A Radioimmunoassay for Human Insulin Receptor Correlation Between Insulin Binding and Receptor Mass

Summary

We have developed a radioimmunoassay for human insulin receptor. Serum from a patient with Type B severe insulin resistance was used as anti-insulin receptor antiserum. Pure human placental insulin receptor was used as reference preparation and ¹²⁵I labeled pure insulin receptor as trace. The radioimmunoassay was sensitive (limit of detection < 17 fmol), reproducible (inter and intra-assay coefficients of variation 12.5% and 1.6% respectively) and specific (no crossreactivity with pure placental IGF-1 receptor, insulin and glucagon). The anti-insulin receptor antibody was, however, able to differentiate between insulin receptor from human placenta and from rat liver.

To determine the number of insulin binding sites per receptor, we measured insulin binding (by insulin binding assay) and insulin receptor mass (by radioimmunoassay) in solubilized aliquots from 5 human placentas. The molar ratio of insulin binding to receptor mass was 0.86 ± 0.12 when binding was determined with monoiodinated ¹²⁵I-Tyr A¹⁴-insulin. It was 1.94 ± 0.27 when randomly iodinated ¹²⁵I-insulin was used.

In conclusion, using a sensitive, reproducible and specific radioimmunoassay, we have measured insulin receptor mass independent of insulin binding. Our data are most compatible with binding of one insulin molecule per human placental insulin receptor.

Key words

Human Insulin Receptor RIA - Receptor Mass - Insulin Binding - Monoiodinated Tyr A¹⁴-Insulin - IGF-1