Studies on the Molecular Architecture and the Composition of the GH Receptor from Rabbit Liver,

Abstract

Binding of human growth hormone (hGH) to plasma membranes from rabbit liver is slightly inhibited by β-mercaptoethanol (β-MSH), dithiothreitol (DTT), and N-ethylmaleimide (NEM). L-Cys has a marked stimulating effect at 20 mM. Pretreatment of plasma membranes with phospholipase A2-C, and D does not influence hGH binding. In the presence of DNase and RNase a slight but distinct elevation of hormone binding is seen. HGH-receptor interaction is totally abolished in the presence of trypsin. This effect is inhibited by trasylol and trypsin inhibitor from soya bean. Neuraminidase has no effect on hGH binding, whereas α or β-galactosidase lead to a complete abolition of hGH-receptor interaction. Analysis of the receptor complex in the presence and absence of hGH leads to at least two distinct polypeptide chains with molecular weights 68 000 and 76 000 daltons on the SDS-gel electrophoresis. The significance of a peptide with 56 000 dalton is not clear. It is concluded that -SH groups and phospholipids are not involved in hGH binding. The effect of nucleases is not understood. Within the hormone recognition area peptide chains carrying galactose residues in α and β-glycosidic bonding are essential for hGH-receptor interaction. Two or three proteins seem to represent integral constituents of the hGH receptor complex.