<P> Pepsin's proenzyme, pepsinogen, is released by the chief cells in the stomach wall, and upon mixing with the hydrochloric acid of the gastric juice, pepsinogen activates to become pepsin . Pepsin is an aspartic protease, using a catalytic aspartate in its active site . </P> <P> Pepsin was one of the first enzymes to be discovered . It was discovered in 1836 by Theodor Schwann . Schwann coined its name from the Greek word πέψις pepsis, meaning "digestion" (from πέπτειν peptein "to digest"). Scientists around this time began discovering many biochemical compounds that play a significant role in biological processes, and pepsin was one of them . An acidic substance that was able to convert nitrogen - based foods into water - soluble material was determined to be pepsin . </P> <P> In 1928, it became one of the first enzymes to be crystallized when John H. Northrop crystallized it using dialysis, filtration, and cooling . </P> <P> Pepsin is expressed as a zymogen called pepsinogen, whose primary structure has an additional 44 amino acids . </P>

The stomach produces pepsin which is a protease to digest