In molecular biology Proteinase K (also protease K or endopeptidase K) is a broad-spectrum serine protease. The enzyme was discovered in 1974 in extracts of the fungus Engyodontium album (formerly Tritirachium album). Proteinase K is able to digest native keratin (hair), hence, the name "Proteinase K". The predominant site of cleavage is the peptide bond adjacent to the carboxyl group of aliphatic and aromatic amino acids with blocked alpha amino groups. It is commonly used for its broad specificity.