"In vivo" and "in vitro" inhibition of human pancreatic chymotrypsin A by serum inhibitors.

The interaction of human pancreatic chymotrypsin A with serum inhibitors was assessed by enzyme immunoassay, enzymatic activity and inhibitory capacity measurements and electrophoretic analyses. In normal serum, chymotrypsin A was detected in four forms: one form (Mr approximately equal to 25,000) which might be chymotrypsinogen A and three forms complexed to the main inhibitors present in serum, alpha 2-macroglobulin (alpha 2-M), alpha 1-proteinase inhibitor (alpha 1-PI) and alpha 1-antichymotrypsin (alpha 1-Achy). As chymotrypsin A remains to 90% active when bound to alpha 2-M, the chymotrypsin A/alpha 2-M complex was quantified by an enzymatic assay. The kinetic parameters of the interaction of chymotrypsin A with alpha 1-PI and alpha 1-Achy were determined. Using these data the partition of chymotrypsin A between the different inhibitors in serum was calculated. In acute pancreatitis, the chymotrypsin A plasma level follows the progression of the disease and in this case as well as in normal serum alpha 1-PI is the major antagonist of chymotrypsin A.