Human plasminogen: a summary of studies on its isolation, characterization and activation mechanism.

For the isolation of plasminogen the method of affinity chromatography is superior to conventional fractionation procedures. These may lead to partially degraded plasminogen, if no care is taken to inhibit traces of contaminating plasmin. Presumably intact plasminogen, as isolated from plasma by affinity chromatography with polyacrylamide-lysine as the specific adsorbent, is characterized by a mol. wt of 92–93,000 and NH₂-terminal glutamic acid.During activation with urokinase a peptide moiety of at least 5000 mol. wt is liberated from the NH₂-terminal region of the proenzyme. The remaining inactive intermediate (mol. wt 84,000 NH₂-terminal valine) is cleaved in a second step to yield the plasmin molecule which is composed of two chains with mol. wt of 24,000 (light chain) and 60,000 (heavy chain).After mild reduction of the only interchain disulfide bridge in plasmin the heavy chain was isolated by adsorption on polyacrylamide-lysine. This chain showed pronounced changes in the values of the sedimentation and diffusion constants as a function of the ϵ-aminocaproic acid concentration. The behavior towards ϵ-aminocaproic acid suggests that inhibitor binding site is located in the heavy chain and that the inhibition of plasmin by ϵ-aminocaproic acid is caused primarily by inhibitor induced conformational alterations of the heavy chain.