How to Calculate Vmax Lineweaver

How to Calculate Vmax Lineweaver
••• Vitaly Vlasov / EyeEm/EyeEm/GettyImages

Enzymes are proteins that work to lower the activation energy in chemical reactions while not being consumed in the reaction. Biologically, enzymes are essential molecules that speed up reactions in metabolic systems. As a result, enzyme kinetics study the reaction rate of enzymes in various chemical settings. Many factors affect the speed of an enzyme. The concentration of a substrate, temperature, inhibitors and pH influence the threshold of an enzyme in a chemical reaction. With the help of linear relationships such as the Lineweaver-Burk plot, you can find the maximum rate of an enzyme.

Ease of Calculating the Vmax in Lineweaver-Burk Plot

Begin by plotting the Michaelis-Menten equation to get a hyperbole curve. Then, use the reciprocal of the Michaelis-Menten equation to obtain a slope-intercept form of the enzyme activity. Next, you will obtain the rate of enzyme activity as 1/Vo = Km/Vmax (1/[S]) + 1/Vmax, where Vo is the initial rate, Km is the dissociation constant between the substrate and the enzyme, Vmax is the maximum rate, and S is the concentration of the substrate.

Since the slope-intercept equation relates the rate to the concentration of the substrate, you can use the typical formula of y = mx + b, where y is the dependent variable, m is the slope, x is the independent variable, and b is the y-intercept. Before specific computer software, you would use graph paper to draw the line. Now, you use typical database software to plot the equation. So, knowing the initial rate, Vo, and the various concentration of the substrate, you can create a straight line. The line plot represents the slope of Km/Vmax and y-intercept of 1/Vmax. Next, use the reciprocal of the y-intercept to calculate the Vmax of the enzyme activity.

Uses for the Lineweaver-Burk Plot

Inhibitors alter the maximum rate of the enzyme activity mainly in two ways: competitively and noncompetitively. A competitive inhibitor binds to the activation site of an enzyme blocking the substrate. In this way, the inhibitor competes with the substrate to bind to the enzyme site. Allowing high concentration of the competitive inhibitor ensures the binding to the site. Hence, the competitive inhibitor changes the dynamics of the enzymatic rate. First, the inhibitor modifies the slope and the x-intercept Km creating a much steeper slope. However, the maximum rate, Vmax, stays the same.

On the other hand, a noncompetitive inhibitor binds at a different site than the activation site of the enzyme and does not compete with the substrate. The inhibitor modifies the structural components of the activation site preventing the substrate or another molecule from binding to the site. This change impacts the affinity of the substrate to the enzyme. Noncompetitive inhibitors change the slope and the y-intercept of the Lineweaver-Burk plot, decreasing the Vmax while increasing the y-intercept with a steeper slope. However, the x-intercept remains the same. While the Lineweaver-Burk plot is useful in many ways, the line plot has limitations. Unfortunately, the plot begins to distort rates at very high or low substrate concentrations, creating extrapolations on the plot.