Water-soluble hepatic growth hormone receptors: structural studies using gel chromatography and chemical...

Gel filtration of a water-solubilized human GH (hGH)-binding protein from rabbit liver has indicated that the binding species as determined by polyethylene glycol precipitation, was of mol wt greater than or equal to 300,000. In contrast, gel filtration of 125I-hGH-binding protein complex revealed in addition a major binding species of mol wt approximately 100,000. This species was shown not to be detectable by polyethylene glycol precipitation. Further, this same binding protein was observed after incubation with 125I-bovine GH but not 125I-ovine PRL, suggesting that it was specific for the somatotrophic but not lactogenic receptor of pregnant rabbit liver. Covalent cross-linking studies using disuccinimidyl suberate and sodium dodecyl sulfate gel electrophoresis, under reducing and nonreducing conditions, revealed a predominant binding subunit of mol wt 57,000, as well as smaller amounts of a mol wt 124,000 species. These data indicate that the structure of the binding protein involves no intersubunit disulfide bonds and suggest that the primary hGH binding subunit of pregnant rabbit liver has a mol wt of 57,000 and exists naturally as a dimer (mol wt, 100-124,000) and perhaps larger oligomers of mol wt greater than or equal to 300,000.