Inhibition of trypsin, chymotrypsin, and plasmin by an inhibitor isolated from sheep serum.

A proteolytic enzyme inhibitor has recently been isolated from sheep serum and, by several criteria, viz. electrophoretic, chromatographic, and ultracentrifugal analysis, apparently behaved as a single component (1). Rat skin proteinase A (2) was used as the test enzyme for the purification of the inhibitor. It has now been determined that this inhibitor preparation can also decrease the activity of trypsin, chymotrypsin, and plasmin but is without effect on several other enzymes. This information, in conjunction with a molecular weight determination, permits a more critical comparison of the properties of the inhibitor from sheep serum with the properties of inhibitors isolated by other workers. A preliminary account of some of this work has been reported elsewhere (3).