Enzyme activity refers to the rate at which an enzyme catalyzes the conversion of a substrate into a product. This activity increases when a substrate molecule binds to the enzyme's active site, which is the specific region where the substrate interacts with the enzyme. However, enzyme saturation occurs when there are more substrate molecules than available active sites on the enzyme. Since enzymes are finite in number, there is a limit to how many substrates can bind at any given time.

As substrate concentration increases, more substrate molecules occupy the active sites until all are filled. At this point, the enzyme is said to be saturated, meaning that even though there are still substrate molecules present, they cannot bind to the enzyme because all active sites are occupied. This saturation point is crucial for understanding enzyme kinetics, as it indicates that the reaction rate has reached its maximum under the given conditions.

Several factors can influence enzyme activity, including temperature, pH, substrate concentration, and the presence of inhibitors or activators. Each of these factors can alter the shape and function of the enzyme, thereby affecting its ability to catalyze reactions efficiently.