Enzyme Kinetics -- Part I
Part VI. Finding the Km and Vmax by the Graphical Solution Method.
To calculate the Km and Vmax, the Michaelis-Menten equation is converted into a linear form by taking the reciprocal of both sides of the equation. This is called the Lineweaver-Burk equation in honor of the first scientists to describe it.
Figure 9. The Lineweaver-Burk equation linearizes the M-M equation by taking the reciprocal of both sides of the equation. This equation then takes on the form of the equation of a line. The y values are 1/Vo, the x values are 1/[S]. The b value in the line equation is the slope and equal to Km/Vmax, while the c value is the y-intercept and equal to 1/Vmax.
The double reciprocal plot is useful for deriving Km and Vmax by plotting kinetic data for an enzyme and you should use it to find the Km and Vmax via graphing for the problem set you got today.
Figure 10. The double reciprocal plot for enzyme kinetic data.
This plot must be used to find Km and Vmax for enzyme kinetic data in this class as shown on the graphic. The y-intercept is the 1/Vmax. The x-intercept, which is found in the 4th quadrant, is -1/Km. Alternatively, the Km value can be found from the slope using the Vmax value found from the y-intercept.
However, there are statistical problems with the Lineweaver-Burk equation and double reciprocal plots, so today in research, one derives Km and Vmax using other methods such as the direct linear plot using a computer program. However, the Lineweaver-Burk equation makes the clearest representation of kinetic data and makes it easy to understand the results, so it is most often used to illustrate the data even when the Km and Vmax are derived by other methods.
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©Wilbur H. Campbell, 1995; wcampbel@mtu.edu