Partial purification and properties of a plasminogen activator from human erythrocytes

The lysis time of euglobulin clots made with whole blood (plasma and red cells) was very much shorter than that of clots made with plasma alone, indicating a fibrinolytic component in red cells. A plasminogen activator was found in the stroma-free hemolysate, and proteolytic activity was found in the stromal fraction. The plasminogen activator, purified by using diethylaminoethyl-cellulose (DEAE-cellulose) in a batch procedure followed by column chromatography, was called erythrokinase (EK). On preliminary characterization, EK appears to activate human and bovine plasminogen in a manner similar to urokinase (UK), as determined by fibrinolytic and caseinolytic assays. The two enzymes can be separated by DEAE chromatography and acrylamide-gel electrophoresis, however, and they hydrolyze acetyl-L-lysine methyl ester and benzoyl arginine methyl ester at different rates.