Which equation describes Michaelis-Menten kinetics?

• A. v = (Vmax[S])/(Km + [S])
• B. v = k[S]
• C. v = (Km[S])/(Vmax + [S])
• D. v = Vmax - k[S]

Answer: (A)

Michaelis-Menten kinetics describe how the rate of an enzyme-catalyzed reaction depends on substrate concentration, capturing the saturation effect when enzymes become fully occupied. The standard equation is v = (Vmax [S])/(Km + [S]). Vmax represents the maximum rate when the substrate is abundant and all enzyme sites are occupied, while Km is the substrate concentration at which the rate is half of Vmax, reflecting the enzyme’s affinity for the substrate.

At low substrate levels (S much less than Km), the rate grows roughly linearly with [S], specifically v ≈ (Vmax/Km) [S]. At high substrate levels (S much greater than Km), the rate approaches Vmax and becomes independent of [S], showing the saturation behavior.

Other forms fail to capture this essential feature: a simple linear dependence lacks the plateau as [S] increases, and the alternative expressions misplace Km, leading to incorrect limiting behavior.