H-D-val-leu-lys-aminoisophthalic acid, dimethyl ester, is sensitive to streptokinase-activator not to plasmin.

The ability of human plasma and purified human plasmin and plasminogen to hydrolyze a new synthetic substrate, H-D-valine-leucine-lysine-5-aminoisophthalic acid, dimethyl ester, ditrifluoroacetate, was studied. Contrary to published data, we found this substrate was only minimally hydrolyzed by plasmin or urokinase-treated plasminogen or plasma. Plasminogen-free bovine fibrinogen was readily degraded by plasmin and urokinase-activated plasminogen. However, in the presence of streptokinase, the synthetic substrate was highly sensitive to human plasma and purified plasmin and plasminogen. Apparently, the substrate is specific for streptokinase-plasmin and streptokinase-plasminogen activators, not for plasmin.