Kunitz-Type Proteinase Inhibitors Derived by Limited Proteolysis of the Inter-α-Trypsin Inhibitor, X. The Amino-Acid Sequences of the Trypsin-Released Inhibitors from Horse and Pig Inter-α-Trypsin Inhibitors

The amino-acid sequences of the acid-resistant inhibitors released from horse and pig inter-alpha-trypsin inhibitor (ITI) by tryptic proteolysis were determined. They are composed of two covalently linked Kunitz-type domains. In both cases the reactive site of their C-terminal antitryptic domains is occupied by arginine as in the homologous human and bovine inhibitors. The reactive site of their N-terminal domain exhibits only a weak interaction with polymorphonuclear granulocytic elastase and is occupied by leucine as in the strong elastase inhibitor released from bovine ITI. The differences between inhibitory activities of the ITI-derived inhibitors from horse, pig, and cattle are discussed on the basis of sequence differences in position P'2.