Like all catalysts, enzymes increase the rate of a reaction by lowering its activation energy (E). AS a result, products are formed faster and reactions reach their equilibrium state more rapidly. Most enzymes reaction rates are millions of times faster than those of comparable un-catalyzed reactions and some are so fast that they are diffusion limited. As with all catalysis, enzymes are not consumed by the reactions they catalyze, nor do they alter the equilibrium of these reactions. However, enzymes do differ from most other catalysts in that are highly specific for their substrates. Enzymes are known to catalyze about 4,000 biochemical reactions. A few RNA molecules called ribozymes also display enzyme-like catalysis.