[2] Members of the papain family are widespread, found in baculoviruses,[3] eubacteria, yeast, and practically all protozoa, plants and mammals.

[2] The proteins are typically lysosomal or secreted, and proteolytic cleavage of the propeptide is required for enzyme activation, although bleomycin hydrolase is cytosolic in fungi and mammals.

The activation process of these enzymes includes the removal of propeptide regions, which serve a variety of functions in vivo and in vitro.

[5] The papain precursor protein contains 345 amino acid residues,[6] and consists of a signal sequence (1-18), a propeptide (19-133) and the mature peptide (134-345).

[9] Papain prefers to cleave after an arginine or lysine preceded by a hydrophobic unit (Ala, Val, Leu, Ile, Phe, Trp, Tyr) and not followed by a valine.

Meat tenderisers in powder form with papain as an active component are widely sold and the culinary use of papaya peel has featured in research papers.

A ten-minute treatment of small tissue pieces (less than 1 mm3) will allow papain to begin cleaving the extracellular matrix molecules holding the cells together.

The papain-digested antibody is unable to promote agglutination, precipitation, opsonization, and lysis, however, the Fab fragment is still able to bind to and neutralize appropriate antigens, most commonly seen in the use of sheep anti-Crotalid toxin antibody preparations, known as CroFab and in Digibind, a similar sheep antiserum fragment, used to neutralize the cardiac medication digoxin in acute overdose situations.

[18] According to the FDA's statement on the subject, "These unapproved products have put consumers' health in jeopardy, from reports of permanent vision loss with unapproved balanced salt solutions to a serious drop in blood pressure and increased heart rate from the topical papain products," said Janet Woodcock, director for the Center for Drug Evaluation and Research.

Trade names for these products include Accuzyme, Allanfil, Allanzyme, Ethezyme, Gladase, Kovia, Panafil, Pap Urea, and Ziox.

Reports included hypersensitivity (allergic) reactions that lead to hypotension (low blood pressure) and tachycardia (rapid heart rate).

FDA recommended that people with concerns about using topical papain preparations contact their health care provider about discontinuing use.