Enzymes are proteins that act as catalysts to increase the rate of biochemical reactions. They do this by lowering the activation energy of reactions. Enzymes have an active site that specifically binds to substrates, and only the correct substrate that fits into this pocket will be affected by the enzyme. Enzymes can be regulated by competitive inhibitors that bind to the active site or allosteric inhibitors and activators that bind elsewhere and induce a shape change that prevents or allows substrate binding.