Analysis of the human insulin receptor

The insulin derivative 4-azidosalicyloyl-[B1-biocytin-B2-lysine]insulin was used to photo-affinity-label the highly purified insulin receptor from human placenta. As shown by SDS-polyacrylamide gel electrophoresis, the 5 monoiodo isomers, with iodine in positions B1, B16, B26, A14 or A19, gave different labelling patterns. After complete tryptic digestion of the covalent receptor complex with 125I-Asa-[BctB1,LysB2]insulin, a stable fragment of 18 kDa was isolated, which was further purified by HPLC. This tryptic fragment of the intact receptor corresponds, according to HPLC, Tricin-SDS-PAGE and 2D-electrophoresis, to the similarly labelled sequenced domain of the receptor ectodomain (Fabry, M. et al. (1992) J. Biol. Chem. 267, 8950-8956). We thus conclude that insulin is bound to identical contact sites of native receptor and truncated ectodomain.