Kringle 5 of human plasminogen carries a benzamidine-binding site

Affinity of plasminogen fragments for p-aminobenzamidine-Sepharose was investigated to localize the benzamidine-binding site(s) of the protein. i/ Of the elastase fragments of plasminogen only miniplasminogen (kringle 5 plus light chain) was bound to the column. Kringle 1+2+3 and kringle 4, which carry the lysine-binding sites, were not adsorbed, proving that the lysine-and benzamidine-binding sites are on different domains of the protein. ii/ Light chain was bound to the column even if the primary benzamidine-binding site was covalently blocked, indicating that the protease part of plasmin has a second benzamidine-binding site. iii/ Kringle 5 also binds to the affinity column: the presence of a binding site on kringle 5 raises the possibility that this structure may take part in the interactions of plasminogen with other proteins.