Comparison of insulin-like growth factor I receptor and insulin receptor purified from human placental membranes.
Insulin-like growth factor (IGF)-I receptor purified from human placental membranes as previously described (LeBon, T. R., Jacobs, S., Cuatrecasas, P., Kathuria, S., and Fujita-Yamaguchi, Y. (1986) J. Biol. Chem. 261, 7685-7689) was characterized. The IGF-I receptor was similar to the insulin receptor with respect to subunit structure (beta-alpha-alpha-beta), apparent sizes of deglycosylated alpha (Mr = approximately 88,000) and beta (Mr = approximately 67,000) subunits, and amino acid composition of the subunits. Monoclonal antibody specific to each receptor recognized its own receptor whereas polyclonal anti-human insulin receptor antibody cross-reacted with the IGF-I receptor, indicating that the receptors share one or more antigenic sites. Further characterization of the purified IGF-I receptor tyrosine-protein kinase activity indicated that by analogy with the insulin receptor the monomeric alpha beta form of the IGF-I receptor appears to have higher kinase activity than the intact receptor in the alpha 2 beta 2 form. The most significant difference between the two receptors was found in the N-terminal amino acid sequences of their alpha subunits, which apparently show 60% identity. The IGF-I receptor alpha subunit lacks residues corresponding to the N-terminal 4 amino acids of the insulin receptor alpha subunit. These results provide the first direct proof that the IGF-I receptor is a molecule distinct from the insulin receptor despite numerous similarities.
D000595:Amino Acid Sequence; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D004229:Dithiothreitol / Q000494:pharmacology; D005260:Female; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011972:Receptor, Insulin / Q000302:isolation & purification / Q000378:metabolism*; D017451:Receptors, Somatomedin
D046911:Macromolecular Substances; D017451:Receptors, Somatomedin; D011972:Receptor, Insulin; D004229:Dithiothreitol