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Characterization of Human Lutropin Carboxyl- Terminus Isoforms¹

Département de Biologie Clinique, Institut Gustave-Roussy (J.P., P.R., F.T., D.B., J.-M.B.), 94805 Villejuif, France; Laboratoire d’Immunologie CNRS URA 1484, Faculté des Sciences Pharmaceutiques et Biologiques (D.B., J.-M.B.), 75006 Paris, France; and Service d’Histologie-Embryologie-Cytogénétique, CNRS URA2115, CHU Pitié-Salpétrière (M.K.), 75013 Paris, France

Address all correspondence and requests for reprints to: Pr. J. M. Bidart, Département de Biologie Clinique, Institut Gustave-Roussy, rue Camille Desmoulins, 94805 Villejuif, France. E-mail: bidart{at}igr.fr

Human lutropin (hLH) exhibits both carbohydrate and peptidic heterogeneities that affect its biological potency and the duration of its activity in vivo. Peptidic changes within the hLH ß-subunit are characterized as intrachain proteolytic nicking and carboxyl terminus heterogeneity. To date, the carboxyl terminus of hLHß appears to end at either position Gln¹¹⁴ or Gly¹¹⁷, as determined by sequencing of purified subunit. Furthermore, the complementary DNA for hLHß predicts a protein containing an additional peptidic stretch, which would make the ß-subunit 121 residues long. This extension may be responsible for the particular intracellular behavior of hLHß. To investigate the carboxyl terminus polymorphism of natural hLHß, monoclonal antipeptide antibodies were raised against a synthetic peptide mimicking the 104–119 portion of hLHß. One antibody, designated LHP09, was found to specifically react with the recombinant hLHß ending at position hLHß[Leu¹¹⁹] but not with other recombinant forms ending at [Ser¹¹⁶], [Phe¹²⁰] or [Leu¹²¹]. Immunochemical analysis of hLH, either pituitary or urinary in origin, indicated that only pituitary hLH contains a Leu¹¹⁹-ending form of hLHß. Finally, immunohistochemical detection was performed using LHP09 and showed specific staining of a normal adult pituitary gland. These observations support the in vivo existence of intrapituitary molecular forms of hLHß ending at various positions between Gln¹¹⁴ and Leu¹²¹.

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