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 plasminogen activation by bovine urokinase-type and tissue-type plasminogen activators. All individual caseins (alpha-CN, beta-CN, and kappa-CN) enhanced the activity of both types of plasminogen activators. Optimal concentrations for alpha-CN and beta-CN were 5 and 25 micrograms/ml, respectively. The enhancement of enzymatic activity declined when concentrations of alpha-CN and beta-CN were higher. In contrast, increasing concentrations of kappa-CN from 0 to 200 micrograms/ml resulted in corresponding increases in activity of both types of plasminogen activators. On a weight basis, alpha-CN was the most effective enhancer of plasminogen activator activity. Indirect evidence obtained with experiments utilizing alpha-CN immobilized on agarose suggested that the effect is related to extensive binding of plasminogen and both types of plasminogen activators to casein.