Enzymology

In the name of Allah, the Most Beneficial, the most Merciful.

Uncompetitive inhibitors actually DECREASE the Michaelis-Menten constant. Have you ever wondered why?

According to what I've found from http://www.chm.davidson.edu/erstevens/Lineweaver/Lineweaver.html, the answer is this:

Uncompetitive inhibitors are thought to bind the E-S complex and not the enzyme. As with non-competitive inhibitors, the E-S-I complex cannot form the product. The product can only be formed from the E-S complex (Scheme 4). The effect of an uncompetitive inhibitor is to decrease both Vmax and Km. The drop in Km deserves some comment. Km is a measure of substrate affinity for the enzyme. A lower Km corresponds to a higher affinity. The presence of an uncompetitive inhibitor actually increases the affinity of the enzyme for the substrate. This surprising fact can be understood through the binding equilibrium. Since the inhibitor binds the E-S complex, the inhibitor decreases the concentration of the E-S complex. By Le Chatlier's principle, equilibrium of the enzyme and substrate will shift to form more E-S complex. Therefore, the enzyme demonstrates a higher affinity for the substrate eventhough this higher affinity does not lead to a higher Vmax. In a Lineweaver-Burk plot, uncompetitive inhibitors shift the line higher with a raised y-intercept.

Allah knows best.