Trypsin Inhibitor
In order to prevent the action of active trypsin in the pancreas which can be highly damaging, inhibitors such as BPTI and SPINK1 in the pancreas and α1-antitrypsin in the serum are present as part of the defense against its inappropriate activation. Any trypsin prematurely formed from the inactive trypsinogen would be bound by the inhibitor. The protein-protein interaction between trypsin and its inhibitors is one of the tightest found, and trypsin is bound by some of its pancreatic inhibitors essentially irreversibly. In contrast with nearly all known protein assemblies, some complexes of trypsin bound by its inhibitors do not readily dissociate after treatment with 8M urea.
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