(A) Multiple forms of ovarian LH/hCG receptors have been reported by our laboratory and confirmed by others (Mr range 16,000-18,000 under non-denaturing conditions). This contrasts with our previous observations on the LH receptors of Leydig cells, for which a dimeric form was demonstrated. (B) LH receptors were resolved functionally from adenylate cyclase. Rapid membrane events that are initiated after hormone interaction with specific receptors include increased binding of guanyl nucleotide (G) and G-induced phosphorylation, a cAMP independent process. This stimulatory event requires a low Ca++ concentration but is inhibited by high Ca++ concentrations. Similar reduction of basal and hCG-stimulated adenylate cyclase in the presence of G indicated interdependence between these events during membrane activation. (C) Initial studies have indicated the existence of masked ovarian particulate receptors. Crosslinking studies have demonstrated that the prolactin receptor is a protein of Mr 80,000 containing a 40,000 Mr subunit. The above studies were extended as follows: (A) Studies on labeling affinity purified ovarian LH receptors have yielded receptor with low bindability to a subsequent affinity column step. The eluted tracer gave a single form of Mr 60,000 on SDS analysis. (B) During guanyl nucleotide-induced phosphorylation, not only an increase but also an apparent shift from phosphothreonine to phosphoserine takes place. G nucleotides affect membrane phosphorylation in the same potency order with which they bind to membranes. (C) The ovarian prolactin receptor has been purified to near-homogeneity in low yield, and contains Mr 40,000 and 80,000 protein bands after SDS analysis and silver staining. We will proceed with the characterization of gonadotropin and prolactin receptors of the testis and ovary, and with studies on the physical and functional relationships of the LH receptor site and the individual adenylate cyclase components.