The NH2-terminal amino acid sequences (H2N-Ala1-Met36) of highly purified urinary trypsin inhibitor (UTI) and plasma UTI related acid-stable trypsin inhibitor (ASTI) were found to be completely identical. Neither of the inhibitors was not completely inactivated even under acidic conditions with 70% HCOOH at 60°C for 17hr. In particularly, a much higher stability of antiplasmin activity was confirmed in contrast to the antitrypsin activity which gradually decreased.
The reagent 1, 2-cyclohexanedione was used to modify the guanidino group of Arg residues in the UTI molecule. This resulted in complete disappearance of both activities, possibly indicating that UTI and related inhibitors belong to the “Arg-type inhibitor” previously defined by Laskowsky and Sealock. On the other hand, for modification of the ε-amino group of Lys residue in the UTI molecule, 2, 4, 6-trinitrobenzenesulfonic acid was used. The resultant trinitrophenyl derivative of the inhibitor (TNP-UTI) was found to demonstrate approximately 50 times stronger antiplasmin fibrinolysis than the intact inhibitor. Almost no change in antitrypsin or antichymotrypsin activity occurred as a result of the inhibitor modification. The modified inhibitor was also shown to be a potent inhibitor of non-plasmin mediated fibrinolysis with human leukocyte protease.
