Activity of the alpha 2-macroglobulin-plasmin complex on the plasmin specific substrate H-D-Val-Leu-Lys-p-nitroanilide

An α 2 -macroglobulin-plasmin complex was prepared by incubation of plasmin with an excess of purified α 2 -macroglobulin. The conditions for complex formation were analysed, and formation of a complex was confirmed by crossed immunoelectrophoresis and by activity measurements on fibrin and p-tosyl-L-arginine methyl ester. The experiments indicated binding of no more than one mole of plasmin per mole of α 2 -macroglobulin. The activity of the α 2 -macroglobulin-plasmin complex and free plasmin on the plasmin specific substrate H-D-Val-Leu-Lys-p-nitroanilid was investigated under various conditions. The activity of the complex was found to be about 50% of that of free plasmin. An increase in ionic strength increased the activity of free plasmin, while the activity of the complex was essentially unaffected. There were no differences in pH-optima or Michaelis constant for free and α 2 -macroglobulin-bound plasmin.