The rat basophilic leukemia cell receptor for IgE. I. Characterization as a glycoprotein

Rat basophilic leukemia cells were labeled either enzymically with ¹²⁵I or biosynthetically by culture in the presence of ¹⁴C glucosamine or ³H amino acids and then extracted with NP 40. IgE anti IgE precipitates insolubilized a radiolabeled macromolecule from these extracts largely or entirely absent in control IgG anti IgG precipitates. When specific precipitates were boiled in sodium dodecyl sulfate (SDS) and analyzed by polyacrylamide gel electrophoresis in the presence of SDS, most of the ¹⁴C or ¹²⁵I radioactivity was in the area corresponding to an apparent m.w. of 60,000 to 70,000 in 5.9% gels. In 10% and 12% gels, faster mobility was demonstrated indicating an atypical electrophoretic behavior often associated with glycoproteins and a presumptive m.w. of 50,000 or less. Since only IgE containing precipitates localized label in this region and since such precipitates from cells saturated with IgE prior to surface iodination failed to show this band, the labeled macromolecule appears to be the IgE receptor itself. Analysis of the acid hydrolysates of precipitated ¹⁴C radioactivity demonstrated that label was entirely in hexosamines and sialic acid. ¹²⁵I and ¹⁴C labels in the receptor region were eliminated almost completely with pepsin and pronase and to a lesser extent with trypsin.