Enzymes are complex protein-based catalyst living cells that cause temperature-sensitive biochemical reactions involved in every stage of metabolism. It is believed that about 1000 exist in mammals. An example is ptyalin, a component of saliva that splits starch to begin the digestive process. Other digestive enzymes are amylases, pepsins, lipase, trypsin, chymotrypsin, carboxypeptidase, enteropeptidase, maltase, lactase, sucrase, and nucleosidases. Some enzymes require helpers, known as coenzymes, in order to function. Proteins are principally digested in the stomach with hydrochloric acid and pepsinogen combined, forming a more powerful enzyme called pepsin.
