Molecular weight and valence of the cell-surface receptor for immunoglobulin E

The molecular weight of the active solubilized cell-surface receptor for immunoglobulin E (IgE) was measured in nonionic detergent. The diffusion coefficient was estimated by gel filtration, the partial specific volume was estimated from the differential sedimentation in sucrose gradients prepared from H2O and D2O, and the sedimentation constant was estimated from the same centrifugation experiments. The receptor has an apparent molecular weight of 130,000. Its high partial specific volume (0.81 cm3/g) suggests that bound detergent contributes significantly to the mass. The molecular weights of the receptor-IgE complex and of unbound IgE determined similarly were 310,000 and 200,000 respectively, clearly showing that the receptor is univalent. The implications of these results for the subunit structure of the receptor, receptor-membrane integration, and a possible mechanism of receptor triggering are discussed.