[47] Radioactive labeling and turnover studies of the insulin receptor subunits

The insulin receptor is an integral membrane protein composed of two major subunits of approximate molecular weights 135,000 and 95,000. Like other cellular proteins, the concentration of the receptor is the result of a dynamic equilibrium between the processes of synthesis and degradation. The study of biosynthetic and degradative processes of the life cycle of the insulin receptor requires the use of adequate probes for measuring the receptor independent of its ability to bind insulin. Immunological probes human autoantibodies are used from diabetic patients with a rare form of insulin resistance and acanthosis nigricans. The specificity of these autoantibodies to the insulin receptor is based on a number of studies. These antibodies can immunoprecipitate quantitatively the solubilized insulin receptor. The receptors are identified among all the labeled cellular proteins by immunoprecipitation of the detergent-solubilized cellular extracts with anti-receptor antibodies. The immunoprecipitated receptors are analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography.