Characterization of the chicken muscle insulin receptor

Insulin receptors are present in chicken skeletal muscle. Crude membrane preparations demonstrated specific ¹²⁵I-insulin binding. The nonspecific binding was high (36-55% of total binding) and slightly lower affinity receptors were found than are typically observed for crude membrane insulin binding in other chicken tissues. Affinity crosslinking of ¹²⁵I-insulin to crude membranes revealed insulin receptor α-subunits of M_r 128K, intermediate between those of liver (134K) and brain (124K). When solubilized and partially purified on wheat germ agglutinin (WGA) affinity columns, chicken muscle insulin receptors exhibited typical high affinity binding, with ∼10^-10 M unlabeled insulin producing 50% inhibition of the specific ¹²⁵I-insulin binding. WGA purified chicken muscle insulin receptors also exhibited insulin-stimulated autophosphorylation of the β-subunit, which appeared as phosphorylated bands of 92- and 81K. Both bands were immunoprecipitated by anti-receptor antiserum (B₁₀). WGA purified membranes also demonstrated dose-dependent insulin-stimulated phosphorylation of the exogenous substrate poly(Glu, Tyr)4:1. However, unlike chicken liver, chicken muscle insulin receptor number and tyrosine kinase activity were unaltered by 48 hr of fasting or 48 hr of fasting and 24 hr of refeeding. Thus, despite the presence of insulin receptors in chicken muscle showing normal coupling to receptor tyrosine kinase activity, nutritional alterations modulate these parameters in a tissue-specific manner in chickens.