title: Glucagon amino groups. Evaluation of modifications leading to antagonism and agonism.
abstract: Using native glucagon and [12-homoarginine]glucagon (analogue A), prepared in high yield and purity by new procedures, we have synthesized the following glucagon analogues by semisynthetic methods: [1-deshistidine][12-homoarginine]glucagon (analogue B); N alpha-carbamoylglucagon (analogue C); N alpha, N epsilon-dicarbamoylglucagon (analogue D); [1-N alpha-carbamoylhistidine, 12-N epsilon-trinitrophenyllsyine]glucagon (analogue II); [1-deshistidine] [2-N alpha-trinitrophenylserine, 12-homoarginine]glucagon (analogue III); and [1-N alpha-trinitrophenylhistidine, 12-homoarginine]glucagon (analogue IV). The introduction of hydrophylic groups at the alpha- and epsilon-amino positions of glucagon results in a reduction in potency. The alpha-position is also involved in biological activity. Carbamylation of the alpha-position results in a partial agonist (analogues C and D). The introduction of hydrophobic groups and the neutralization of the positive charge at the alpha- and epsilon-amino positions result in glucagon antagonists (analogues II, III, and IV). [1-N alpha-Trinitrophenylhistidine, 12-homoarginine]glucagon (analogue IV) is the most potent inhibitor tested. Based on its competitive inhibitory action, this analogue appears to have about one-third the affinity of glucagon for the receptor site. These modifications at the epsilon-amino position cause an increase in the secondary structure of the peptide (as shown by circular dichroism studies) which may be related to their biological activities.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D002942:Circular Dichroism; D004789:Enzyme Activation; D005934:Glucagon / Q000031:analogs & derivatives* / Q000494:pharmacology*; D008099:Liver / Q000201:enzymology; D008722:Methods; D013329:Structure-Activity Relationship
chemical_list: D000596:Amino Acids; D005934:Glucagon; D000262:Adenylyl Cyclases