Dephosphorylation of the hepatic insulin receptor: absence of intrinsic phosphatase activity in purified receptors.

We have compared here the reversibility of phosphorylation of insulin receptors either partially purified by lectin chromatography, or highly purified by specific immunoprecipitation with anti-receptor antibodies. We found that the beta subunit of partially purified insulin receptors was rapidly dephosphorylated (t 1/2 = 15 min). In contrast, the level of phosphorylation of immunoprecipitated receptors remained unchanged for up to 4 hours at 37 degrees C. However, cytosolic phosphatases, which are inhibited by vanadate, were able to induce a complete dephosphorylation of immunoprecipitated receptors. These results show that 1. phosphorylation of insulin receptors is reversible; and 2. no phosphatase activity is contained in the insulin receptor structure itself.