Hormone glycosylation required for lutropin receptor recognition in sheep testis.

The high affinity binding sites for ovine pituitary lutropin (oLH) present in DLS-1 sheep testis recognized only the fully glycosylated ovine or bovine hormone (bLH) in receptor binding assays using 125I-labeled oLH. Chemically deglycosylated (DG-) oLH or bLH which were fully active with other lutropin receptors (rat/pig) were completely inert in the DLS-1 receptor assay. In the same membranes, the FSH (follitropin) receptor reacted well with both glycosylated FSH and DG-oFSH. In recombination studies, lutropin formed by glycosylated native alpha- and beta-subunits of the hormone was fully active but when one of the subunits was in the deglycosylated form, receptor binding activity was greatly reduced. The presence of glycosylated alpha-subunit in the recombined hormone gave rise to 5x more activity than DG-alpha + beta. All these preparations were fully active in the rat/pig receptor assays for LH. These results demonstrate that lutropin hormone glycosylation is essential for optimum receptor recognition in the sheep testis, further emphasizing the importance of correct glycosylation in oLH alpha hormone function.