THE Jomwar. OF BIOLOGICAL CHEMISTRY

Bovine plasminogen activator was isolated from a mixture of streptokinase and human plasminogen. The method of preparation was based on the difference in solubility between the activator and its precursors. The activator can be prepared from either crude or highly purified streptokinase and highly purified human plasminogen. The activator complex gave a single component in starch gel electrophoresis, in either lysine or E-aminocaproic acid buffers, and in immunochemical studies with a specific rabbit antibody to human plasminogen. However, the mobility of the activator was different from human plasmin, human plasminogen, or streptokinase both in starch gel electrophoresis and in immunoelectrophoresis. The activator can be dissociated into two components, apparently corresponding to streptokinase and human plasmin, by electrophoresis in starch gels. Gel diffusion analyses with specific antibody revealed that the activator was immunologically identical with both human plasmin and human plasminogen. In sedimentation velocity experiments, the activator showed a single component in e-aminocaproic acid buffers with a sedimentation coefficient of approximately 5 S. In lysine buffers, activator showed some heterogeneity, but the sedimentation coefficient of the major component was found to be approximately 11 S. The apparent molecular weight of activator by sedimentation equilibrium methods, in ~aminocaproic acid buffers, was found to be approximately 150,000. In lysine buffers the apparent molecular weight in dilute solutions was found to be approximately 138,000, whereas in concentrated solutions the molecular weight was found to be approximately 308,000. These data suggest a possible monomer-dimer relationship which is concentration dependent. The dimer form appeared to be present when activator was dissolved in lysine buffers, in concentrated solutions only, whereas the monomer form was always found when activator was dissolved in c-aminocaproic acid buffers.