What does Km represent in the context of enzyme kinetics?

In enzyme kinetics, Km, or the Michaelis constant, represents the substrate concentration at which the reaction velocity is half of Vmax. This means that when the substrate concentration is equal to Km, the rate of the enzyme-catalyzed reaction reaches 50% of its maximum velocity, Vmax. This is a critical parameter because it provides insight into the affinity of the enzyme for the substrate; a lower Km indicates higher affinity, meaning that the enzyme can achieve half-maximum velocity at a lower substrate concentration.

Understanding Km allows biochemists to compare the efficiency of different enzymes or the same enzyme with different substrates, providing valuable information in both basic research and practical applications like drug design or metabolic engineering. The interpretation of Km as the concentration at which V0 equals half of Vmax is fundamental and widely used in enzymology to analyze enzyme behavior in various conditions.