THE FIBRINOLYTIC ACTIVITY OF STREPTOKINASE ACTIVATED

The successful introduction of enzymes for the dissolution of undesirable collections of sanguine-ous, fibrinous, and purulent exudations in local-ized areas of disease in man (1), has stimulated studies on the experimental in vivo dissolution of intravascular blood clots by enzymatic means (24). Activation of plasminogen, the proteolytic enzyme precursor present in plasma, to plasmtin, by streptokinase 2 has received considerable at-tention in these studies (2, 3, 5) not only because of plasminogen's natural occurrence, but because of the special fibrinolytic propensities attributed to SK activated human plasmin (6, 7). Preparations of the human proenzyme prepared by the Kline procedure (8) and activated by strep-tokinase, consistently have fibrinolytic activities of approximately 200,000 units per mg. nitrogen.8 The striking fibrinolytic activity of streptokinase activated human plasmin preparations is very large when compared to their known and measurable proteolytic activity. It seems unusual for an en-zyme which extensively attacks a great variety of protein substrates (9-i 1), and has the same spec-trum of activity as trypsin on synthetic substrates (12), to have such a unique fibrinolytic activity. It is the purpose of this report to present evi-dence that, (a) the fibrinolytic activity of human plasmin preparations is comparable to that of other known proteolytic enzymes, and (b) the extra-ordinary fibrinolytic activity of streptokinase ac-tivated human plasmin, when measured with the conventional bovine clot, is due to the activation of a contaminating bovine plasminogen in the fibri-nogen preparation used in the assay system. Thi