What effect does uncompetitive inhibition have on Km and Vmax?

Uncompetitive inhibition occurs when an inhibitor binds to the enzyme-substrate complex, preventing the complex from releasing products. This type of inhibition affects both the maximum velocity (Vmax) of the reaction and the Michaelis constant (Km).

In uncompetitive inhibition, although the substrate can bind to the enzyme, the presence of the inhibitor stabilizes the enzyme-substrate complex and makes it less likely to convert to product. Consequently, the effective concentration of available enzyme is reduced, leading to a decrease in Vmax. Since the inhibitor also binds to the enzyme-substrate complex, it alters how effectively the enzyme can process the substrate, which typically causes Km to decrease, as it effectively increases the affinity of the enzyme for the substrate – the enzyme is more "inhibited," thus appearing to require less substrate concentration to reach its maximum rate.

In summary, uncompetitive inhibition leads to both Km and Vmax decreasing. This is a characteristic effect of this inhibition type, distinguishing it from other forms of enzyme inhibition.