Further characterization of the beta-component of the receptor for immunoglobulin E

A 30,000 mol. wt component (beta) is associated in a 1:1 ratio with the 50,000 mol. wt glycoprotein (alpha) which binds immunoglobulin E (IgE) on mast cells and related tumor cells. We show that alpha and beta are associated in membrane preparations. This is consistent with previous results which showed labeling of beta with the hydrophobic probe 5-iodonaphthyl-1-azide (INA). The beta-polypeptide is susceptible to proteolytic cleavage during preparation of the membranes and when this occurs a 20,000 fragment can be labeled with INA and remains associated with alpha. No incorporation of carbohydrate precursors into beta was observed. Since beta is also not modified when cells are surface-labeled, it may not be exposed on the cell surface. Rigorous washing of IgE-receptor complexes with non-ionic detergent results in dissociation of beta from the alpha-IgE complex. The latter will then not reassociate with beta when exposed to crude detergent extracts of the tumor cells.