Papain has been used for hundreds of years in the Far East for a variety of diseases and indications. It has been extracted in the pure crystalline form and its structure and mechanism of action have been studied extensively. Papain is composed of 17 different amino acids; these contribute a total number of 185 to the composition of the papain molecule, which has a molecular weight of 20,900. One Warner-Chilcott unit is that quantity of proteolytic enzymes extracted from Carica papaya which, under the conditions specified in the method of assay, will clot 2.64μl of milk substrate in two minutes at 40 C.
During the past five or six years that orally administered enzymes have been available for general use, there has been some controversy regarding mechanism of action and efficacy. Because of the size of the molecule, there has been a reluctance to believe that it can be absorbed
Lund MH, Royer RR. Carica papaya in Head and Neck Surgery. Arch Surg. 1969;98(2):180-182. doi:10.1001/archsurg.1969.01340080072013