| Abstract: | Cell surface receptors for immunoglobulin E were isolated by repetitive affinity chromatography from rat basophilic leukemia cells biosynthetically labeled with L-35S]methionine and D-3H]mannose. Native immunoglobulin E receptor appeared as a very broad band in the 45,000 to 62,000 Mr region in sodium dodecyl sulfate polyacrylamide gels. However, from cells cultured in the presence of tunicamycin, a relatively narrow band with an apparent Mr of 38,000 was isolated. The 38,000 Mr band rebound to immunoglobulin E-Sepharose, was immunoprecipitated with antibodies to immunoglobulin E receptor, shared tryptic peptides with native receptor, and was labeled with L-35S]methionine but not D-3H]mannose, and thus appears to be immunoglobulin E receptor lacking N-linked oligosaccharides. It is demonstrated that N-linked oligosaccharides account for much of the apparent heterogeneity of native receptor in sodium dodecyl sulfate polyacrylamide gels and in two-dimensional gel electrophoresis. A receptor-associated protein with apparent Mr = 30,000, prominently labeled with L-35S]methionine but not with D-3H]mannose, did not have altered molecular properties when isolated from tunicamycin-cultured cells, and did not share tryptic peptides with receptor. |
