Kunitz-type proteinase inhibitors derived by limited proteolysis of the inter-alpha-trypsin inhibitor, IX. Isolation and characterization of the inhibitory parts of inter-alpha-trypsin inhibitors from several mammalian sera.

The inhibitory parts of inter-alpha-trypsin inhibitor-like proteins from several mammalian sera (sheep, goat, horse, donkey, pig, rabbit, rat and dog) were released by limited proteolysis with trypsin and were isolated by reversible binding to immobilized trypsin. The inhibitors are very similar with respect to their stability in acids, molecular masses and amino-acid compositions. They are different, however, in their inhibitory properties. In view of the known covalent structures of the inhibitory parts of the human and bovine inhibitors, homologous covalent structures consisting of two tandem Kunitz-type domains are suggested also for the isolated inhibitors. Bovine trypsin, bovine chymotrypsin and porcine plasmin are inhibited by all investigated inhibitors, most likely via their C-terminal domain. The inhibitors from horse, donkey, rabbit, rat and dog serum interact also with elastase from human polymorphonuclear granulocytes, those from sheep, goat and pig serum inhibit in addition porcine pancreatic elastase and bovine chymotrypsin via their N-terminal Kunitz-type domain. It is supposed that the amino-acid residue in position P1 of the N-terminal Kunitz-type domain is responsible for the characteristic inhibitory properties of each inhibitor.