Reaction of 5-iodonaphthyl-1-nitrene with the IgE receptor on normal and tumour mast cells

Abstract

Mast cells, basophils and a tumor analog, rat basophilic leukemia (RBL) cells, have a surface glycoprotein (R.epsilon.) which specifically binds monomeric immunoglobulin E (IgE), and aggregation of R.epsilon. causes secretion. When isolated from non-ionic detergent extracts of surface-labeled RBL cells by IgE-specific immunoprecipitation, R.epsilon. appears as a 50,000 (50 K [kilodalton]) to 60,000 (60 K) MW band on electrophoresis in polyacrylamide gels in SDS (SDS-PAGE [sodium dodecyl sulfate-polyacrylamide gel electrophoresis]). Likewise, only a 50 K component is observed when the polypeptide that binds IgE is isolated by affinity chromatography in conditions which prevent aggregation of the IgE, even when intrinsically labeled R.epsilon. is studied. To determine how R.epsilon. is inserted into the plasma membrane, RBL cells were reacted with the photolysable hydrophobic reagent 5-iodonaphthyl-1-azide (INA), which preferentially labels the intramembranous segments of several intrinsic membrane proteins. The label was found, not on the 50 K glycopeptide, but only on a 30 K component which other studies suggest is a subunit of R.