A decrease in the activation energy increases the rate of the reaction. Enzymes help to speed up reactions that have high activation energies, and therefore occur very slowly or do not occur at all. When the activation energy for a reaction is lowered a larger portion of the reactant molecules have a sufficient amount of energy needed to convert into products. Catalase is a very efficient enzyme; it has one of the highest turnover numbers. For example, catalase can process approximately 5 million hydrogen peroxide molecules per second.