Lipoprotein (a) and plasminogen are immunochemically related.

Earlier studies demonstrated that lipoprotein (a), a lipoprotein of high atherogenicity, possesses proteolytic activity. In this report, we provide evidence that the lipoprotein (a)-specific antigen, apoprotein (a) is immunochemically related to plasminogen. This was demonstrated by polyclonal antisera from rabbit, sheep and horse, and with three monoclonal antibodies from mouse. Using immunospecific adsorbers against lipoprotein (a), all plasminogen could be adsorbed from lipoprotein (a)-positive and apparently lipoprotein (a)-negative plasma. As an additional similarity to plasminogen, lipoprotein (a) binds selectively to lysine-Sepharose, but with a somewhat lower affinity. In an assay system for measuring the fibrinolytic activity challenged with streptokinase, lipoprotein (a) prolonged strikingly the fibrinolysis time under certain experimental conditions.