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Transformed α2‐macroglobulin as a low‐affinity growth hormone‐binding protein
Author(s) -
Kratzsch J,
Selisko T,
Birkenmeier G
Publication year - 1996
Publication title -
acta pædiatrica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.772
H-Index - 115
eISSN - 1651-2227
pISSN - 0803-5253
DOI - 10.1111/j.1651-2227.1996.tb14315.x
Subject(s) - macroglobulin , immunoprecipitation , dissociation constant , proteinase inhibitor , binding protein , binding site , affinity chromatography , biochemistry , plasma protein binding , covalent bond , microbiology and biotechnology , chemistry , biology , receptor , enzyme , gene , organic chemistry
Human growth hormone (GH) forms complexes with the purified proteinase inhibitor, α2‐macroglobulin (α2‐M). This inhibitor occurs in two different forms in serum, known as native and transformed α2‐M. It has been clearly demonstrated, using chromatography and electrophoresis combined with autoradiography, that human GH binds specifically to the transformed inhibitor and not to the native protein. The binding was characterized as being mainly non‐covalent and involved specific binding sites present only in the transformed inhibitor molecule. Binding analysis, using an immunoprecipitation technique, revealed that GH possesses two different types of binding sites, with dissociation constants of 0.49 ± 0.12 μmol/1 and 61 ± 8 μmol/1 for the high‐ and low‐affinity binding site, respectively. Distribution analysis of 125 I‐labelled GH in whole plasma suggests that the hormone is bound to two different proteins: first, to the high‐affinity GH‐binding protein (GHBP) and, second, to the low‐affinity GHBP, identified as transformed α2‐macroglobulin.