Characterization, size estimation and solubilization of alpha-macroglobulin complex receptors in liver membranes.
Receptors for alpha 2-macroglobulin-proteinase complexes have been characterized in rat and human liver membranes. The affinity for binding of 125I-labelled alpha 2-macroglobulin.trypsin to rat liver membranes was markedly pH-dependent in the physiological range with maximum binding at pH 7.8-9.0. The half-time for association was about 5 min at 37 degrees C in contrast to about 5 h at 4 degrees C. The half-saturation constant was about 100 pM at 4 degrees C and 1 nM at 37 degrees C (pH 7.8). The binding capacity was approx. 300 pmol per g protein for rat liver membranes and about 100 pmol per g for human membranes. Radiation inactivation studies showed a target size of 466 +/- 71 kDa (S.D., n = 7) for alpha 2-macroglobulin.trypsin binding activity. Affinity cross-linking to rat and human membranes of 125I-labelled rat alpha 1-inhibitor-3.chymotrypsin, a 210 kDa analogue which binds to the alpha 2-macroglobulin receptors in hepatocytes (Gliemann, J. and Sottrup-Jensen, L. (1987) FEBS Lett. 221, 55-60), followed by SDS-polyacrylamide gel electrophoresis, revealed radioactivity in a band not distinguishable from that of cross-linked alpha 2-macroglobulin (720 kDa). This radioactivity was absent when membranes with bound 125I-alpha 1-inhibitor-3 complex were treated with EDTA before cross-linking and when incubation and cross-linking were carried out in the presence of a saturating concentration of unlabelled complex. The saturable binding activity was maintained when membranes were solubilized in the detergent 3-[(3-cholamidopropyl)dimethylammonio]propane sulfonate (CHAPS) and the size of the receptor as estimated by cross-linking experiments was shown to be similar to that determined in the membranes. It is concluded that liver membranes contain high concentrations of an approx. 400-500 kDa alpha 2-macroglobulin receptor soluble in CHAPS. The soluble preparation should provide a suitable material for purification and further characterization of the receptor.
Gliemann
J
J
Institute of Physiology, University of Aarhus, Denmark.
Davidsen
O
O
Moestrup
S K
SK
D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism; D003432:Cross-Linking Reagents; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D046911:Macromolecular Substances; D051381:Rats; D011971:Receptors, Immunologic / Q000032:analysis*; D012995:Solubility; D000511:alpha-Macroglobulins / Q000378:metabolism*
D003432:Cross-Linking Reagents; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D046911:Macromolecular Substances; D011971:Receptors, Immunologic; D000511:alpha-Macroglobulins