Kunitz-Type Proteinase Inhibitors Derived by Limited Proteolysis of the Inter-α-Trypsin Inhibitor, VII. Determination of the Amino-Acid Sequence of the Trypsin-Released Inhibitor from Bovine Inter-α-Trypsin Inhibitor

An acid-labile proteinase inhibitor, quite similar to human inter-alpha-trypsin inhibitor, was isolated from bovine serum. An acid-resistant 30-kDa inhibitor, exhibiting properties similar to human HI-30, was also isolated. Upon limited proteolysis of both bovine inhibitors, active 14-kDa domains are released which are identical with respect to molecular mass and acid resistance. The amino-acid sequence determination of these fragments revealed a strong homology to the corresponding human inhibitor HI-14 which is characterized by two covalently linked Kunitz-type domains. The reactive-site residue is leucine in the N-terminal domain (in the human inhibitor methionine) and arginine in the C-terminal domain in both bovine and human inhibitor.