Binding and endocytosis of alpha 2-macroglobulin-plasmin complexes.
The clearance of 125I-labeled alpha 2-macroglobulin-plasmin complexes (125I-alpha 2M-PM) from mouse circulation is slower than that of 125I-labeled alpha 2M-methylamine complexes (125I-alpha 2M-CH3NH2). In addition, clearance of 125I-alpha 2M-PM is biphasic, but that of 125I-alpha 2M-CH3NH2 follows simple first-order kinetics. Treatment of alpha 2M-PM with trypsin yields a complex that clears like alpha 2M-CH3NH2. Complexes of alpha 2M with Val442-plasmin (alpha 2M-Val442-PM) were prepared; alpha 2M-Val442-PM has a stoichiometry of 2 mol of Val442-PM to 1 mol of alpha 2M and also clears like alpha 2M-CH3NH2. In vitro 4 degrees C binding inhibition studies with mouse peritoneal macrophages show that alpha 2M-CH3NH2, alpha 2M-PM, trypsin-treated alpha 2M-PM, and alpha 2M-Val442-PM bind with the same affinity, apparent Kd = 0.4 nM. The binding isotherms at 4 degrees C are the same for 125I-alpha 2M-CH3NH2, 125I-alpha 2M-PM, and 125I-trypsin-treated alpha 2M-PM in both mouse peritoneal macrophages and 3T3-L1 fibroblasts. The Scatchard plots for the binding isotherms in macrophages were curved; those in 3T3-L1 fibroblasts were linear with an apparent Kd of 0.48 nM and a receptor activity of 140 fmol/mg of cell protein for alpha 2M-CH3NH2, an apparent Kd of 0.29 nM and a receptor activity of 110 fmol/mg of cell protein for alpha 2M-PM, and an apparent Kd of 0.35 nM and a receptor activity of 210 fmol/mg of cell protein for trypsin-treated alpha 2M-PM.(ABSTRACT TRUNCATED AT 250 WORDS)
K A
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Ney
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Gidwitz
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Pizzo
D000818:Animals; D002478:Cells, Cultured; D004705:Endocytosis; D005341:Fibrinolysin / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D051379:Mice; D010958:Plasminogen / Q000378:metabolism; D011485:Protein Binding; D014357:Trypsin; D000511:alpha-Macroglobulins / Q000378:metabolism*
D046911:Macromolecular Substances; D000511:alpha-Macroglobulins; C024668:plasmin-alpha(2)-macroglobulin complex; D010958:Plasminogen; D014357:Trypsin; D005341:Fibrinolysin