The receptor for immunoglobulin E: examination for kinase activity and as a substrate for kinases

Purified receptor-immunoglobulin E (IgE) complexes incubated with [gamma-32P]-ATP incorporated phosphorus into tyrosines on the beta and gamma chains of the receptor. The activity had the typical characteristics of a tyrosine kinase. Immunoprecipitation of the complexes with anti-IgE left the activity in the supernatant, demonstrating that the receptor itself was not the kinase. The receptor was also phosphorylated when membranes or intact cells were incubated with radioactive ATP or phosphate, respectively, but in each case the subunits or amino acid residues that were modified were distinctive.