In non-competitive inhibition, where is the pivot point located on the graph?

In non-competitive inhibition, the kinetics of enzyme activity can be represented through a Lineweaver-Burk plot (double reciprocal plot). The characteristic feature of non-competitive inhibition is that the inhibitor binds to an enzyme regardless of whether the substrate is bound. This leads to a decrease in the maximum reaction rate (Vmax) while the affinity of the enzyme for the substrate, represented by the Michaelis constant (Km), remains unchanged.

On a Lineweaver-Burk plot, which plots 1/V0 (the inverse of the initial velocity) on the y-axis versus 1/[S] (the inverse of the substrate concentration) on the x-axis, the y-intercept indicates the value of 1/Vmax. Since non-competitive inhibitors decrease Vmax without affecting Km, the pivot point—where the slope of the Lineweaver-Burk plot changes due to the inhibition—is not dependent on changing the x-intercept (which relates to Km). Instead, the alteration primarily affects the y-axis, where we see a shift that represents the decreased Vmax.

Therefore, identifying the pivot point on the y-axis aligns with the understanding that non-competitive inhibition primarily impacts the maximum rate of the enzymatic reaction while keeping the enzyme's affinity