Role of phospholipids in the accessibility of LH/hCG receptors in porcine corpora lutea.

The role of phospholipids in the interaction of LH/hCG with membrane-bound and water-soluble receptors was studied. Digestion of porcine corpora lutea (CL) membranes with phospholipase-A2 (PL-A2) diminished, in a dose dependent manner, both phospholipid concentration and binding of 125I-hCG to CL membranes. Treatment of the water-soluble LH/hCG receptor occurring in follicular fluid with PL-A2 produced no inhibitory effect on gonadotropin binding in spite of digestion of phospholipids. The decrease of the accessibility of LH/hCG receptors in CL membranes by PL-A2 was associated with a rise of the rigidity of membrane lipids. Dynamic properties of membranes were monitored by electron spin resonance of 5- and 16-doxyl stearic acid probes. These findings suggest that phospholipids play an important role in the accessibility of membrane-bound LH/hCG receptors, but are not involved in a direct interaction of gonadotropin with the binding sites.