Carboxyl group modification in glucagon

Glycineamide reacts quantitatively with the four carboxyl groups of glucagon in the presence of 1-ethyl-3-(3-dimethylaminopropylcarbodiimide) and 7 M guanidine hydrochloride. The product of this reaction has greatly enhanced solubility in water but still aggregates as shown by the concentration dependence of the circular dichroism and ultracentrifuge studies. The circular dichroism at pH 2.8 resembles that of glucagon. Blockage of the carboxyl groups by glycineamide or methanol results in the loss of the ability of the peptide to stimulate adenyl cyclase.