ROTATIONAL-DYNAMICS OF LUTEINIZING-HORMONE RECEPTORS AND MHC CLASS-I ANTIGENS ON MURINE LEYDIG-CELLS

We have examined the molecular motions of luteinizing hormone (LH) rec eptor and the Major Histocompatibility Complex Class I antigen on muri ne Leydig cells. Using time-resolved phosphorescence anisotropy method s, erythrosin (ErITC)-derivatized ovine luteinizing hormone (oLH) boun d to the LH receptor appears rotationally mobile with rotational corre lation times of 19.6 +/- 1.3 mu s, 13.3 +/- 2.4 mu s, 9.5 +/- 0.7 mu s and 4.7 +/- 0.5 mu s at 4 degrees C, 15 degrees C, 25 degrees C and 3 7 degrees C, respectively. Rotational correlation times for human chor ionic gonadotropin (hCG)-occupied LH receptors were similar to those o f the ErITC-oLH occupied receptor at each temperature. In addition, bo th oLH- and hCG-occupied LH receptors were laterally mobile in fluores cence photobleaching recovery experiments with diffusion coefficients at 29 degrees C of (5.8 +/- 0.9). 10(-10) cm(2) s(-1) and (2.9 +/- 0.4 ). 10(-10) cm(2) s(-1), respectively. We also measured the rotational correlation time of Class I antigen on murine Leydig cells using ErITC -derivatized 34-12-2S, an anti-Class I monoclonal antibody. Because th ere was no decay of the anisotropy function at 4 degrees C, 15 degrees C, 25 degrees C or 37 degrees C in the absence of oLH or following pr eincubation of Leydig cells with 1 nM oLH, it appears that Class I is rotationally immobile on the 1 ms timescale of our experiments. This r esult is consistent with the presence of Class I antigen in large mole cular weight structures acid may be the result of Class I self-aggrega tion. Further, treatment of cells with anti-Class I antibody had no ef fect on either basal or oLH-stimulated testosterone secretion. Thus, i t appears that this anti-Class I antibody is not LH-mimetic on murine Leydig cells.