In the Michaelis-Menten equation, Km represents what?

Km, or the Michaelis constant, is a key parameter in the Michaelis-Menten equation that describes enzyme kinetics. Specifically, Km represents the substrate concentration at which the rate of the reaction is half of the maximum velocity (Vmax) of the enzyme. This concentration gives insight into the affinity of the enzyme for its substrate; a lower Km indicates a higher affinity, meaning that the enzyme reaches half of its maximum velocity at a lower concentration of substrate.

This characteristic makes Km particularly useful for comparing the efficiencies of different enzymes or different substrates for a specific enzyme. Understanding Km assists in determining how an enzyme behaves under different substrate concentrations which is crucial for elucidating its role in metabolic pathways and for practical applications like drug design and enzyme engineering.