Abstract
Insulin action in intact adipocytes leads to a rapid increase in the concentration of receptors for insulin-like growth factor (IGF) II on the adipocyte cell surface, and to a decrease in the [32P]phosphate content of these receptors on the plasma membrane [Corvera & Czech (1985) Proc. Natl. Acad. Sci. U.S.A. 82. 7314-7318]. It has been previously shown that the receptor for IGF-II can be phosphorylated on tyrosine residues by a kinase activity which is expressed in isolated adipocyte plasma membranes. It is now shown that IGF-II-receptor phosphorylation in vitro, in plasma membranes derived from insulin-treated cells, is markedly decreased compared with the phosphorylation of the receptor in membranes from control cells. This effect of insulin cannot be attributed to an increase in the activity of phosphotyrosyl phosphatase in the membranes. The tyrosine kinase that catalyses the phosphorylation of IGF-II receptors is associated with a fraction of the plasma membrane which is insoluble in Triton X-100. Removal of the Triton X-100-soluble components of the membrane markedly enhances receptor phosphorylation. Moreover, the expression of the inhibitory effect of insulin requires the presence of one or several Triton X-100-soluble components of the plasma membrane.