STUDIES ON THE INTERACTION OF HUMAN CATIONIC TRYPSIN WITH SERUM PROTEASE INHIBITORS

Abstract

Molecular size distribution of exogenous and endogenous trypsin in serum was investigated using purified trypsin and radioimmunoassay of trypsin developed in our laboratory.
When a small amount of 125I-labelled trypsin was added to normal serum, the 125I-labelled enzyme was partitioned between α2-macroglobulin (α2M) and α1-antitrypsin (α1AT) in a ratio of approximately 70: 30, and increasing amount of added trypsin increased the formation of al AT-trypsin complex. In contrast, 125I-trypsin was more likely to bind to α1AT in pancreatitis serum, even when the amount of exogenous trypsin was small, suggesting α2M had already been occupied by pancreatic proteases in acute pancreatitis. The partition of exogenous trypsin between α2M and α1 AT was affected by the amount and the ratio of α2M and α1 AT in serum.
In normal serum, immunoreactive trypsin existed as trypsinogen. In pancreatitis patients serum, however, it was in part associated with the serum protease inhibitors αl AT and inter-α-antitrypsin, and the remainder existed as trypsinogen but no immunoreactive trypsin was found in the α2M fraction.