Mutation Impacts on Enzyme Kinetics

Steps:

• Statement 1: Mutation alters enzyme structure, potentially increasing inhibitor affinity and forming enzyme-inhibitor complex more easily, reducing available enzyme and reaction rate.
• Statement 2: Active site shape change eliminating complementarity prevents substrate binding entirely, implying zero rate rather than a decrease.
• Statement 3: Mutation impairs transition state stabilization, raising activation energy and slowing reaction rate per the Arrhenius equation (rate ∝ e^{-Ea/RT}).
• Select option with valid explanations (1 and 3) for decreased but ongoing catalysis.

Why C is correct:

• Combines increased inhibition (reducing effective [E]) and higher Ea (lowering k_cat via transition state theory), both yielding partial rate reduction without total inactivation.

Why the others are wrong:

• A includes 2, implying complete activity loss inconsistent with "decrease."
• B excludes 3, ignoring how mutations elevate Ea to slow catalysis.
• D excludes 1, overlooking structural changes enhancing inhibitor binding.

Final answer: C