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Effects of Removal of Carboxy-Terminal Extension from Equine Luteinizing Hormone (LH) β-Subunit on LH and Follicle-Stimulating Hormone Receptor-Binding Activities and LH Steroidogenic Activity in Rat Testicular Leydig Cells*

1989; Oxford University Press; Volume: 124; Issue: 1 Linguagem: Inglês

10.1210/endo-124-1-379

1945-7170

George R. Bousfield, Wan-Kyng Liu, Darrell N. Ward,

Hypothalamic control of reproductive hormones

Residues 121–149 of equine LHβ (eLHβ) were removed by a simple mild acid treatment procedure. The modified eLHβ, des(121–149)eLHβ, was isolated by gel permeation chromatography on Sephacryl S-200. Recombination of des(121–149)eLHβ with eLHα and ovine LHα (oLHα) produced LH derivatives as efficiently as recombination with native eLHβ. In rat testicular LH radioligand assay systems employed in this study the potencies of the resulting LH preparations were, in order of decreasing potency: des(121–149)eLHβ:eLHα hybrid > eLH > eLHα + β > oLH > des(121–149)eLHβ:oLHα > oLHα + eLHβ (1:0.82:0.67:0.15:0.02:0.006, eLH tracer; 1:0.88:0.67:0.21:0.02:0.006, hCG tracer). In a horse testicular LH radioligand assay with eLH tracer, only the equine LH derivatives were active, and the order of potencies was the same: des(121–149)eLHβ:eLHα hybrid > eLH > eLHα + β (1:0.58:0.46). In a rat testicular Leydig cell steroidogenesis assay, eLH was the most active preparation, but the relative potencies of the other preparations remained unchanged: eLH > des(121–149)eLHβ:eLHα > eLHα + P > oLH > des(121–149)eLHβ:eLHα > oLHa + eLHβ (1:0.61:0.55:0.27:0.004:0.003). We have previously reported that the hybrid consisting of native eLHβ and oLHα was inactive (<1%) in LH receptor and steroidogenesis assays. The data reported herein confirm this observation and demonstrate that the absence of LH activity in eLHβ:oLHα cannot be attributed to the C-terminal extension on eLHβ, since the des(121–149)eLHβ:oLHα hybrid LH is also inactive. Examination of the intrinsic FSH activity of eLH in both rat and chicken testicular FSH radioligand assays produced the following results; eLH, recombined eLH subunits, and des(121–149)eLHβ:eLHα were all of the same potency (13% and 0.9% as active as eFSH in rats and chickens, respectively). We conclude that the C-terminal extension on eLH and eCG β- subunits is not involved in subunit association, LH receptor binding, or FSH receptor binding. The derivative des(121–149)eLHβ:eLHα provides a model compound that may be useful in determining the role, if any, of the glycoprotein hormone Cterminal extension that appears to have arisen independently at least twice in mammalian evolution. (Endocrinology124: 379–387,1989)