Human Inter-α-Trypsin Inhibitor: Localization of the Kunitz-Type Domains in the N-terminal Part of the Molecule and their Release by a Trypsin-Like Proteinase

Abstract
The N-terminal amino-acid sequence of human ITI has been found to be identical with that of the acid-stable human 30-kDa [kilodalton] inhibitors (HI-30) from urine, serum and those released from inter-.alpha.-trypsin inhibitor by trypsin or chymotrypsin. Serum HI-30 and HI-30 released by trypsin differ from the urinary inhibitor by an additional C-terminal arginine residue. Compared to these 2 inhibitors the inhibitor released by chymotryptic proteolysis is elongated C-terminally by an additional phenylalanine residue. HI-30 is favored as the N-terminus of the inter-.alpha.-trypsin inhibitor and its release from this inhibitor in vivo by cleavage of the Arg123-Phe124 peptide bond by tryspin-like proteinases.