Plasminogen activation in diabetes mellitus. Kinetic analysis of plasmin formation using components isolated from the plasma of diabetic donors.

Two components of the fibrinolytic system, plasminogen and the vascular plasminogen activator, have been isolated to apparent homogeneity from the post-venous occlusion plasma of three diabetic patients (hemoglobin A1C greater than 7%) and of one nondiabetic control person. Plasminogen activation was studied for each person separately in the absence and presence of CNBr fragments of fibrinogen. Activation of diabetic plasminogen by urokinase was not significantly altered as compared to the activation of control plasminogen. The same was found when diabetic plasminogen was activated by control vascular plasminogen activator in the presence of fibrinogen fragments but only at plasminogen concentrations below 10-30 nM; at higher substrate concentrations, however, plasminogen activation was impaired in a pattern resembling substrate inhibition. Activation of control plasminogen by diabetic vascular plasminogen activator was completely impaired in the absence of fibrinogen fragments. Addition of fibrinogen fragments stimulated plasmin formation by diabetic vascular plasminogen activator resulting in kinetic constants which were similar to the activation of control plasminogen by control vascular plasminogen activator in the absence of fibrinogen fragments (Km = 7.5 microM, kcat = 0.05 S-1). Addition of fibrinogen fragments in controls decreased Km values to less than 0.1 microM. Despite addition of fibrinogen fragments the rate of plasmin formation from diabetic plasminogen by diabetic vascular plasminogen activator isolated from the same diabetic donor was so small that kinetic constants could not be calculated.