The Interaction of Streptokinase with Human, Cat, Dog, and Rabbit Plasminogens: THE FRAGMENTATION OF STREPTOKINASE IN THE EQUIMOLAR PLASMINOGEN-STREPTOKINASE COMPLEXES

Abstract Highly purified human (Lys-forms), cat, dog, and rabbit plasminogens showed significantly different sensitivities to activation by highly purified streptokinase. The most sensitive plasminogen is the human zymogen, followed by the cat, dog, and rabbit zymogens, respectively. These human, cat, dog, and rabbit zymogens reacted with streptokinase to form homogeneous equimolar plasminogen-streptokinase complexes. The electrophoretic mobilities of the human and cat complexes on cellulose acetate were different from their respective zymogens, but the electrophoretic mobilities of the dog and rabbit complexes were similar to their respective zymogens. The human, cat, and dog complexes showed different mobilities from their respective zymogens in acrylamide gel electrophoretic systems and appeared to show multiple electrophoretic forms. With these species, all of the multiple isoelectric forms of the zymogens reacted with streptokinase. Analyses of the human (Glu- and Lys-forms), cat, dog, and rabbit equimolar plasminogen-streptokinase complexes, incubated for various time intervals, in an acrylamide gel-dodecyl sulfate-urea electrophoretic system, showed the gradual conversion, or transformation, of the plasminogen-streptokinase complexes into plasmin-streptokinase complexes. These transformations occurred at different rates in each of the mammalian plasminogen-streptokinase complexes. This acrylamide gel system also permitted a comparison between the plasmin-derived carboxymethyl heavy (A) and carboxymethyl light (B) chains produced from these mammalian zymogens by two different methods of activation, namely with equal molar ratios of streptokinase to zymogen and with low molar ratios of urokinase to zymogen (1:1000). The carboxymethyl heavy (A* and A') chains produced by streptokinase activation of the human (Glu-forms), cat, and rabbit plasminogens in the complex appeared to have higher molecular weights than the major carboxymethyl heavy (A and A1) chains derived from each of these zymogens by urokinase activation; the human (Lys-forms) and dog carboxymethyl heavy (A and A') chains appeared to be similar in both activation systems. The carboxymethyl heavy (A* and A') chains of the human (Glu- and Lys-forms), cat, dog, and rabbit plasmins found in the complexes were similar but not identical with each other in molecular weight. The plasmin-derived carboxymethyl light (B') chains produced by streptokinase activation of the human (Glu- and Lys-forms), cat, dog, and rabbit plasminogens in the complex appeared to have molecular weights similar to the carboxymethyl light (B) chains derived from each of these plasminogens by urokinase activation. But, the plasmin-derived carboxymethyl light (B') chains of the four species obtained from the equimolar complexes appeared to have somewhat different molecular weights. Streptokinase fragmentation within the complexes occurs within a few seconds after the complexes are formed, and intact streptokinase disappears after several minutes of incubation. Four major streptokinase fragments (SK1, SK2, SK3, and SK4), having molecular weights between 47,600 and 25,700, are produced in each of the equimolar human (Glu- and Lys-forms), cat, dog, and rabbit complexes. They appear to be the same fragments in each of the mammalian plasminogen-streptokinase and plasmin-streptokinase complexes; each of the complexes contains varying amounts of streptokinase fragments, SK1, SK2, SK3, and SK4. But, the rate of degradation of streptokinase into these major fragments differed with each species. Plasmin and streptokinase moieties prepared by dissociation of an equimolar plasminogen (Lys-forms)-streptokinase complex at pH 3.0 (Summaria, L., Robbins, K. C., and Barlow, G. H. (1971) J. Biol. Chem. 246, 2136–2142) were also analyzed in the acrylamide gel-dodecyl sulfateurea electrophoretic system. The isolated plasmin moiety gave carboxymethyl heavy and carboxymethyl light chains, both of which were of lower molecular weight than the plasmin-derived carboxymethyl heavy (A) and carboxymethyl light (B) chains produced by urokinase activation. The isolated streptokinase moiety contains approximately equal amounts of streptokinase fragments SK2 and SK4, and a third smaller fragment.