Sialic acid content of plasminogen 2 glycoforms as a regulator of fibrinolytic activity. Isolation, carbohydrate analysis, and kinetic characterization of six glycoforms of plasminogen

Six glycoforms of plasminogen 2 were isolated using a combination of lectin affinity chromatography and chromatofocussing, and the sialic acid content of each glycoform was determined. The kinetics of activation of each glycoform by tissue-type plasminogen activator were analyzed on a fibrin surface and in solution. The second-order rate constant (measured on a fibrin surface) decreased from 1.65 x 10(6) M-1 s-1 to 3.77 x 10(4) M-1 s-1 as the sialic acid content of the glycoforms increased from 1.3 mol/mol of protein to 13.65 mol/mol of protein. A similar correlation was noted for activation in solution. Each glycoform was converted to plasmin, and the inhibition constants for the reaction between alpha 2-antiplasmin and plasmin glycoforms were determined. All overall Ki values, reflecting the final essentially irreversible complex, were in the picomolar range. Sialic acid does not affect inhibition of plasmin by alpha 2-antiplasmin; however, hypersialylated plasmin does not appear to have a kringle-dependent component to inhibition.