Michaelis-Menten constant (Km) measures enzyme-substrate affinity

Steps:

• Recall that the Michaelis-Menten equation describes enzyme kinetics: v = (Vmax [S]) / (Km + [S]), where Km is the substrate concentration at half Vmax.
• Understand Km as an inverse measure of affinity: lower Km means tighter enzyme-substrate binding.
• Evaluate options: Km compares affinities across enzymes or variants, not changes within one enzyme or other factors.
• Select B, as it directly matches Km's role in comparing enzyme-substrate interactions.

Why B is correct:

• Km is defined as the dissociation constant (Kd) in enzyme kinetics, where lower Km reflects higher affinity for the substrate, allowing comparison between different enzymes.

Why the others are wrong:

• A: Activation energy is lowered by enzymes but measured via Arrhenius plots, not Km.
• C: Km remains constant for a given enzyme regardless of substrate concentration.
• D: Vmax varies with temperature due to enzyme stability, while Km assesses affinity independently.

Final answer: B