Receptor binding and adenylate cyclase activities of glucagon analogs modified in the N-terminal region

Abstract

In this study, we determined the ability of four N-terminally modified derivatives of glucagon, [3-Me-His1,Arg12]-, [Phe1,Arg12]-, [D-Ala4,Arg12]-, and [D-Phe4]glucagon, to compete with 125I-glucagon for binding sites specific for glucagon in hepatic plasma membranes and to activate the hepatic adenylate cyclase system, the second step involved in producing many of the physiological effects of glucagon. Relative to the native hormone, [3-Me-His1,Arg12]glucagon binds approximately twofold greater to hepatic plasma membranes but is fivefold less potent in the adenylate cyclase assay. [Phe1,Arg12]glucagon binds threefold weaker and is also approximately fivefold less potent in adenylate cyclase activity. In addition, both analogues are partial agonists with respect to adenylate cyclase. These results support the critical role of the N-terminal histidine residue in eliciting maximal transduction of the hormonal message. [D-Ala4,Arg12]glucagon and [D-Phe4]glucagon, analogues designed to examine the possible importance of a beta-bend conformation in the N-terminal region of glucagon for binding and biological activities, have binding potencies relative to glucagon of 31% and 69%, respectively. [D-Ala4,Arg12]glucagon is a partial agonist in the adenylate cyclase assay system having a fourfold reduction in potency, while the [D-Phe4] derivative is a full agonist essentially equipotent with the native hormone. These results do not necessarily support the role of an N-terminal beta-bend in glucagon receptor recognition. With respect to in vivo glycogenolysis activities, all of the analogues have previously been reported to be full agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucagon receptors

“…Vol. 65,2008 cagon, a GR agonist of enhanced biological potency [160], GR endocytosis, Gsa shift and activation of endosomal adenylyl cyclase are of higher magnitude and of longer duration confirming that glucagon signal transduction may occur in vivo at the locus of endosomal apparatus [151].…”

“…In liver and other tissues that express the GR, the concentrations of glucagon required for half-maximal and maximal effects are in the range of 2-4 nM and 30-100 nM, respectively [4,[63][64][65][66][67]. However, in both liver membranes [68] and hepatocytes [14], as well as in intact liver following glucagon injection (Fig.…”

“…Vol. 65,2008 Review Article logical activity and is a modulator of the action of glucagon, the mother molecule. At picomolar concentrations, miniglucagon inhibits the hepatic plasma membrane Ca 2+ pump without interfering with the adenylyl cyclase activity [126].…”

Glucagon antagonists for the treatment of Type 2 diabetes

“…Based on his findings and those of Merrifield [11], it is clear why many of the present glucagon analogues in the literature have either lacked the His 1 amino acid or contained a modified histamine residue at the 1-position such as 3-CH 3 His 1 [12].…”

Binding of [125I]‐endothelin‐1 to rat cerebellar homogenates and its interactions with some analogues

“…[1 251]-endothelin-J Human endothelin-1 (1 nmol; Peptide Institute, Osaka, Japan) was iodinated by the method of McKee et al (1986) Synthesis of analogues of endothelin-J Analogues of endothelin-1 were synthesized by standard solidphase synthetic techniques using an automated peptide synthesizer employing Boc/Bzl chemistry (Merrifield, 1963;Stewart & Young, 1984) and t-butyloxycarbonyltryptophyl-4-(oxymethyl)phenylacetamidomethyl resin. The peptides were deprotected and removed from the resin with the two-step 'low-high' HF method (Tam et al, 1983).…”