What happens to the y-intercept in the presence of an uncompetitive inhibitor?

In a reaction involving an enzyme, uncompetitive inhibition occurs when the inhibitor binds only to the enzyme-substrate complex, preventing it from converting the substrate into product. This type of inhibition leads to a decrease in both the maximum reaction velocity (Vmax) and the apparent Michaelis-Menten constant (Km) for the enzyme.

When examining a Lineweaver-Burk plot, which is a double-reciprocal plot of reaction rate versus substrate concentration, the y-intercept represents 1/Vmax. Since uncompetitive inhibitors lower Vmax without affecting the amount of substrate available to bind, the maximum reaction rate decreases. As a result, 1/Vmax (the y-intercept) increases because Vmax is in the denominator.

Therefore, the presence of an uncompetitive inhibitor directly leads to an increase in the y-intercept of the Lineweaver-Burk plot, confirming that the correct answer is an increase in the y-intercept.