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| - | <applet load='9pap' size='500' frame='true' align='right' caption='Papain Protease I' /> | |
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| - | == Introduction == | + | == '''Adenylate Kinase''' == |
| - | <scene name='Sandbox_33/Papain_protease/1'>Papain</scene>, also known as papaya proteinase I, is a <scene name='Sandbox_33/Cys_residues/1'>cystaine protease enzyme</scene> in papaya (''Carica papaya'') and mountain papaya (''Vasconcellea cundinamarcensis'')<ref>Wikipedia: The Free Encyclopedia http://en.wikipedia.org/wiki/Papain</ref>. Papain is present in the leaves, latex, roots and fruit of the papaya plant <ref>Encyclopedia Britannica: Papain http://www.britannica.com/EBchecked/topic/441803/papain</ref>. The latex of ''Carica papaya'' is a rich source of four cysteine endopeptidases including papain, chymopapain, glycyl endopeptidase, and caricain. The proteins are synthesized as inactive precursors that become active within two minutes of the plant being wounded and the latex expelled. Papain is a minor constituent, but it has been more widely studies because it is more easily purified <ref>Worthington Biochemical Corporation. Worthington Enzyme Manual: Papain http://www.worthington-biochem.com/pap/default.html</ref>.
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| - | == History ==
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| - | Papain was first named in the late nineteenth century by Wurtz and Bouchut who partially purified the product from the sap of papaya. When named, it was simply recognized as proteolytically active constituent in the latex of tropical papaya fruit.
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| - | Throughout the mid 1950's and 1960's, purification and separation techniques improved greatly and pure papain was isolated. The study of papain allowed for great advances in understanding enzymes as proteins. In 1968, papin was the second enzyme to be crystallized and its structure determined by X-ray methods. Papain was the first cysteine protease to have its structure identified.
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| - | In the 1980's, the geometry of the <scene name='Sandbox_33/Cys_residues/4'>active site</scene> was reviewed and the three-dimensional structure was determined to a 1.65 Angstrom resolution. The precursors and inhibitors of papain were extensively studied into the 1990's. Today's research aims to further understand the specificity and structural perturbations brought about by inhibitors, low pH, metal ions, and fluorinated alcohols<ref>Worthington Biochemical Corporation. Worthington Enzyme Manual: Papain http://www.worthington-biochem.com/pap/default.html</ref>.
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| - | == Structure ==
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| - | Papain is a single-chained polypeptide with three <scene name='Sandbox_33/Disulfide_bonds_2/1'>disulfide bridges</scene> and a sulfhydryl group necessary for the activity of the enzyme as well as <scene name='Sandbox_33/Polar_and_nonpolar_residues/1'>polar and non-polar residues</scene>. Papain is a one-chain protein with the following <scene name='Sandbox_33/Secondary_structrues/1'>secondary structures</scene>: five alpha helices (pink) and seven beta sheets (orange). Papain is expressed as an inactive precursor, prepropapain. The papain precursor contains 345 amino acid residues, and consists of a signal sequence, a propeptide, and the mature peptide. The amino acid numbers are based on the mature peptide<ref>Worthington Biochemical Corporation. Worthington Enzyme Manual: Papain http://www.worthington-biochem.com/pap/default.html</ref>. The main chain consists of 212 amino acid residues. The chain is folded into two structural domains with the active site in a groove between the domains containing a catalytic diad. The catalytic diad is made up of the amino acids Cys 25 and His 159<ref>Wikipedia: The Free Encyclopedia http://en.wikipedia.org/wiki/Papain</ref>.
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| - | == Function and Mechanism ==
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| - | The mechanism by which it breaks peptide bonds involves deprotonation of Cys 25 by His 159. Asparagine 175 helps to orient the imidazole ring of His 159 to allow the deprotonation to take place. Cys 25 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<ref>Wikipedia: The Free Encyclopedia http://en.wikipedia.org/wiki/Papain</ref>.
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| - | The formation of the active papain requires several cleavage steps including an initial cleavage of the 18 amino acid preregion (the signal sequence), followed by further cleavage of the glycosylated 114 amino acid proregion. This proregion serves as an intrinsic inhibitor and folding template<ref>Worthington Biochemical Corporation. Worthington Enzyme Manual: Papain http://www.worthington-biochem.com/pap/default.html</ref>.
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| - | Papain is a relatively heat resistant enzyme, with a temperature optimal range of 60-70°C<ref>Wikipedia: The Free Encyclopedia http://en.wikipedia.org/wiki/Papain</ref>.
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| - | == Uses ==
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| - | Papain is used in biochemical research involving the analysis of proteins, in tenderizing meat, in clarifying beer, in removing hair from hides before tanning, and in enzyme-action cleansing agents for soft contact lenses. It is also used in toothpastes and cosmetics and in preparations of various remedies for indigestion, ulcers, fever, and swelling<ref>Encyclopedia Britannica: Papain http://www.britannica.com/EBchecked/topic/441803/papain</ref>. Papain is also used in fluid retention following trauma and surgery. It is used for treating parasitic worms, inflammation of the throat and pharynx, shingles symptoms, ongoing diarrhea, runny nose, and psoriasis. Papain is also used along with conventional treatments for tumors, to treat wounds and sores<ref>WebMed Better information. Better health. Find a Vitamin or Supplement: Papain http://www.webmd.com/vitamins-supplements/ingredientmono-69-PAPAIN.aspx?activeIngredientId=69&activeIngredientName=PAPAIN</ref>.
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| - | == Extraction ==
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| - | The amount and activity of papain isolated from the different parts of the papaya plant vary depending on the age of the tree and whether it is male or female. Higher quantities of crude papain may be extracted from female trees compared with male trees and from older fruits compared with younger fruits. However, papain extracted from young papaya fruit produced by female trees typically is more active than that extracted from old fruit produced by male or hermaphrodite plants<ref>Encyclopedia Britannica: Papain http://www.britannica.com/EBchecked/topic/441803/papain</ref>.
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| - | == Allergies ==
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| - | Papain can trigger allergic reactions in susceptible individuals. Skin reactions may occur following contact with fresh latex from papaya; hypersensitivity reactions may be especially pronounced in persons allergic to latex<ref>Encyclopedia Britannica: Papain http://www.britannica.com/EBchecked/topic/441803/papain</ref>. Taking papain by mouth during pregnancy is possible unsafe. There is a concern that it might cause birth defects or miscarriage. Papain might increase the risk of bleeding in people with clotting disorders<ref>WebMed Better information. Better health. Find a Vitamin or Supplement: Papain http://www.webmd.com/vitamins-supplements/ingredientmono-69-PAPAIN.aspx?activeIngredientId=69&activeIngredientName=PAPAIN</ref>.
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| - | == References ==
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| - | <references/>
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