ROTATIONAL-DYNAMICS OF LUTEINIZING-HORMONE RECEPTORS ON BOVINE AND OVINE LUTEAL CELL PLASMA-MEMBRANES

To determine whether LH receptor rotational diffusion is similar in cl osely related species, we compared the rotational correlation times of LH receptors on bovine CL membranes with those of LH receptors on she ep small luteal cells and luteal cell plasma membranes using time-reso lved phosphorescence anisotropy techniques. After binding of erythrosi n isothiocyanate (ErlTC)-derived bovine LH (bLH), ErlTC-ovine LH (oLH) , or ErlTC-hCG, there was no difference in the initial and final aniso tropy at 4 degrees C, 15 degrees C, 25 degrees C, and 37 degrees C, in dicating that the bLH receptor was rotationally immobile on the time s cale of our experiments. On these same membrane preparations, the epid ermal growth factor (EG Fl receptor occupied by ErlTC-murine EGF exhib ited temperature-dependent rotational correlation times of 80 +/- 5 mu sec, 111 +/- 7 mu sec, 254 +/- 4 mu sec, and > 1000 mu sec at 4 degre es C, 15 degrees C, 25 degrees C, and 37 degrees C, respectively. Slow er rotational times for EGF receptor observed at higher temperatures s uggested the occurrence of temperature-dependent receptor aggregation. Like the bLH receptor, the oLH receptor on intact cells and on CL pla sma membranes was rotationally immobile on the time scale of our exper iments when occupied by ErlTC-hCG. However, the oLH-occupied receptors on small luteal cells and on luteal cell membranes had comparable rot ational correlation times at 37 degrees C. These results suggest that bLH receptors are present in large, rotationally immobile structures, whereas the receptor-containing structure formed on ovine luteal cells depends on whether that receptor is occupied by hCG or oLH. Also, des pite the similarities between reproductive function in these species, the LH-occupied receptor appears to be organized differently in the pl asma membranes of these hormone-responsive luteal cells.