| Abstract: | The role of the Tyr10-Ser11-Lys12-Tyr13 region of glucagon in the binding interaction and activation of the glucagon receptor was investigated by means of the synthetic glucagon analogues Phe13]glucagonamide, Phe10]glucagonamide, Phe10]glucagon, Phe10,13]glucagon, Pro11]glucagon, Pro11,Gly12]glucagonamide, Ala11]glucagon, and Oac11-13]glucagonamide. These analogues were synthesized by solid-phase peptide synthesis on p-methylbenzhydrylamine or Merrifield resins with protected N alpha-tert-butyloxycarbonyl amino acids. Purification by dialysis, cation-exchange chromatography, gel filtration, and preparative reverse-phase high-performance liquid chromatography (HPLC) gave products that proved homogeneous by thin-layer chromatography and HPLC and on analysis by amino acid analysis, by sequencing, and by alpha-chymotryptic peptide mapping with HPLC. Biological activities were examined by measurement of the stimulation of liver plasma membrane adenylate cyclase and by specific displacement of 125I]glucagon from glucagon receptors. The results of these studies indicate that while the biological "message" region of glucagon is located elsewhere, the 10-13 region has multiple roles in the glucagon-glucagon receptor interaction: this region provides functional groups for direct binding interaction with the receptor, and this region interacts with the receptor in such a way as to allow the "transduction message" portion of glucagon to interact and activate the receptor. |
