title: Characterization of human somatotropin binding to detergent-solubilized lactogenic receptors from rat liver.
abstract: Lactogenic receptors from rat liver microsomal fraction ('microsomes') were extracted by treatment with 1% (w/v) Triton X-100. Triton X-100 exerts an inhibitory effect on both the binding reaction and the separation of the free hormone from the complex. The association and dissociation of 125I-labelled human somatotropin are time- and temperature-dependent processes. The association rate constant, k1, is 6.7 x 10(6) mol . litre-1 . min-1 at 25 decrees C, and the dissociation rate constant, k-1, is 1.1 x 10(-3) min-1 at 25 degrees C. Scatchard analysis of saturation data reveals the existence of a single class of receptors and that solubilization leads to a slight decrease in affinity and a sharp increase in binding capacity. The dissociation constant, Kd, of the solubilized preparation is 0.22 nM and the binding capacity 2900 fmol/mg of protein. Similar results were obtained from competition experiments. Binding of 125I-labelled human somatotropin to the solubilized receptors is specifically inhibited by hormones with lactogenic activity. Incubation of the solubilized preparation with trypsin resulted in an 80% decrease in binding activity. The solubilized form of the receptor has a slightly increased sensitivity to the inactivation by trypsin, heat and extremes of pH, with respect to the membrane-bound form.
mesh_terms: D000818:Animals; D005260:Female; D013006:Growth Hormone / Q000378:metabolism*; D006728:Hormones / Q000494:pharmacology; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008862:Microsomes, Liver / Q000032:analysis*; D011092:Polyethylene Glycols / Q000494:pharmacology; D051381:Rats; D011956:Receptors, Cell Surface / Q000302:isolation & purification / Q000378:metabolism*; D018000:Receptors, Peptide; D012995:Solubility; D014357:Trypsin / Q000494:pharmacology
chemical_list: D006728:Hormones; D011956:Receptors, Cell Surface; D018000:Receptors, Peptide; C028202:placental lactogen receptor; D011092:Polyethylene Glycols; D013006:Growth Hormone; D014357:Trypsin