Trypsin is an endopeptidase that cuts peptide bonds on the C-terminal side of lysine and arginine residues. It is highly homologous to chymotrypsin and has the same catalytic triad and oxyanion hole. It is activated from the zymogen trypsinogen by cleavage of the peptide bond between residues 15 and 16.

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Enzyme only
Substrate only
Limit to key residues 
 Tetrahedral intermediate
Catalytic functions
 Serine 195
 Histidine 57
 Aspartate 102
 Gly 193 & Ser 195 amide Ns 
The carbonyl O in the oxyanion hole
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Substrate specificity
 Substrate basic side chain
 Aspartate 189
Zymogen activation
 Isoleucine 16 terminal amine
 Aspartate 194