ABSTRACT
The chemistry and physiological role(s) of the insulin-like growth factors (IGFs) and their receptors have been the subject of several reviews. It has turned out that the IGF-1 receptor has many characteristics in common with the insulin receptor, most strikingly its intrinsic protein-tyrosine kinase activity that is apparently lacking in the IGF-2 receptor. Within α subunit, a disulfide-rich region is common to insulin and IGF-1 receptors, and this region is postulated to comprise at least part of the ligand-recognizing domain. The sequence of this receptor domain probably reflects the requirement for a similar three-dimensional structure but a separate set of interacting ligand-receptor residues such that each receptor recognizes only its own specific ligand with high affinity. The mechanism by which transmembrane activation of the kinase occurs has not been elucidated for the IGF-1 receptor. Unfortunately, in neither of the above cases is there any information on how observed phosphoprotein may play a role in biological function.
