Involvement of lysine residues in the binding of ovine chorionic somatomammotropin to lactogenic and somatotropic receptors

Abstract

The biological activities of several ovine chorionic somatomammotropin (oCS) derivatives obtained by chemical modification of the lysine residues were studied by radioreceptor assays using rabbit mammary homogenates (lactogenic activity, L.A.) and liver homogenates (somatotropic activity, S.A.). Even if the control treatment with BHI markedly decreased the L.A., it was clear that methylation mainly affected the S.A. and that ethylation reduced both activities. Guanidination inactivated almost completely both activities and acetimidination at a very low degree (3 of 14 lysines) led to less than 50% of both activities. These results show the involvement of lysine residues in the interaction of oCS with lactogenic and somatotropic receptors. Ovine chorionic somatomammotropin Prolactin Growth hormone Lysine residue Receptor

Growth hormones. II. Structure—function relationships

“…lodination of 3 tyrosine residues of bGH does not interfere with the structure of this hormone, which exhibits a similar circular dichroism spectrum and does not modify its activity for somatotropic sites . Biscoglio de Jimenez Bonino et al (1979) have observed a 50% reduction in n vivo in the bGH growth activity after trinitrophenylation of lysines 181, 145, 70, 113, 172 and 168 (Chene et aL, 1984;Martal e t al., 1985). They showed that whatever the degree and kind of chemical modification, lysine residues participate in the hormone-hepatic receptor interaction.…”