title: Partial purification and characterization of a new fast-acting plasmin inhibitor from human platelets. Evidence for non-identity with the known plasma proteinase inhibitors.
abstract: An inhibitor of the plasma proteinase plasmin (EC 3.4.21.7) was partially purified from washed and lysed human blood platelets by (NH4)2SO4 fractionation and affinity chromatrography on Sepharose-linked purified plasminogen. The material contained none of the known plasma proteinase inhibitors when studied by crossed-immunoelectrophoresis and electroimmunoassay, but inhibited a clot-lysis-time assay and an esterolytic assay that used the synthetic substrate S-2251 (D-Val-Leu-Lys-p-nitroanilide). The inhibitory activity had the same mobility as the alpha 2-plasma proteins on preparative agarose-gel electrophoresis. Titration of the inhibitor preparation by active-site-titrated plasmin demonstrated a dissociation constant of approx. 0.1 nM. The inhibition was complete within 1 min. The inhibitor increased the mobility in agarose-gel electrophoresis of purified activator-free plasmin or 125I-labelled plasmin, as demonstrated by crossed-immunoelectrophoresis against specific immunoglobulins against plasminogen or by radioautography. The results strongly suggest the presence in platelets of a plasmin inhibitor different from the known plasma proteinase inhibitors.
mesh_terms: D001792:Blood Platelets / Q000201:enzymology*; D002846:Chromatography, Affinity; D005341:Fibrinolysin / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D007123:Immunoelectrophoresis, Two-Dimensional; D008970:Molecular Weight; D011480:Protease Inhibitors / Q000097:blood* / Q000302:isolation & purification
chemical_list: D011480:Protease Inhibitors; D005341:Fibrinolysin