Binding of bovine growth hormone to bovine liver membranes

The binding of [125I]bGH and [125I]hGH to bovine liver membranes is compared to characterize the somatotrophic hormone-receptor interaction. [125I]bGH binding exhibits higher nonspecific binding than [125I]hGH while the time-course of binding and displacement with unlabeled GH are similar. Divalent and monovalent cations enhance [125I]hGH binding with well-defined peaks of binding at specific cation concentrations. Monovalent cations do not enhance [125I]bGH binding at concentrations of 100 mM while divalent cations enhance binding over a range of cation concentration (4-80 mM). The binding of [125I]bGH is dependent upon the presence of divalent cations, with minimal effect of pH upon binding in the absence of calcium. Scatchard plots of bGH and hGH binding data indicate at least two binding sites. We conclude that somatotrophic GH exhibits unique and distinguishing characteristics of binding. The characteristics of hGH binding to the bovine liver membranes suggest that its binding may differ from bGH binding to its homologous receptor.