CHARACTERIZATION OF HUMAN LUTROPIN CARBOXYL-TERMINUS ISOFORMS

Human lutropin (hLH) exhibits both carbohydrate and peptidic heterogen eities that affect its biological potency and the duration of its acti vity in vivo. Peptidic changes within the hLH beta-subunit are charact erized as intrachain proteolytic nicking and carboxyl terminus heterog eneity. To date, the carboxyl terminus of hLH beta appears to end at e ither position Gln(114) or Gly(117) as determined by sequencing of pur ified subunit. Furthermore, the complementary DNA for hLH beta predict s a protein containing an additional peptidic stretch, which would mak e the beta-subunit 121 residues long. This extension may be responsibl e for the particular intracellular behavior of hLH beta. To investigat e the carboxyl terminus polymorphism of natural hLH beta, monoclonal a ntipeptide antibodies were raised against a synthetic peptide mimickin g the 104-119 portion of hLH beta. One antibody, designated LHP09, was found to specifically react with the recombinant hLH beta ending at p osition hLH beta[Leu(119)] but not with other recombinant forms ending at [Ser(116)], [Phe(120)] or [Leu(121)]. Immunochemical analysis of h LH, either pituitary or urinary in origin, indicated that only pituita ry hLH contains a Leu(119)-ending form of hLH beta. Finally, immunohis tochemical detection was performed using LHP09 and showed specific sta ining of a normal adult pituitary gland. These observations support th e in vivo existence of intrapituitary molecular forms of hLH beta endi ng at various positions between Gln(114) and Leu(121).