title: Preparation of 2-thioltryptophan-glucagon and (tryptophan-S-glucagon)2. Differences in binding to the glucagon receptor in the hepatic adenylate cyclase system.
abstract: The synthesis of 2-thioltryptophan-glucagon is described. Oxidation of this compound gives the dimer (Trp-S-glucagon)2. Both monomer and dimer are equi-potent on a molar basis with native glucagon as activators of adenylate cyclase in hepatic plasma membranes. However, from the ability to compete with 125I-glucagon for binding at the glucagon receptor, the dimer has one-fourth the binding affinity for the receptor as does native glucagon, 2-thiol-Trp-glucagon, and Trp-(2,4-dinitrophenylsulfenyl)-glucagon which have equal affinities for the receptor. Addition of GTP, which converts the receptor from a tight-binding to a lower affinity form and which activates adenylate cyclase in the presence of glucagon, allows (Trp-S-glucagon)2 to bind equally with native glucagon and the other thiol derivatives of the hormone. This effect of GTP on the binding of the glucagon dimer and the uses of 2-thiol-Trp-glucagon in the semisynthesis of new glucagon derivatives are discussed.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D002942:Circular Dichroism; D004789:Enzyme Activation; D005934:Glucagon / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000378:metabolism / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D011487:Protein Conformation; D051381:Rats; D013056:Spectrophotometry, Ultraviolet; D013329:Structure-Activity Relationship; D014364:Tryptophan / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D000596:Amino Acids; C027520:2-thioltryptophan; C027521:glucagon, thiol-Trp(2); C027523:S-glucagon dimer, Trp-; D014364:Tryptophan; D005934:Glucagon; D000262:Adenylyl Cyclases