Insulin receptors in rat brain: insulin stimulates phosphorylation of its receptor β‐subunit

Abstract

In rat brain cortex synaptosomes insulin stimulated the phosphorylation of its own receptor β-subunit (94 kDa) as identified by immunoprecipitation with anti-insulin or anti-receptor antiserum. The receptor α-subunit (115 kDa) was characterized by specific labeling with 125I-labeled photoreactive insulin. These observations indicate that: (i) insulin receptors in brain are composed of α-subunits which bind insulin, and β-subunits, the phosphorylation of which can be stimulated by insulin; (ii) the size of α-subunits in brain is significantly smaller than in other tissues (115 vs 130 kDa), whereas β-subunits (94 kDa) are identical. We suggest that brain insulin receptors represent a subtype regarding their binding function, whereas their enzyme function is more conserved