How does substrate concentration affect the rate of an enzyme-controlled reaction?

The relationship between substrate concentration and the rate of an enzyme-controlled reaction is described by Michaelis-Menten kinetics. When the velocity of an enzymatic reaction is plotted against substrate concentration, the resulting curve is typically a hyperbola.1

The effect of substrate concentration on the reaction rate can be summarized as follows:

• Low Substrate Concentration: At low concentrations, the reaction rate is proportional to the amount of substrate present. In this phase, the rate increases as more substrate is added because there are available active sites on the enzyme molecules to bind with the substrate.213
• High Substrate Concentration: As the concentration of substrate increases, the reaction rate approaches a maximum velocity, known as $V_M$. At this point, all available active sites on the enzyme molecules are occupied, and the enzyme is considered saturated.13
• Saturation: Once the enzyme is saturated, the reaction rate becomes independent of further increases in substrate concentration. The rate is then determined solely by the speed at which the active sites can convert the bound substrate into product.23