In an enzyme reaction, there is a hyperbolic relationship between the rate of reaction and the concentration of substrate, explains a University College London website resource. At a low concentration of substrate, there is a steep increase of the reaction rate as the substrate increases. When the enzyme becomes saturated with substrate, the rate of reaction tapers off to a more even rate.
The maximum rate of reaction is reached when the enzyme is saturated with substrate. The affinity between an enzyme and its substrate determines how fast the reaction occurs. This relationship is known as the Michaelis constant, or Km. An enzyme with a high Km has a low affinity for the substrate and requires a higher concentrate of substrate to achieve the maximum rate of reaction.
A much higher concentration of substrate is needed to ensure the enzyme reacts completely throughout the process. The maximum rate of reaction is guaranteed to be reached when there is much more substrate than enzyme. Reactions with high amounts of substrate are called zero order reactions because rates of reaction are independent of substrate concentration.
The substrate is simply a substance that reacts with an enzyme. These reactions and their mathematical plots are used to determine concentrations of various substances in living tissue. One such reaction occurs when lab technicians use glucose oxidase to measure plasma glucose.