Km Reflects Enzyme-Substrate Affinity

Steps:

• Michaelis-Menten equation: v = Vmax [S] / (Km + [S]), where Km is [S] at half Vmax.
• Low Km means enzyme saturates (reaches Vmax) at lower [S], showing strong binding.
• High Km requires higher [S] for saturation, indicating weak binding.
• Vmax is max rate when enzyme is fully saturated, unaffected by Km.

Why D is correct:

• Low Km signifies high affinity, as enzyme binds substrate effectively at low concentrations per the definition of Km as half-saturation point.

Why the others are wrong:

• A: High Km means low affinity, so Vmax requires high [S], not low.
• B: High Km indicates low affinity, opposite of the statement.
• C: All enzymes reach Vmax at high [S], but low Km specifically excels at low [S], making this nondistinctive.

Final answer: D