What is the relationship between the Km of an enzyme and its affinity for substrate?

The Km (Michaelis constant) of an enzyme is an important parameter in enzymology. It is the substrate concentration at which the reaction rate is half of its maximum (Vmax).

The relationship between Km and the enzyme's affinity for its substrate is inversely proportional. This means that a lower Km value indicates a higher affinity for the substrate, because it takes a lower concentration of substrate to reach half of the maximum reaction rate. Conversely, a higher Km value indicates a lower affinity for the substrate, because it requires a higher concentration of substrate to reach half of the maximum reaction rate.

In other words, if an enzyme has a high affinity for a substrate, it can bind to it even when the substrate concentration is low, resulting in a low Km value. On the other hand, if an enzyme has a low affinity for a substrate, it needs a high concentration of the substrate to bind to it, resulting in a high Km value.

Therefore, the Km of an enzyme can give us valuable information about how effectively an enzyme can bind to its substrate under different substrate concentrations.