Gonadotropin Receptor of a Mouse Luteoma: Interactions with Luteinizing Hormone (LH) and its α and β Subunits1

Open Access
Publisher Website
Google Scholar
Abstract
Homogenates of a transplantable pituitary-dependent functional mouse luteoma bind 123I-human luteinizing hormone (125I-hLH). Binding of 125I-hLH is reduced in the presence of ovine LH, bovine LH, and human chorionic gonadotropin (hCG). Other peptide hormones tested do not reduce (GH, ACTH, and prolactin), or reduce 125I-hLH binding (FSH and TSH) only to an extent consistent with the probable LH contamination of each preparation. Assay ranges for bovine LH and hCG are 0.1–10 μg and 50 mIU-1 IU, respectively. An apparent dissociation constant (Kd) of ∼4nM was observed using chloramine T-iodinated and lactoperoxidase-iodinated 125I-hLH in the luteoma hLH receptor. Increasing amounts of bovine LH and bovine a and β subunits progressively decrease 125I-hLH bound to the luteoma LH receptor. The low potency of the LH subunits in reducing 125I-hLH binding can probably be attributed to residual contamination of these preparations with native hormone. Lactoperoxidase 125I-labeled subunits interact in the luteoma LH receptor only to an extent consistent with their possible residual contamination with native hormone. These observations suggest that the structural requirements for binding to the luteoma LH receptor demand a polypeptide conformation found in the native hormone. Neither subunit alone appears to possess this conformation. This luteoma LH receptor system offers a specific, convenient, rapid, and sensitive biologic tool for studying the interactions between LH and its receptor and substances which compete with LH for the LH receptor.

This publication has 0 references indexed in Scilit: