In competitive inhibition, how does the slope of the graph change?

In competitive inhibition, the primary effect is on the enzyme's affinity for the substrate. This type of inhibition occurs when an inhibitor competes with the substrate for binding to the active site of the enzyme. When analyzing the Michaelis-Menten kinetics in the presence of a competitive inhibitor, we typically refer to the Lineweaver-Burk plot (a double reciprocal plot of 1/V versus 1/[S]).

In this plot, the slope is determined by the ratio of Km (Michaelis constant) to Vmax. In the presence of a competitive inhibitor, the apparent Km increases while Vmax remains unchanged. This results in a change in slope because the slope of the Lineweaver-Burk plot is given by Km/Vmax. Specifically, if Km increases due to the inhibitor, the overall slope of the graph also increases proportionally.

The factor α represents how much the Km is affected by the presence of the inhibitor, which means the slope increases by this factor. Therefore, the decision to choose that the slope increases by a factor of α directly reflects the kinetics of competitive inhibition and illustrates how the inhibition alters the enzyme kinetics.