Specific modification of carboxyl-groups in bovine growth hormone by a soluble carbodiimide and glycinemethylester.

The reactivity of the carboxyl groups in bovine growth hormone was studied by reaction with 1-ethyl-3(3-dimethylaminopropyl) carbodiimide in the presence of an excess of glycinemethylester. Localization in the molecule of the various kinetically distinguishable carboxyl groups was achieved. Highest reactivity was found in carboxyl groups 30, 125, 127 and 128. These residues were followed, as to reactivity, by a set including carboxyl groups 65, 105, 151, 152, 185 and 190. Modification of approximately one fifth of the carboxyl groups in bovine growth hormone led to an important decrease in its growth promoting activity and capacity to compete with 125I-labeled growth hormone for rat liver binding sites. Demethoxylation restored most of the original biological activity.