Differential properties of human chorionic gonadotrophin and human luteinizing hormone binding to plasma membranes of bovine corpora lutea.

Plasma membranes of bovine corpora lutea contain common receptor sites for [125I]human chorionic gonadotrophin (hCG) and [125I]human luteinizing hormone (hLH) to which hLH binds with 4-fold lower affinity than hCG. The presence of additional sites for hLH was indicated by the lack of saturation of [125I]hLH binding as compared to [125]hCG and lower degree of inhibition of binding by 830 pM of unlabelled hCG, when [125I]hLH instead of [125I]hCG was used. Differences in [125I]hCG and [125I]hLH binding were observed by exposing receptors to increasing temperatures and pHs and by pre-treating membranes with dimethyl sulphoxide, Triton X-100, various enzymes and protein reagents. The above differences can only be reconciled by differential responses of common hCGhLH sites and additional sites for hLH.