Pepsin is a digestive protease released by the chief cells in the stomach that functions to degrade food proteins into peptides. According to American Heritage Dictionary, pepsin derives from the Greek word pepsis, meaning digestion (peptein: to digest). Pepsin was discovered by Theodor Schwann in 1836. It was the first animal enzyme to be discovered. Precursor Pepsin is expressed as a pro-form zymogen, pepsinogen, whose primary structure has an additional 44 amino acids. In the stomach, chie… (More on Pepsin)