Enzyme Kinetics: Km and Substrate Affinity

Steps:

• Km is the substrate concentration at half maximum velocity (Vmax) in Michaelis-Menten kinetics.
• Lower Km value indicates higher enzyme-substrate affinity, as less substrate is needed to reach half Vmax.
• On the graph, enzyme Q's curve reaches half Vmax at lower [S] than enzyme P's curve.
• Thus, Q has lower Km and higher affinity than P.

Why C is correct:

• Km inversely relates to affinity: lower Km means the enzyme binds substrate more tightly, per Michaelis-Menten equation V = Vmax [S] / (Km + [S]).

Why the others are wrong:

• A: Q's lower Km means higher (not lower) affinity than P.
• B: Q's lower Km means higher (not lower) affinity than P.
• D: Q's lower Km means higher (not lower) affinity than P.

Final answer: C