A Second, Lower Affinity Growth Hormone-Binding Protein in Human Plasma*

Abstract

In our previous description of the circulating GH-binding protein (GH-BP) we observed, in addition to the main GH-BP complex, a second macromolecular component designated peak I during gel filtration of [125I]GH-plasma mixtures. This component was not further characterized because of its small magnitude, seeming nonsaturability, and suspected artifactual nature. We have now characterized peak I as the complex of a low affinity BP with GH. To gain a better knowledge of the nature of peak I, whole plasma or plasma fractions containing isolated peak I-BP (ammonium sulfate precipitated or prepared by gel filtration of plasma) were incubated with monomeric [125I]GH and varying concentrations of unlabeled GH. The mixtures were then analyzed by Sephadex G-100 chromatography to separate free from protein-bound GH. Peak I-associated radioactivity was saturable at high concentrations of human GH, but not with animal GHs. Saturation/Scatchard analysis yielded an association constant of 10(5) M-1 and a maximum binding capacity of 15 mg/L plasma. Chemically cross-linked complexes of [125I]GH with isolated peak I BP were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, isoelectric focusing, and two-dimensional electrophoresis. These experiments yielded a mol wt of 124 kD and a pI of 7 for the cross-linked complex. This is in contradistinction to the previously reported high affinity GH-BP complex, which when cross-linked has a mol wt of 76 kD and a pI of 5.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma growth hormone and growth hormone-binding protein during development in the marsupial brushtail possum (Trichosurus vulpecula)

“…This peak was not present when 125 I-hGH alone or recombinant human GHBP and 125 I-hGH were run on the column, and was not displaced by excess GH. This large MW product is likely to be either a low affinity GHBP like that described by Baumann and Shaw (1990) or some multimeric form of the high affinity GHBP.…”

“…GHBPs have been identified in a number of species, including the human (Herington et al 1986), rabbit (Spencer et al 1988), mouse (Smith et al 1989), rat (Baumbach et al 1989), cow (Devolder et al 1993) and chicken (Vasilatos-Younken et al 1991). In the human and several other species, at least two forms of GHBP have been shown to exist: a high affinity, low capacity binding protein (Baumann et al 1986, Herington et al 1986) and a low affinity, high capacity binding protein (Baumann & Shaw 1990). The high affinity GHBP is identical to the extracellular domain of the membrane-bound GHR (Leung et al 1987) and is formed by either alternative splicing of the GHR gene (Baumbach et al 1989, Smith et al 1989, Martini et al 1997 or proteolytic cleavage of the extracellular domain of the GHR (Leung et al 1987, Sotiropoulos et al 1993.…”

Identification and Modulation of a Growth Hormone-Binding Protein in Rainbow Trout (Oncorhynchus mykiss) Plasma during Seawater Adaptation

“…High molecular weight GH-BP has also been detected in human serum. These BPs bind hGH with very low affinity (10 6 -10 5 M Ϫ1 ) and high capacity (between 2 and 15 µg/ml) and are thought not to be related to the GH receptor (Baumann and Shaw, 1990;Tar et al, 1990). However, there are high molecular weight complexes in murine serum (Smith and Talamantes, 1987) and also in the culture medium of cells transfected with rabbit GH-BP cDNA (Edery et al, 1993).…”

Influence of the high-affinity growth hormone (GH)-binding protein on plasma profiles of free and bound GH and on the apparent half-life of GH. Modeling analysis and clinical applications.

“…This high-affinity GH-BP corresponds to the extracellular domain of the tissue growth hormone (GH) receptor (5)(6)(7)(8)(9), and contrasts with an incompletely character-ized low-affinity binding protein that is unrelated to the GH receptor (10,11). High-affinity GH-BP concentrations are very low or dysfunctional in Laron-type dwarfism ( 12,13) and decreased in fetal plasma and in certain GH-resistant populations such as pygmies in Africa or the New Guinea highlands ( 10,(14)(15)(16). Studies in heterologous species (e.g., injection of human GH-BP complexed with human GH into the rat) indicate that the presence of a high-affinity binding protein (BP) can prolong the apparent half-life of GH in plasma (17)(18)(19).…”