title: Changes in the binding of "fast"-form alpha 2-macroglobulin to 3T3-L1 cells after differentiation to adipocytes.
abstract: Human alpha 2-macroglobulin (alpha 2M)-CH3NH2 specifically binds to 3T3-L1 fibroblasts and adipocytes with an apparent Kd of 0.3 nM at 4 degrees C. Binding to fibroblasts follows first-order kinetics only for the first 20-30 min of reaction, k1 = 160 microM-1 h-1, and then proceeds in a non-first-order reaction that takes 28 h to reach steady state. Receptor activity is 120 fmol of alpha 2M-CH3NH2/mg of cell protein or 60 000 molecules/cell. Binding is nondissociable. In contrast, binding to adipocytes follows first-order kinetics, k1 = 720 microM-1 h-1, and reaches steady state in 6-8 h. Receptor activity is 35 fmol of alpha 2M-CH3NH2/mg of cell protein or 60 000 molecules/cell. Binding is reversible with a k2 of 0.4 h-1. Control studies with 3T3-C2 cells, which do not differentiate after hormone treatment, indicate that these differences are not due to hormone treatment alone. Binding to both fibroblasts and adipocytes is specific for "fast"-form alpha 2M but not for native alpha 2M. Inhibition studies with neoglycoproteins demonstrate that binding does not occur via any of the known carbohydrate receptors. Some cross-reactivity with antithrombin III-trypsin complexes is demonstrated. Both fibroblasts and adipocytes take up and degrade alpha 2M-CH3NH2 at 37 degrees C. For both cell types, the concentration of alpha 2M-CH3NH2 needed for half-maximal uptake is 65 nM.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000273:Adipose Tissue / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D002454:Cell Differentiation; D002478:Cells, Cultured; D006801:Humans; D007700:Kinetics; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D051379:Mice; D011971:Receptors, Immunologic / Q000378:metabolism*; D000511:alpha-Macroglobulins / Q000378:metabolism*
chemical_list: D026503:Low Density Lipoprotein Receptor-Related Protein-1; D011971:Receptors, Immunologic; D000511:alpha-Macroglobulins