A novel α2-p1asmin inhibitor (α2Pl), chemically and immunologically distinct from any known inhibitors, has recently been isolated and characterized from human plasma (Moroi and Aoki, J. Biol. Chem. 251: 5956, 1976). We have studied the effect of purified α2PI upon various proteases participating in human blood coagulation and kinin generation. At physiological concentrations, (50 μg/ml), α2PI inhibited the clot-promoting and prekal1 ikrein-activating activity of Hageman factor fragments (HFf, MW = 30,000), the amidolytic, kininogen-ase and clot-promoting activities of plasma kallikrein, and the clot-promoting activity of activated plasma thromboplastin antecedent (activated PTA, XIa). For example, activated PTA was inhibited to 50% and 12% of original activity after incubation with α2PI for 10 and 30 min at 37°c respectively. At higher concentrations (200 μg/ml), activatedStuart factor (Xa) was also inhibited. Heparin (1.5 units/ml) did not enhance the inhibitory function of α2PI against HFf, plasma kallikrein or activated PTA. These results suggest that α2PI is an inhibitor of broad specificity that may play an important role in regulation of blood coagulation, fibrinolysis and kinin generation.
Purified human plasma kallikrein aggregates human blood neutrophils.
