Involvement of lysine residues in the binding of ovine prolactin and human growth hormone to lactogenic receptors.

The lactogenic activity (L.A.) of oPRL and hGH derivatives obtained by chemical modifications of lysine residues was studied by radioreceptor assay. Control treatment with borohydride had a slight effect on the L.A. of hGH but drastically reduced the oPRL activity; this latter was preserved in the presence of iodoacetamide. Methylation, ethylation, guanidination and acetimidination affected the L.A. of both hormones as a function of the degree of modification. The structure-binding relationships to the lactogenic receptors are discussed, suggesting that the lysine or arginine residues in homologous positions 42, 51, 73, 128, 146 of oPRL and 47, 50, 73, 128, 147 of hGH might be particularly involved.