Proteolytic fragments of the receptors for IgE

Partially purified IgE receptor(s) of rat basophilic leukemia cells (RBL) designated R and H and having apparent molecular weight of 45,000 and 55,000 daltons, respectively, were subjected to proteolysis with papain. Polyacrylamide gel electrophoresis of the digests in the presence of sodium dodecyl sulfate revealed a difference in the size and number of the fragments produced. These results suggest that these two receptor molecules are different with respect to amino acid composition and sequence. Whole Nonidet P-40 extracts of RBL cells were also subjected to digestions with papain, trypsin and chymotrypsin in an attempt to obtain receptor fragments still capable of binding to IgE-Sepharose. Treatment with papain produced a 38,000 dalton fragment of H but no fragments of R which retained the ability to bind to IgE. Tryptic and chymotryptic treatment produced a 41,000 dalton fragment of H with affinity for IgE. The IgE-binding site of R was either destroyed or not affected at all.