title: Binding of asialotransferrins by purified rat liver plasma membranes.
abstract: Interaction of four different asialotransferrins (human types 1, 2, and 3, and rabbit asialotransferrin) with purified plasma membranes from the rat liver was studied by using a direct binding assay. Binding of rabbit asialotransferrin, possessing a single biantenary glycan, was too weak to establish a complete binding curve, but the human asialotransferrins, possessing two glycan attachments, did yield binding data over a sufficiently wide range of concentrations for Scatchard plot analysis. At 22 degrees C, a quantity of plasma membrane equivalent to 1 mg of membrane protein bound comparable quantities (12.3-12.8 pmol) of the asialotransferrin types with an association constant of 1.5 X 10(6) M-1 for type 1, 1.4 X 10(7) M-1 for type 2, and 1.1 X 10(8) M-1 for type 3. At 4 degrees C, the number of binding sites and the association constants were reduced, more so for asialotransferrin types 2 and 3 than for type 1. At both temperatures, the shapes of the Scatchard plots for all three asialotransferrin types were similar: in the low range of bound asialoprotein (below 0.6-0.7 nM), each plot exhibited two to three convex peaks, tentatively identified as restricted domains of positive cooperativity; in the higher range, however, the plots were linear. The findings are consistent with the view that the binding sites involved in the binding of asialotransferrin are homogenous.
mesh_terms: D000818:Animals; D001212:Asialoglycoproteins; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D011485:Protein Binding; D011817:Rabbits; D051381:Rats; D014168:Transferrin / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D001212:Asialoglycoproteins; D014168:Transferrin; C017031:asialotransferrins