Final answer:
The reaction velocity reaches a maximum at a high substrate concentration due to enzyme saturation where all active sites are occupied, preventing further increase in reaction rate. The Vmax represents the maximum rate and Km is the substrate concentration at which the reaction rate is half of Vmax.
Step-by-step explanation:
The reaction velocity eventually reaches a maximum when the substrate concentration is raised due to enzyme saturation. Initially, as the substrate concentration increases, so does the reaction rate because more substrate molecules are available to bind with enzyme molecules. However, there is a point where all the enzyme's active sites are occupied, and this is called saturation. When saturation is reached, increasing the substrate concentration further will not increase the reaction rate because no additional enzyme molecules are available to bind with the excess substrate.
At maximum velocity or Vmax, all enzyme active sites are filled with the substrate. The reaction rate at this point only depends on the speed at which the substrate turns into product and is released, allowing a new substrate molecule to bind. The Michaelis-Menten constant, or Km, is the substrate concentration at which the reaction rate reaches half of Vmax. This constant helps to describe the efficiency of the enzyme in catalyzing the reaction.