US EPA

7493795 

Journal Article 

Physical Characterization of S-Methylglucagon and Quantitation of Carbamino Adduct Formation 

Rothgeb, TM; England, RD; Jones, BN; Gurd, RS 

1978 

Yes 

Biochemistry
ISSN: 0006-2960
EISSN: 1520-4995 

17 

21 

4564-4571 

English 

10.1021/bi00614a031 

Methylation of the single methionine residue at position 27 of glucagon yields a highly soluble sulfonium derivative, S-methylglucagon. The increased solubility of S-methylglucagon makes natural abundance l3C nuclear magnetic resonance studies accessible. These studies have resulted in the determination of pKt values for the proton dissociations of the histidine-1 α-amino and imidazole functional groups of 7.23 and 5.32, respectively. Equilibration of S-methylglucagon with l3CO2 yields a carbamino adduct which is identified and quantitated. The pKc value corresponding to the formation constant of the carbamate with the peptide α-amino group is 4.66. These values of pK7 and pKc, which define the extent of carbamino adduct formation for all values of pH and pCO2, imply that under normal physiological conditions the mole fraction of carbamate is near 0.35 and that this mole fraction varies significantly over the physiologically important range of extracellular pH and pCCO2 values. Since the «-amino group of the hormone is necessary for apparent biological activity, the reversible carbamate formation which will occur to a variable extent in vivo may alter the biological effectiveness of the peptide hormone. Justification for the use of S-methylglucagon as a model for native glucagon comes from nuclear magnetic resonance and circular dichroism evidence, which indicates that the two peptides have similar secondary structures at dilute peptide concentrations and that the structure of S-methylglucagon appears to be independent of peptide concentration in contrast to the native hormone. This is consistent with S-methylglucagon resisting intermolecular association, thereby making this derivative an excellent model for the native hormone in its predominant physiological form. © 1978, American Chemical Society. All rights reserved. 

glucagon; animal experiment; s methylglucagon; swine; Circular Dichroism; Comparative Study; Glucagon; Kinetics; Magnetic Resonance Spectroscopy; Methionine; Methylation; Potentiometry; Protein Conformation; Support, U.S. Gov't, P.H.S.