Final answer:
A small KM value in an enzyme-catalyzed reaction signifies very tight binding between the enzyme and the substrate, implying high enzyme efficiency and affinity.
Step-by-step explanation:
In an enzyme-catalyzed reaction, a small value of KM indicates that a substrate binds to the enzyme very tightly. The Michaelis constant (KM) is inversely related to the affinity between the enzyme and the substrate; hence, a low KM implies a high affinity, meaning the enzyme can bind the substrate efficiently even at low substrate concentrations. This high affinity translates to better enzyme efficiency either due to increased catalysis (higher kcat) or better binding (lower KM), or both.
To recapitulate, the two most important kinetic properties of an enzyme are how quickly it becomes saturated with a particular substrate, which is related to the KM for the reaction, and the maximum rate of the catalyzed reaction, described by the Vmax for the reaction.