Functional groups in ovine luteinizing hormone and their receptor site interactions-a chemical study

Structure and structure-function relationships in glycoprotein hormones

Relationships between the sequences of thyrotropin (thyroid-stimulating hormone, TSH), lutropin (luteinizing hormone, LH), human choriogonadotropin (chorionic gonadotropin, hCG) and follitropin (follicle-stimulating hormone, FSH) are now well established. Each beta-subunit contains six disulphide bonds and considerable homology is seen when all four linear sequences are aligned with half-cystine residues in juxtaposition. Major questions about the tertiary structures of the subunits and their interactions to form active hormone remain. Determination of the disulphide bridges in both alpha- and beta-subunits has not yielded to usual methods and conflicting data about the alpha-subunit have been reported. Partial reduction of the beta-subunits of LH and TSH with subsequent labelling of the cysteines formed has shown that a single bond is first reduced. This bond is between positions 93 and 100 in LH-beta and the corresponding positions 88-95 in TSH-beta. Thus, as would be expected from the fact that interhormone hybrids can be made with the common alpha-subunits, the chemical data, though still limited, indicate similar tertiary structures for the different beta-subunits. To investigate whether other useful intermediates can be obtained after partial reduction, we have studied reduction and derivative formation in various conditions. Intact LH is more resistant to reduction than either its alpha- or beta-subunit but no intermediates have been observed which are not present after partial reduction of individual subunits. Preliminary experiments on the reoxidation of fully reduced alpha-subunit show that the reoxidized material will recombine with native beta-subunits to yield biologically active TSH or LH. Studies from this and other laboratories on chemical modifications of several amino acid residues of glycoprotein hormones and their subunits are also summarized.

Monoclonal antibodies against human chorionic gonadotropin (hCG): II. Affinity and ability to neutralize the biological activity of hCG

Monoclonal antibodies (MCA) against hCG have been characterized with regard to their affinity and their ability to neutralize the biological activity of hCG in vivo. The production and specificities of these reagents were described in the preceding paper of this series. Equilibrium association constants (Ka) of the MCA, determined by radioimmunological saturation assays, ranged from less than 1 X 10(8)M-1 up to 3.7 X 10(9)M-1 whereas values for conventional polyclonal antisera against hCG ranged from 8.9 X 10(9)M-1 to 1.8 X 10(10)M-1. The ability of MCA to neutralize the biological activity of hCG was tested in a rat bioassay in vivo; 9 of 13 different MCA preparations tested could neutralize hCG. Surprisingly, this property did not correlate with affinity or specificity, and was not restricted to those MCA recognizing the hormone specific beta-subunit. It could be demonstrated that determinants on each individual subunit as well as epitopes formed by both subunits are involved in the expression of the biological activity of hCG.