Fractionation and characterization of an inhibitor of plasmin found in normal plasma

Abstract

Ultracentrifugation and enzyme kinetic studies with casein (pH stat) and LME assays have demonstrated that the immediate plasma plasmin inhibitor is a high-density protein which acts as a noncompetitive inhibitor of plasmin. The affinity of this inhibitor for plasmin (1.7×107M) is about three to five magnitudes greater than the affinity of casein (9.0×104M) or LME (5.5×101M) for plasmin. This supports the concept that this inhibitor can act effectively under physiologic conditions to protect proteins which are susceptible to digestion by plasmin in vivo.