Studies on Specificity of Streptokinase.

Summary 1. Ability of SK to activate the fibrinolytic system in plasma or euglobulin fractions of various animal species has been studied. 2. Human, cat, dog and rabbit plasminogens were readily activated by SK. Pig, horse and cow plasminogens were much less readily activated. Sheep, guinea pig and goat plasminogens were not activatable by concentrations of SK employed. 3. When SK is able to induce formation of a fibrinolytic system on addition to a given species of plasma or euglobulin fraction, that particular mixture gains ability to activate plasminogen of an animal species not activatable by SK alone. 4. Mixtures of SK and a species of plasminogen in which fibrinolysis or LEEase activity does not occur are incapable of activating plasminogens refractory to SK activation. 5. Addition of plasma from all animal species studied partially inhibits the LEEase activity of a spontaneous plasmin preparation. 6. Possible implications of these findings are briefly discussed.