Design and synthesis of a novel biotinylated photoreactive insulin for receptor analysis

B1-(4-Azido-salicyloyl)-[B1-biocytin,B2-lysine]insulin was synthesized by double Edman degradation of A1,B29-Msc2-insulin and stepwise acylation at the N-terminus of the B-chain. This derivative is homogeneous in RP-HPLC and has a biological in vitro activity of 20% and receptor binding of 15%, relative to insulin. Radioiodination and HPLC gave the B1-labelled 125I-derivative (I) as well as the 4 isomers with 125I-labelled tyrosine (A14, A19, B16, B26). UV-induced crosslinking of I with insulin receptors led to specific labelling of the alpha-subunit (Mr 130,000). The peptide bond LysB2-AspB3 is completely cleavable by trypsin (EC 3.4.21.4). I is thus a new tool for the analysis of the hormone-binding region by making possible the isolation of tryptic, biotinylated receptor fragments labelled by the dipeptide 125I-4-azidosalicyloyl-biocytinyl-Lys.