A serine protease inhibitor; inhibits enzyme activity of 24 serine proteases including human leukocyte elastase, thrombin, plasmin, Factor Xa, and Factor XIIa in vitro; stimulates caseinolytic activity of bovine pituitary MPC by inducing a conformational change in the MPC that exposes the caseinolytic active site; has been used to functionally characterize the catalytic activities of multiple proteases including rat liver MPC and extracellular lipase,