The effects of the trinitrophenylation of the amino groups of glucagon on its conformational properties and on its ability to activate rat liver adenylyl cyclase

Abstract

Trinitrophenyl groups have been specifically introduced into the α- and/or the ε-NH 2 groups of glucagon by reaction with trinitrobenzenesulfonic acid. Introduction of this group into the ε-NH 2 position of the hormone leads to an apparant increase in the helical content as measured by circular dichroism, while substitution on the α-NH 2 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 p K 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 cyclase of rat liver. By comparison with previously reported results, this demonstrates that the effect of chemical modification of the amino group on the biological activity of glucagon depends critically on the group which is introduced.