What effect does non-competitive inhibition have on the y-intercept of the Lineweaver-Burk plot?

Non-competitive inhibition has a distinct impact on enzyme kinetics that is reflected in the Lineweaver-Burk plot, which is a double-reciprocal transformation of the Michaelis-Menten equation. In this plot, the y-intercept corresponds to the value of (1/V_{max}), where (V_{max}) is the maximum rate of the reaction.

In the presence of a non-competitive inhibitor, the maximum reaction velocity ((V_{max})) decreases because the inhibitor binds to the enzyme regardless of whether the substrate is present, thus reducing the effective concentration of the enzyme available for catalysis. However, because the inhibitor does not prevent the substrate from binding to the enzyme, the Michaelis constant ((K_m)) remains unchanged.

Since (V_{max}) decreases when there is a non-competitive inhibitor, the value of (1/V_{max}) increases. On the Lineweaver-Burk plot, this change is manifested as a shift of the y-intercept upward. Therefore, an increase in the y-intercept indicates that the apparent (V_{max}) has dropped, leading to a higher value for (1/V_{max}).

This behavior is characteristic of non-competitive