Sialic Acid Content of Plasminogen 2 Glycoforms as a Regulator of Fibrinolytic Activity

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 × 106M−1 s−1 to 3.77 × 104M−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 α2-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 α2-antiplasmin; however, hypersialylated plasmin does not appear to have a kringle-dependent component to inhibition.