Serum Inhibition of Plasmin

In the various studies tha t have been done on the inhibition of proteolytic enzymes by serum, no distinction has been made in the inhibition of different enzymes. I t has generally been assumed that all proteolytic inhibition is caused by the same substance in serum and that this substance is occasionally increased in association with disease. There has been no evidence for the existence of separate proteolytic inhibitors. There have been several at tempts to isolate the material in serum responsible for the inhibition of proteolytic enzymes (1, 2), but no inhibitory material has yet been obtained in pure form. The chemical characteristics of the inhibitory material in serum are not well known. The data t0 be presented indicate tha t more than one antiproteolytic factor can be detected in serum and that these factors act selectively on the enzymes plasmin, trypsin, and chymotrypsin. For the sake of convenience, the factor in serum which inhibits an enzyme will be referred to as the enzyme inhibitor (e.g., plasm{n inhibitor, trypsin inhibitor), although each inhibitor m a y b e composed of several substances or groups of substances.