[The inter-alpha-trypsin inhibitor as precursor of the acid-stable proteinase inhibitors in human serum and urine].
A small amount of antitryptic activity is detectable in the supernatant of deproteinized human serum. Preincubation of serum with trypsin causes an increase in acid-stable antitryptic activity. This rise in activity depends on the inter alpha-trypsin inhibitor concentration. The native inhibitor present in normal sera, and in higher concentrations in sera of patients with nephropathies, and the trypsin-liberated inhibitor show immunological cross reaction with antibodies to the serum inter-alpha-trypsin inhibitor. The two inhibitors differ in molecular weight and electrophoretic mobility. The physiological inhibitor (I-34), with a molecular weight of 34 000 and a high carbohydrate content, can be transformed by trypsin into an inhibitor (I-17) with a molecular weight of 17 000. This inhibitor is identical with the inhibitors liberated by trypsin from serum or from purified inter-alpha-trypsin inhibitor. The acid-stable inhibitor from urine is identical with the physiological serum inhibitor. Analogously, this inhibitor is transformed by trypsin into the inhibitor with a molecular weight of 17 000. We conclude that the inter-alpha-trypsin inhibitor is the precursor of both the physiological and the trypsin-liberated inhibitor. By a mechanism as yet unknown, but most likely a limited proteolysis, the secreted inhibitor is liberated from the high molecular weight precursor. In contrast to the monospecific trypsin-inhibiting precursor, the physiological and artificially liberated inhibitors are trypsin/chymotrypsin/plasmin inhibitors.
D006801:Humans; D006863:Hydrogen-Ion Concentration; D007122:Immunoelectrophoresis; D008970:Molecular Weight; D011498:Protein Precursors; D014357:Trypsin; D014361:Trypsin Inhibitors / Q000097:blood* / Q000652:urine; D000515:alpha 1-Antitrypsin / Q000032:analysis
D011498:Protein Precursors; D014361:Trypsin Inhibitors; D000515:alpha 1-Antitrypsin; D014357:Trypsin