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, soft-stemmed tree (Carica papaya) of tropical America resembling a palm with a crown of palmately lobed leaves. It is cultivated for its melonlike yellow fruits eaten raw or cooked and, more recently, for the juice which has become a commercial item.
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a proteolytic vegetable enzyme of the hydrolase class. Papain exhibits a wide range of substrate specificities, catalyzing the hydrolysis of peptide bonds in proteins and peptides and the hydrolysis of amides, ethers, and thioesters. Crystalline papain is obtained from the sap of the papaya tree (Carica papaya), where it is present in large quantities. The papain molecule is made up of a single polypeptide chain that consists of 212 amino-acid residues. Its molecular weight is 20,900, and the amino-acid sequence has been fully worked out. The active site of papain contains a sulfhydryl group (—SH) and a histidine radical. Papain is used to process leather, tenderize meat, and lighten the color of beverages.
REFERENCESKretovich, V. L. Osnovy biokhimii rastenii, 5th ed. Moscow, 1971.
Mosolov, V. V. Proteoliticheskie fermenty. Moscow, 1971.