration when Vmax is half it's value.

Vmax = maximum rate of the reaction.

Plotting [S] vs V (rate) gives us a hyperbola that allows us to calculate KM and Vmax but not accurately. Hence a reciprocal of those values is taken and the equation is converted into a straight line equation and is plotted. We call it the Lineweaver Burke equation. It is given by -  

1/V = (KM / Vmax) . (1/[S]) + (1/Vmax)

Plotting 1/[S] vs 1/V gives us a linear plot. Using the slope and the intercept values we can accurately calculate KM and Vmax values.

You will notice a difference between the values obtained from the two graphs. It's because values of Michaelis Menten have been obtained asymptotically. Lineweaver Burk gives far more accurate values.