Enzymes serve as catalysts for chemical reactions in the body. A catalyst is a substance that increases the rate of the reaction without being a part of the reaction itself. It accomplishes this by lowering the activation energy of the reaction, which is the amount of energy required for the reaction to do what it does. pH serves as a limiting factor to the effectiveness of enzymes as a catalyst. If there are too many hydrogen ions (H+) present, this would be a lower pH number, indicating excess hydrogen ions are preventing the enzyme's job as a catalyst. The flip side holds true for bases, as well. If the pH is too high, this indicates the presence of too many hydroxide ions (OH-), which is what bases contribute. These would inhibit the enzymes active role as well. So there is an optimal pH, at which the enzyme will perform its task at peak proficiency.