Human pepsin is an enzyme, which is released by the chief cells in the stomach in the form of zymogen called pepsinogen. This enzyme is responsible for protein degradation to peptides. The name pepsin was coined by Theodor Schwann who also was the first to discover it in 1836. Human pepsin functions as a digestive protease and belongs to the family of aspartate protease. Human pepsin is one of the three main proteolytic enzymes of the digestive system. Pepsin is known for its efficient cleavage functions of the peptide bonds between hydrophobic and aromatic amino acids like tryptophan, tyrosine and phenylalanine. Expression of pepsin occurs from its pro-form zymogen known as pepsinogen. Its structure consists of additional 44 amino acids. HCL in stomach activates zymogen and leads to its unfolding and cleavage forming pepsin. Pepsin is active under acidic environments at the temperatures between 37oC to 42oc.High pH or inhibitor compounds like pepstatin, can lead to pepsin inhibition. 

Pepsin is one of the key cause for damage of mucosa observed during laryngopharyngeal reflux. Exposure to the active pepsin leads to reduced expression of protective proteins, which further leads to laryngeal damage. Presence of pepsin in airway specimens are used as specific markers for laryngopharyngeal reflux. Commercially pepsin is produced by extraction from the glandular layers of the hog stomachs. It has various applications like, in preparation of animal and vegetable protein hydrolysates and its use in beverages and flavouring foods, removal of hair in leather industries, silver recovery from photographic films which are discarded etc. Pepsin is also used for preparation of F(ab’) 2 fragments from the antibodies.