Antipeptide antibodies toward the extracellular domain of insulin receptor beta-subunit

In order to investigate structure and function of β-subunit extracellular portion, four polyclonal antibodies (AP1, AP2, AP3 and AP4) toward peptides comprised in this region were generated. None of them recognizes native human and rat insulin receptor both in vitro and in whole cells. Two antibodies, AP1 and AP2, immunoprecipitate isolated (DTT-reduced) human β-subunits and bind to human IM-9 cell after α-subunit tryptic cleavage. Only AP1 recognizes rat β-subunit both in vitro and in trypsin treated rat FAO cells. These findings suggest that: (i) the extracellular portion of the insulin receptor β-subunit is partially covered by the α-subunit in human and rat native insulin receptors; (ii) human and rat β-subunit extracellular domains are different, at least in the amino acid sequence corresponding to residues 785-796 of the human insulin receptor.