Why do uncompetitive inhibitors cause a proportional decrease in both apparent Km and Vmax?

• A. They compete with the substrate, reducing its binding to the enzyme.
• B. They bind to the free enzyme, increasing substrate affinity and reaction rate.
• C. They bind to the enzyme-substrate complex, reducing its concentration and shifting equilibrium.
• D. They increase the concentration of enzyme-substrate complex, enhancing reaction rate.

Answer: (C)