Low Km signifies high enzyme-substrate affinity and saturation at low substrate levels

Steps:

• Km is the substrate concentration [S] at half maximum velocity (Vmax) in Michaelis-Menten kinetics.
• A low Km value indicates the enzyme binds substrate tightly, showing high affinity.
• High affinity means the enzyme reaches Vmax at a relatively low [S], as saturation occurs sooner.
• Thus, low Km pairs high affinity with low [S] needed for maximum reaction rate.

Why B is correct:

• Km = [S] at ½ Vmax; low Km directly means high affinity (tight binding) and low [S] to achieve Vmax per the hyperbolic curve.

Why the others are wrong:

• A: High affinity but high [S] for Vmax contradicts low Km's implication of quick saturation.
• C: Low affinity requires high Km and high [S] for Vmax, opposite of low Km.
• D: Low affinity pairs with high Km and high [S], not low [S].

Final answer: B