This applet demonstrates competitive inhibition of an enzyme acting on a single substrate. Click on the Start button to plot reaction velocity (V) against substrate concentration ([S]) [left hand graph panel] and to show their double reciprocals in a Lineweaver-Burk plot (1/V versus 1/[S]) [right graph panel].
Apparent Vmaxs are equal to the reciprocals of the intercepts on the 1/V axis of the regression lines in the right graph panel. Apparent Kms are equal to the slopes of the regression lines divided by the corresponding intercepts on the 1/V axis of the regression lines in the right graph panel. The curves drawn through the data points in the left graph panel are obtained by substituting apparent Vmaxs and corresponding apparent Kms in the Michaelis-Menten equation:
Colors refer to different inhibitor concentrations (I0 = 0 mM --- BLACK; I1 = 0.1 mM --- RED; I2 = 0.2 mM --- BLUE; I3 = 0.5 mM --- MAGENTA).
Note that with the default values of [S] and V provided, the apparent Vmax values remain fairly constant as [I] increases, and the apparent Km values increase as [I] increases. This shows that the inhibitor, I, is a "competitive" inhibitor. This type of inhibition is distinguished from "noncompetitive" inhibition, which alters only apparent Vmax, and from "uncompetitive" inhibition which alters both apparent Km and apparent Vmax.
Last update: 07/27/2000
Authors: David Rhodes