Involvement of lysine residues in the binding of hGH and bGH to somatotropic receptors.

The biological activities of human (hGH) and bovine (bGH) growth hormone derivatives obtained by chemical modification of the lysine residues were studied by radioreceptor assays using rabbit liver homogenates for somatotropic activity (SA). Control treatment with BH4 had a very slight effect on the SA, whereas the methylation and ethylation drastically reduced the activity of both hormones. Guanidination of these hormones and even acetimidination at a lower rate are accompanied by a considerable loss of biological activity. These results show the involvement of lysine residues in the interaction of hGH and bGH with somatotropic receptors. The structure-function relationship of these molecules is discussed, suggesting that the lysine or arginine residues in positions 41, 64, 70 and 115 might be particularly implicated.