The incorporation of tritiated precursors into receptors for IgE of rat basophilic leukemia cells.

It has previously been shown that two receptors, H and R, having apparent mol. wt of 55,000 and 45,000 daltons, can be isolated from surface iodinated RBL cells. In addition, small amounts of a third molecule of 71,000 daltons (71 K) can now be detected in receptor preparations isolated by means of IgE-Sepharose. The SDS-PAGE patterns show that the three surface molecules were not significantly altered when cell solubilization was carried out in the presence of protease inhibitors. The same three molecules were also observed when cells were biosynthetically labelled with [3H]-fucose of [3H]-galactose. When cells were labelled with [3H]-leucine or [3H]-tyrosine, several additional molecules were observed in IgE-Sepharose purified preparations. When cells were exposed to free IgE- before solubilization, significant inhibition of binding to IgE-Sepharose could only be seen among molecules corresponding to H, R and 71 K. When receptors were isolated by means of DNP-IgE and anti-DNP-Sepharose, fewer molecules were found. One, which was frequently observed, had a mol. wt of 26,000 daltons. This molecule may be non-covalently associated with receptors for IgE.