Regulation of enzyme activity by glucagon: increased hormonal activity of iodinated glucagon.

Abstract Iodination of glucagon enhanced its ability to activate adenyl cyclase in vitro , to elevate cyclic AMP levels in plasma in vivo , to induce two aminotransferases (PPT and TAT) in rat liver, and to stimulate amino acid uptake into rat liver in vivo . The degree of enhanced hormonal activity was proportional to the degree of iodination. Presumably the iodination of glucagon either confers on it greater intrinsic activity on the adenyl cyclase receptor or renders it less susceptible to degradation so that more glucagon molecules are available to act on the receptor.