Definitions

papain

papain

[puh-pey-in, -pahy-in]
papain: see papaya.

Papain is a cysteine protease hydrolase enzyme present in papaya (Carica papaya) and mountain papaya (Vasconcellea cundinamarcensis).

Structure

It consists of 212 amino acids stabilised by 3 disulfide bridges. Its 3D structure consists of 2 distinct structural domains with a cleft between them. This cleft contains the active site, which contains a catalytic triad that has been likened to that of chymotrypsin. Its catalytic triad is made up of 3 amino acids - cysteine-25 (from which it gets its classification), histidine-159, and asparagine-158.

Function

The mechanism by which it breaks peptide bonds involves deprotonation of Cys-25 by His-159. Asn-158 helps to orient the imidazole ring of His-159 to allow this deprotonation to take place. Cys-25 then performs a nucleophilic attack on the carbonyl carbon of a peptide backbone. This frees the amino terminal of the peptide, and forms a covalent acyl-enzyme intermediate. The enzyme is then deacylated by a water molecule, and releases the carboxy terminal portion of the peptide. In immunology, papain is known to cleave the Fc (crystallisable) portion of immunoglobulins (antibodies) from the Fab (antigen-binding) portion.

Uses

Its utility is in breaking down the tough meat fibers and has been utilized for thousands of years in its native South America. It is sold as a component in powdered meat tenderizer available in most supermarkets. Papain, in the form of a meat tenderizer such as Adolph's, made into a paste with water, is also a home remedy treatment for jellyfish, bee, yellow jacket (wasps) stings, mosquito bites, and possibly stingray wounds, breaking down the protein toxins in the venom. It is also the main ingredient in Stop Itch and Stop Itch Plus, a DermaTech Laboratories first aid cream popular in Australia.

Papain is used to dissociate cells in the first step of cell culture preparations. A 10-minute treatment of small tissue pieces (less than 1 mm cubed) will allow papain to begin breaking down the extracellular matrix molecules holding the cells together. After 10 minutes, the tissue should be treated with a protease inhibitor solution to stop the protease action (if left untreated papain's activity will lead to complete lysis of the cells). The tissue must then be triturated (passed quickly up and down through a Pasteur pipette) in order to break up the pieces of tissue into a single cell suspension.

It is also used as an ingredient in various enzymatic debriding preparations, notably Accuzyme. These are used in the care of some chronic wounds to clean up dead tissue.

It can also be found as an ingredient in some toothpastes or mints as teeth-whitener. Its whitening effect in toothpastes and mints however is minimal, because the papain is present in low concentrations, and will be quickly diluted by saliva. It would take several months of using the whitening product to have noticeably whiter teeth.

Immunoglobulins

An antibody digested by papain yields three fragments, two 50 kDa Fab fragments and one 50kDa Fc fragment.

The agents are not approved by the FDA, and according to the latest FDA position/policy papers these products are not legally marketed.

Production

Papain is usually produced as a crude, dried material by collecting the latex from the fruit of the papaya tree. The latex is collected after scoring the neck of the fruit where it may either dry on the fruit or drip into a container. This latex is then further dried. It is now classified as a dried, crude material. A purification step is necessary to remove contaminating substances. This purification consists of the solubilization and extraction of the active papain enzyme system through a government-registered process. This purified papain may be supplied as powder or as liquid.

Action by the FDA to restrict marketing of all topical drug products containing papain

On September 23, 2008, the FDA warned companies to stop marketing topical drug products containing papain by November 4, 2008. The FDA said, "No topical drug product containing papain has been approved by the FDA." 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, M.D., director for the Center for Drug Evaluation and Research. In the same FDA announcement, the FDA states the following:

About Unapproved Topical Papain Products: Topical drug ointments containing papain are used to remove dead or contaminated tissue in acute and chronic lesions, such as diabetic ulcers, pressure ulcers, varicose ulcers, and traumatic infected wounds. Trade names for these products include Accuzyme, Allanfil, Allanzyme, Ethezyme, Gladase, Kovia, Panafil, Pap Urea, and Ziox. Other products are marketed under the names of the active ingredients, for instance, papain-urea ointment.

The FDA is taking action today against these products because it has received reports of serious adverse events in patients using products containing papain. Reports include hypersensitivity (allergic) reactions that lead to hypotension (low blood pressure) and tachycardia (rapid heart rate). In addition, patients who are allergic to latex can also be allergic to papaya, the source of papain. Therefore, patients with latex sensitivity may be at increased risk of suffering an adverse reaction to a topical papain drug product.

FDA urges consumers who are using topical drug products containing papain, and who have questions or concerns, to contact their health care provider about discontinuing treatment with these products. There are a number of FDA-approved topical products that have been found safe and effective as wound healing agents and that do not contain papain.

"Removing unapproved topical drug products containing papain and unapproved ophthalmic balanced salt solutions is yet another step forward for patient safety," said Deborah M. Autor, director, Office of Compliance for CDER, FDA.

References

External links

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