[Ability of bovine fibrinogen to accept and retain plasminogen proactivator specific for human blood]

The plasminogen proactivator present in human plasma and retained by purified human fibrinogen preparations is readily accepted and retained by bovine fibrinogen. This "transplantation" makes isolated bovine fibrinogen susceptible to streptokinase. The latter induces degradation of isolated bovine fibrinogen resulting in characteristic fragment formation. Our experimental results, particularly those showing the inability of bovine plasminogen (applied in a great excess) to remove the acquired proactivator from bovine fibrinogen, give indirect evidence that the proactivator function is not a specific property of the human plasminogen but that of some other substance.