What is papain?
Papain is a protein-cleaving enzyme derived from papaya and certain other plants.
Enzymes are complex molecules produced in living organisms to
catalyze (speed up) chemical reactions within the cell.
(If you have the Chime plugin for viewing three-dimensional
molecular structures, you can see a model of the papain molecule here) 
Why is meat tough?
Muscles have to endure a lot of mechanical stress; they are made of strong
fibers that make them hard to cut, and tough connective tissue holds them
muscle cells contain microscopic fibrils that give
them their structural integrity and allow them to contract.
The fibrils have a complex internal structure bound together by long
protein chains. The connective tissue that holds the muscle together is also
How does papain tenderize meat?
Papain cuts the protein chains in the fibrils and also in the connective tissue,
disrupting the structural integrity of the muscle fiber, and tenderizing the meat.
1. SCOP Structural Classification of Proteins (Cambridge University)
|A database that shows structural and evolutionary relationships for all proteins whose structures are known. Entries include RasMol and Chime 3D models and links to additional databases.|
Author: Fred Senese firstname.lastname@example.org