Characterization of the growth hormone-binding protein of human serum using a panel of monoclonal antibodies

Abstract

ABSTRACT A panel of monoclonal antibodies (MAbs) reactive with distinct epitopes on the rabbit liver GH receptor and rabbit serum GH-binding protein (GHBP) were tested for cross-reactivity with the GHBP from human serum. Four of seven MAbs reacted with the human serum GHBP. Immunoprecipitation of the human binding protein enabled hormonal specificity identical to that previously reported for human GH receptors to be demonstrated. Scatchard analyses of 125I-labelled human GH binding to the serum GHBP were carried out with correction made for endogenous human GH which was measured by radioimmunoassay of each serum sample. This approach yielded the first reliable estimates of the affinity and capacity of the human GHBP. The binding capacity (mean ± s.e.m.) of female sera (804±126 pmol/l; n= 6) was greater than that of male sera (505 ± 36 pmol/l; n=9; P < 0·02). The affinity of the GHBP was 0·91 ±0·10 litres/nmol (n= 15). The presence of multiple epitopes common to the human serum GHBP and the rabbit liver GH receptor is consistent with identity between the extracellular domains of the human GHBP and the human GH receptor, as is the case for the rabbit GHBP and GH receptor. Journal of Endocrinology (1989) 123, 327–332