What does a lower value of Km indicate in enzyme kinetics?

A lower value of Km in enzyme kinetics indicates a tighter binding between the enzyme and its substrate. Km, or the Michaelis constant, reflects the concentration of substrate at which the reaction rate is half of its maximum velocity (Vmax). When the Km is low, it implies that only a small amount of substrate is needed to reach half of Vmax, suggesting that the enzyme has a high affinity for the substrate. This strong affinity means that the enzyme is more efficient at binding and converting the substrate into product.

In terms of practical implications, a tighter binding allows the enzyme to be effective at lower concentrations of substrate, enhancing the overall catalytic efficiency. This characteristic is important in biochemical pathways where swift reaction rates are crucial for cellular function. It's important to note that a low Km does not demonstrate how much product is formed, nor does it refer to enzyme concentration, but specifically to the interaction strength between an enzyme and its substrate.