Crystallization of the fungal enzyme proteinase K and amino acid composition

Proteinase K is obtained from the fungus Tritirachium album Limber and is named after its keratin-digesting activity. The enzyme, of molecular weight 18,500, is a serine proteinase and hydrolyses proteins at the carboxyl end of hydrophobic amino acids, as does α-chymotrypsin. The amino acid composition of proteinase K was determined by standard methods and the protein was crystallized using an improved dialysis method. The crystals obtained have been characterized by X-ray diffraction methods; the space group is tetragonal, P41212 or P43212 and the cell constants are a = b = 68·3 Å, c = 108·5 Å; two protein molecules are found in one asymmetric unit.