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Arch Biochem Biophys. 1983 Sep;225(2):490-9.

Use of alpha- and beta-subunit specific antibodies in studying interaction of hCG with Leydig cell receptors.


Antisera (a/s) raised to individual alpha- and beta-subunits of human chorionic gonadotropin (hCG) have been characterized for specificity using immunoaffinity procedures and used to study the disposition of the two subunits when intact hCG is complexed with luteinizing hormone (LH) receptor of the Leydig cells. Three kinds of experiments were done. (a) The ability of the preformed hormone-antibody (H-Ab) complex to bind to receptor and stimulate a response; (b) the ability of the a/s to dissociate hCG from its complex with the receptor and thereby terminate response; and (c) the ability of the premixed antibody and receptor to compete for binding of labeled hCG. Although the subunit specific a/s used here were equipotent in binding hCG (capacity to bind and Ka being very similar), their behavior once the receptor preparation or Leydig cell is introduced into the system was drastically different. The beta-subunit antibody relative to the alpha-subunit antibody, appeared to be poorly effective in preventing hCG from either binding to the receptor or inhibiting the continuation of response. The results suggest that hCG upon interaction with the receptor loses the determinants specific to the beta-region more rapidly compared to those specific to the alpha-region suggesting thereby that the initial interaction of hCG with the receptor should be occurring through sites in the beta-subunit. Although the alpha-subunit portion of the hCG molecule is available for binding to the antibody for a relatively longer time, the biological response of the cell seems very sensitive to such binding with the antibody as it invariably results in loss of response.(ABSTRACT TRUNCATED AT 400 WORDS).

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