Trypsin

Trypsin is a serine protease found in the digestive system of many vertebrates, where it hydrolyses proteins.

"Trypsin cleaves peptide chains mainly at the carboxyl side of the amino acids lysine or arginine, except when either is followed by proline. It is used for numerous biotechnological processes. The process is commonly referred to as trypsin proteolysis or trypsinisation, and proteins that have been digested/treated with trypsin are said to have been trypsinized. Trypsin was discovered in 1876 by Wilhelm Kühne."
--https://en.wikipedia.org/wiki/Trypsin

The STL file contains a representation of the protein in cartoon form with catalytic residues represented as spheres. Model based on the Protein Data Bank entry 4I8H:
--http://www.pdb.org/pdb/explore/explore.do?pdbId=4i8h

Model created using VMD:
http://www.ks.uiuc.edu/Research/vmd/