Summary
Milk plasminogen-activator was partially purified from human transitional milk collected
at about 10 days after delivery, by a five-step procedure involving chloroform treatment,
ammonium sulfate precipitation, and column chromatography on Sephadex G-150, CM Sephadex
C-50 and DEAE Sephadex A-50. This gave milk-activator with a maximum purification
factor of about 2,400-fold with respect to the skimmed milk. The CM Sephadex-step
preparation showed, on polyacrylamide gel electrophoresis, a single plasminogen-activator
activity band located between the bands of albumin and prealbumin of human serum.
This preparation exhibited no kinin forming activity. The activator hydrolyzed acetyl-glycyl-L-lysine
methyl ester with similar order kinetic constants to urokinase, and was inhibited
strongly by diisopropyl-fluorophosphate. The molecular weight of the activator as
estimated by gel filtration was approximately 86,000, the isoelectric points as estimated
by gel isoelectric focusing were pH 7.2, 6.9 and 6.6, and the activator activity was
not quenched by antiurokinase globulin, indicating that the milk-activator is a different
entity from urokinase.
Keywords
Plasminogen-activator - Milk-activator - Fibrinolysis
