An enzyme has Km = 2 mM and Vmax = 100 nmol/min. At a substrate concentration of 2 mM, the reaction velocity is:

• A 100 nmol/min
• B 50 nmol/min ✓
• C 75 nmol/min
• D 25 nmol/min

Explanation

By the Michaelis-Menten equation, V = Vmax[S]/(Km + [S]). When [S] equals Km, the equation simplifies to V = Vmax × Km/(Km + Km) = Vmax/2. Therefore, at [S] = Km = 2 mM, the velocity equals Vmax/2 = 50 nmol/min. This relationship defines the Km: it is numerically equal to the substrate concentration at which the reaction proceeds at half its maximal velocity, reflecting the affinity of the enzyme for its substrate.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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