Insulin receptors are bivalent as demonstrated by photoaffinity labeling.
Insulin receptors in human placental membranes were photoaffinity-labeled with a radioactive human insulin-like growth factor I (hIGF-I) photoprobe N epsilon B28-monoazidobenzoyl 125I-hIGF-I either alone or together with a non-radioactive insulin photoprobe N epsilon B29-monoazidobenzoyl insulin. Precipitation of the solubilized receptors with anti-insulin antibody showed that receptors labeled with the radioactive hIGF-I photoprobe were detected in the immunoprecipitate only when photolabeling was carried out in the presence of the non-radioactive insulin photoprobe. Comparable results were obtained in converse experiments using a radioactive insulin photoprobe N epsilon B29-monoazidobenzoyl 125I-insulin, a non-radioactive hIGF-I photoprobe N epsilon B28-monoazidobenzoyl hIGF-I, and an antibody to hIGF-I. The amount of radioactive receptors precipitated by either the anti-insulin antibody or the anti-hIGHF-I antibody was close to the expected amount. These observations demonstrate that the insulin receptor is bivalent being capable of binding two molecules of ligand.
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Banting and Best Department of Medical Research, University of Toronto, Toronto, Ontario, Canada.
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D000345:Affinity Labels; D001345:Autoradiography; D001667:Binding, Competitive; D005260:Female; D006801:Humans; D007328:Insulin / Q000276:immunology; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D010777:Photochemistry; D010920:Placenta / Q000378:metabolism; D011233:Precipitin Tests; D011247:Pregnancy; D011972:Receptor, Insulin / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism
D000345:Affinity Labels; D007328:Insulin; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D011972:Receptor, Insulin