An Alteration in Apparent Molecular Weight of the Insulin Receptor from the Human Monocyte Cell Line U-937

We have studied the structure of the insulin receptor from a human cultured monocyte cell line, U-937. The receptor is composed of alpha and beta subunits as seen in other insulin receptors, but these subunits are of greater apparent molecular weight (alpha 150,000 and beta 102,000) than in typical insulin receptors. Despite this, the U-937 insulin receptor appears to function normally. The alpha subunit binds insulin and the beta subunit is phosphorylated in response to insulin stimulation. Both subunits are expressed in the plasma membrane. Insulin binding isotherms are similar to those seen in IM-9 lymphocytes. Thus, the insulin receptor from U-937 monocytes appears functionally normal despite alterations in molecular weight of the subunits.