SOLUBILIZATION AND CHARACTERIZATION OF A GROWTH-HORMONE SECRETAGOGUE RECEPTOR FROM PORCINE ANTERIOR-PITUITARY MEMBRANES

The discovery of a potential new GH therapy by small molecules that in duce GK secretion (GHRP-6, L-692,429, MK-0677), has increased the inte rest in these GH secretagogues and their receptor and mechanism of act ion, which is different from the one of GHRH. We report the solubiliza tion of the GH-secretagogue-receptor-ligand-G-protein complex (apparen t molecular mass of approximately 255 kDa) from porcine anterior pitui tary membranes using dipitonin, after labelling the receptor with [S-3 5]MK-0677. The solubilized receptor showed high affinity (K-D = 122.2 +/- 14.4 pM) and low capacity (B-max = 3.8 +/- 0.9 fmol/mg protein). T hese values and the inhibition constants (K-1) for a series of GH secr etagogues were similar to the values determined in membranes isolated from porcine anterior pituitary gland. The solubilization of the GH se cretagogue receptor opens up the possibility for further molecular cha racterization and sequencing of the receptor protein, necessary step p rior to the identification of the natural ligand that would act as a G HRH amplifying hormone, and that the GH secretagogues would mimic. (C) 1996 Academic Press, Inc.