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 V_{max}s are equal to the reciprocals of the intercepts on the 1/V axis of the regression lines in the right graph panel. Apparent K_{m}s 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 V_{max}s and corresponding apparent K_{m}s 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 V_{max} values remain fairly constant as [I] increases, and the apparent K_{m} 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 V_{max}, and from "uncompetitive" inhibition which alters both apparent K_{m} and apparent V_{max}.

Applet code. Last update: 07/27/2000 Authors: David Rhodes