The essential role of the imidazole group of glucagon in its biological function (original) (raw)
Related papers
Glucagon amino groups. Evaluation of modifications leading to antagonism and agonism
Journal of Biological Chemistry, 1980
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: [l-deshistidine][l2-homoarginine]glucagon (analogue B); N"carbamoylglucagon (analogue C); N",N'-dicarbamoylglucagon (analogue D); [l-Nu-carbamoylhistidine, 12-N"trinitrophenyllysine]glucagon (analogue II); [ldeshistidine] [2-Na-trinitrophenylserine, 12-homoargininelglucagon (analogue III); and [l-N"-trinitrophenylhistidine, 12-homoarginine]glucagon (analogue IV). The introduction of hydrophylic groups at the a-and €-amino positions of glucagon results in a reduction in potency. The a-position is also involved in biological activity. Carbamylation of the a-position results in a partial agonist (analogues C and D). The introduction of hydrophobic groups and the neutralization of the positive charge at the a-and eamino positions result in glucagon antagonists (analogues 11, 111, and IV). [l-N"-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 eamino 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.
Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology, 1982
Acylation of the a-and c-amino groups of histidine-1 and iysine-12 in glucagon with citraconic anhydride resulted in the formation of amide bonds which displayed different stabilities to hydrolysis under mild acid conditions. Treatment of N~"-dicitraconyi glucagon at pH 4.0 and room temperature regenerated the free c-amino group within 16 h, while the citraconyl-a-amino group was stable. N~-Citraconyl glucagon was purified by anion-exchange chromatography and was a weak partial agonist in stimulating adenylate cyclase in rat liver plasma membranes. The derivative exhibited 1% of the biological potency and 35-40% of the maximal stimulation of glucagon. Binding affinity to plasma membranes was also reduced, but not to as great an extent as adenylate cyclase activity. Removal of the a-citraconyl group by treatment with 10 mM HCI at 40°C restored full potency and stimulation to glucagon. These results suggest that the N-terminal histidine of glucagon is involved in both binding to plasma membranes and transduction of the signal to adenylate cyclase.
Effect of glucagon on alanine 2-oxoglutarate aminotransferase
Biochemical and Biophysical Research Communications, 1983
~A~n~2coxoglutarate aminotransferase activity in ~ouse li~e~v~gis stimulated by the intravenous injection of ~q~Ft~on.°:'The stimulation is abolished by pretreatment with actinomycin D indicating that the increased activity is probably due to new enzyme formation. Administration of dibutyryl cyclic AMP, isoproterenol, an activator of adenyl cyclase and theophylline, an inhibitor of phosphodiesterase also increases the enzyme activity suggesting the involvement of cyclic AMP in glucagon-mediated increase of enzyme activity. Gluconeogenesis from alanine (i) is stimulated by glucagon in the perfused liver (2,3) as well as in isolated hepatocytes (4,5). The transport of alanine across the plasma membrane is also stimulated by glucagon (6). The conversion of alanine to pyruvate, one of the precursors of gluconeogenesis, is catalysed by alanine 2-oxoglutarate aminotransferas~ (EC 2.6.1.2)~> (7). The activity of this enzyme has been reported to be i-~c~reased during starvation, treatment with glucocorticoids, feeding of high protein diet (8) and in alloxan-induced diabetes (9). The effect of glucagon on this enzyme in vivo has, however, not been reported. The mode of action of glucagOn is not clear. Previously we have reported that glucagon stimulates fructose 1,6-bisphosphatase and that this stimulation is insensitive to actinomycin D or cycloheximide (i0). Claus et al (ii) have also reported that glucagon causes activation of fructose 1,6-bisphosphatase by phosphorylating the enzyme. On the other hand, administration of glucagon has been shown to stimulate *To whom correspondence should be sent.
Search for bioactive conformation of glucagon and development of potent glucagon antagonists
2000
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Biochimica et biophysica acta, 1975
Trinitrophenyl groups have been specifically introduced into the alpha- and/or the epsilon-NH2 groups of glucagon by reaction with trinitrobenzenesulfonic acid. Introduction of this group into the epsilon-NH2 position of the hormone leads to an apparant increase in the helical content as measured by circular dichroism, while substitution on the alpha-NH2 position causes little change in this property. The usefulness of the trinitrophenyl group for the study of intramolecular singlet excitation transfer from tryptophan is suggested. The pK and reactivity of the amino groups, as measured by the pH dependence of the rate of reaction with trinitrobenzenesulfonic acid, showed that the two amino groups of glucagon have similar properties to those of small model peptides. The trinitrophenyl-glucagon derivatives have little or no activity in stimulating adenylyl cylase of rat liver. By comparison with previously reported results, this demonstrates that the effect of chemical modifications o...
Journal of Biological Chemistry, 1986
The principal products derived from in vivo processing of anglerfish preproglucagon I1 were isolated and their structures determined. The structures were confirmed by a combination of automated Edman degradation, amino acid analysis, and fast atom bombardment mass spectrometry. The peptide corresponding to anglerfish preproglucagon 11-(22-49) (numbering from the amino terminus of preproglucagon) was isolated intact and defines the site of signal cleavage to be between Gln-21 and Met-22. Glucagon from the anglerfish preproglucagon gene I1 was found to correspond to preproglucagon 11-(52-80) (numbering from the amino terminus). Three forms of a glucagonlike peptide derived from preproglucagon I1 were also isolated. The structure of the longest form was consistent with the sequence of preproglucagon 11-(89-122) deduced from the cDNA,
Biochimica et Biophysica Acta (BBA) - General Subjects, 1974
The polypeptide hormone glucagon can react with the nucleophiles; glycinamide, taurine or ethylenediamine in the presence of 1-ethyl-3-(3-dimethylaminopropylcarbodiimide). The number of carboxyl groups which are modified depend on the concentration of guanidine hydrochloride in the reaction media. These results demonstrate an additional property which glucagon possesses in common with larger globular proteins and suggests that the hormone has a specific, folded structure in dilute aqueous solution. In the absence of guanidine hydrochloride only one taurine residue is incorporated into the terminal carboxyl group of the peptide. In 7 M guanidine hydrochloride all four of the carboxyl groups react with glycinamide or taurine while only two and a half residues of ethylenediamine are incorporated. All of these derivatives and glucagon have identical circular dichroism spectra in dilute aqueous solution. The taurine modified derivative has greatly enhanced solubility compared with glucagon but still associates to structures of higher helical content. Both of the taurine derivatives of glucagon have the ability to stimulate the adenyl cyclase of rat liver membranes but at concentrations several fold higher than is needed for the native hormone. It is suggested that each carboxyl group contributes to the binding of the hormone to the specific membrane receptor sites. * This work was presented in part at the Biochemistry/Biophysics 1974 Meeting. Minneapolis.