LUTEINIZING-HORMONE RECEPTORS ARE ASSOCIATED WITH NONRECEPTOR PLASMA-MEMBRANE PROTEINS ON BOVINE LUTEAL CELL-MEMBRANES

Biophysical studies of the bovine luteinizing hormone (LH) receptor on luteal cell membranes suggest that this receptor may be part of a lar ger molecular weight structure. We have used 5-iodonaphthyl-1-azide (I NA) to identify plasma membrane proteins near LH receptors on plasma m embranes from bovine corpora lutea. Following binding of eosin isothio cyanate-derivatized ovine LH or human chorionic gonadotropin (hCG), fi ve proteins with molecular weights of 71, 57, 55, 49 and 36 kDa were s electively derivatized with [I-125]-INA following 2 h exposure at 22 d egrees C to 514 nm light. However, there was no fluorescence energy tr ansfer between LH receptors occupied by ovine LH or hCG indicating tha t LH receptors were not self-associated in these membrane preparations . Together these results suggest that, following hormone binding, sing le copies of the LH receptor may exist in large molecular weight struc tures that include non-receptor proteins. (C) 1998 Elsevier Science B. V.