Unexpected findings from target analysis of immunoglobulin E and its receptor

The membrane receptor for immunoglobulin E (IgE) and its ligand, IgE, were irradiated with high-energy electrons. Loss of binding activity was measured for each, and the size of the functional targets was assessed. In both cases, the target size was substantially smaller than the covalent structure of the molecule. The direction of this discrepancy is unprecedented on the basis of experience with loss of enzymatic activity by irradiation; indeed, two enzymes which were present in the receptor preparations gave expected values when measured simultaneously. We suggest that in instances where a function such as ligand binding resides in a conformationally stable domain, radiation inactivation may be capable of revealing this.