Low Km Means High Enzyme Affinity for Substrate

Steps:

• Km is the substrate concentration [S] where reaction velocity is half Vmax.
• Low Km value means Vmax is reached at lower [S].
• This indicates high enzyme-substrate affinity, as enzyme binds substrate effectively even at low concentrations.
• Consequently, the reaction approaches maximum rate faster as [S] increases.

Why C is correct:

• Low Km reflects high affinity (from Michaelis-Menten equation: Km = (k_off + k_cat)/k_on; lower Km means stronger binding), allowing quicker progression to Vmax.

Why the others are wrong:

• A: Low Km means high, not low, affinity.
• B: Affinity is high, not low, for low Km.
• D: High affinity speeds, not slows, approach to maximum rate.

Final answer: C