Association of alpha 2-macroglobulin-thrombin and alpha 2-macroglobulin-plasmin complexes with isolated hepatocytes.
125I-labelled alpha 2-macroglobulin complexed with thrombin or plasmin bound to hepatocytes in a concentration- and time-dependent manner. The apparent Kd values calculated from displacement experiments were 7.9 X 10(-8) M for alpha 2-macroglobulin-thrombin and 8.5 X 10(-8) M for alpha 2-macroglobulin-plasmin. Association of these complexes was only partially reversible; after a 180 min incubation period, 50-60% of the bound radioactivity was internalized by the cells. alpha 2-Macroglobulin itself bound also to hepatocytes, but the affinity of the alpha 2-macroglobulin complexes was higher than that of the inhibitor alone, and alpha 2-macroglobulin was not internalized, either. 125I-labelled thrombin or plasmin bound to hepatocytes as well. These bindings were also concentration-dependent and could be decreased with an excess of unlabelled ligands. Binding rates and amounts of the bound proteinases were higher than those of their alpha 2-macroglobulin complexes. The alpha 2-macroglobulin-thrombin complex competed with the alpha 2-macroglobulin-plasmin complex in binding to hepatocytes, whereas there was no competition between these complexes and the antithrombin III-thrombin complex. These results suggest that the binding sites of hepatocytes for alpha 2-macroglobulin-proteinase and antithrombin III-proteinase complexes are different.
Spolarics
Z
Z
Mandl
J
J
Machovich
R
R
Lambin
P
P
Garzó
T
T
Antoni
F
F
Horváth
I
I
D000818:Animals; D000990:Antithrombin III / Q000378:metabolism; D001665:Binding Sites; D001667:Binding, Competitive; D005341:Fibrinolysin / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D051379:Mice; D013917:Thrombin / Q000378:metabolism*; D000511:alpha-Macroglobulins / Q000378:metabolism*
D000511:alpha-Macroglobulins; C024668:plasmin-alpha(2)-macroglobulin complex; D000990:Antithrombin III; D013917:Thrombin; C046034:thrombin alpha 2-macroglobulin complex; D005341:Fibrinolysin