Used in the preparation of fish meal and other protein hydrolysates and in the manuf. of cheese as a milk-clotting agent Pepsin is an enzyme that is released by the chief cells in the stomach and that degrades food proteins into peptides. Pepsin was discovered in 1836 by Theodor Schwann who also coined this enzyme's name from the Greek word pepsis, meaning digestion (peptein: to digest). It was the first animal enzyme to be discovered, and, in 1929, it became one of the first enzymes to be crystallized, by John H. Northrop. Pepsin is a digestive protease.