EFFECT OF INDIVIDUAL CASEINS ON PLASMINOGEN ACTIVATION BY BOVINE UROKINASE-TYPE AND TISSUE-TYPE PLASMINOGEN ACTIVATORS

The effect was examined of individual caseins on the rate of plasminog en activation by bovine urokinase-type and tissue-type plasminogen act ivators. All individual caseins (alpha-CN, beta-CN, and kappa-CN) enha nced the activity of both types of plasminogen activators. Optimal con centrations for alpha-CN and beta-CN were 5 and 25 mu g/ml, respective ly. The enhancement of enzymatic activity declined when concentrations of alpha-CN and beta-CN were higher. In contrast, increasing concentr ations of kappa-CN from 0 to 200 mu g/ml resulted in corresponding inc reases in activity of both types of plasminogen activators. On a weigh t basis, alpha-CN was the most effective enhancer of plasminogen activ ator activity. Indirect evidence obtained with experiments utilizing a lpha-CN immobilized on agarose suggested that the effect is related to extensive binding of plasminogen and both types of plasminogen activa tors to casein.