IDENTIFICATION AND CHARACTERIZATION OF GROWTH-HORMONE RECEPTORS IN SNAKEHEAD FISH (OPHIOCEPHALUS-ARGUS CANTOR) LIVER

The specific binding of I-125-labeled fish growth hormone (GH) to hepa tic membranes prepared from several freshwater fish was assessed. A hi gh level of growth hormone receptor (GHR) was detected on the hepatic membranes of the snakehead fish (Ophiocephalus argus Canter). Scatchar d analysis of the binding data showed a single class of high affinity binding site with a binding affinity (K-a) of 1.45 +/- 0.23 x 10(9) M- 1 and a binding capacity (B-max) of 198 +/- 57 fmol/mg protein. The bi nding was specific for fish GH and was saturable. In addition, the spe cific binding was temperature-and time-dependent, reaching a steady st ate after 16 hr of incubation at 25 degrees. The molecular weight of G HR as measured by Sephadex G-200 column chromatography and Western blo t analysis using a monoclonal antibody (Mab263) against GHR was found to be 200-400 and 90-93 kDa, respectively. Two bands at 65 and 89 kDa were identified in ligand crosslinking studies of membrane receptors. A sensitive teleost GH radioreceptor assay (RRA) was developed, using recombinant fish GH and a membrane preparation from snakehead fish liv er, capable of measuring bioactive GH in fish sera or other samples. ( C) 1997 Academic Press.