Insulin receptor dephosphorylation in permeabilized adipocytes is inhibitable by manganese and independent of receptor kinase activity.

Autophosphorylation of insulin receptors in digitonin-permeabilized rat adipocytes increased progressively as manganese concentrations were increased. In contrast, the percent dephosphorylation of insulin receptors, when examined by chasing the [gamma-32P]ATP with unlabeled ATP, decreased at the higher manganese concentrations. Removing manganese with EGTA increased the extent of dephosphorylation by 50 to 75%. When added only at the chase, manganese but not insulin (10(-7) M) inhibited dephosphorylation. Removal of both magnesium and manganese with EDTA completely inhibited receptor autophosphorylation. However, EDTA potentiated dephosphorylation similar to EGTA when added after 2 min of phosphorylation. Thus, a dephosphorylation reaction involving the membrane-associated insulin receptor is inhibited by manganese and is independent of the receptor kinase activity. This work suggests that manganese increases net autophosphorylation of the receptor not only by enhancing kinase activity but by inhibiting receptor dephosphorylation.