Binding and endocytosis of alpha 2-macroglobulin-plasmin complexes

Biochemistry. 1985 Aug 13;24(17):4586-92. doi: 10.1021/bi00338a016.


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)

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Cells, Cultured
  • Endocytosis
  • Fibrinolysin / metabolism*
  • Fibroblasts / metabolism
  • Humans
  • Kinetics
  • Macromolecular Substances
  • Mice
  • Plasminogen / metabolism
  • Protein Binding
  • Trypsin
  • alpha-Macroglobulins / metabolism*


  • Macromolecular Substances
  • alpha-Macroglobulins
  • plasmin-alpha(2)-macroglobulin complex
  • Plasminogen
  • Trypsin
  • Fibrinolysin