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Transformed alpha 2-macroglobulin as a low-affinity growth hormone-binding protein
J Kratzsch1, T Selisko, G Birkenmeier
1Institute of Clinical Chemistry, University of Leipzig, Germany.
Acta Paediatrica (Oslo, Norway : 1992). Supplement
|October 1, 1996
Summary
Human growth hormone (GH) specifically binds to transformed alpha 2-macroglobulin (alpha 2-M), a proteinase inhibitor found in serum. This interaction involves distinct binding sites, revealing new insights into hormone-protein interactions.
Area of Science:
- Biochemistry
- Endocrinology
- Protein Chemistry
Background:
- Human growth hormone (GH) plays a crucial role in human physiology.
- Alpha 2-macroglobulin (alpha 2-M) is a major proteinase inhibitor present in serum, existing in native and transformed forms.
Purpose of the Study:
- To investigate the specific binding interactions between human GH and alpha 2-M.
- To characterize the binding sites and affinity of GH for alpha 2-M.
Main Methods:
- Chromatography and electrophoresis combined with autoradiography were used to demonstrate GH binding to alpha 2-M.
- Immunoprecipitation techniques were employed to analyze GH binding sites and affinities.
- Distribution analysis of 125I-labelled GH in plasma was performed.
Main Results:
- Human GH specifically binds to the transformed form of alpha 2-M, not the native form.
- The binding is predominantly non-covalent, involving specific sites on transformed alpha 2-M.
- GH exhibits two types of binding sites for alpha 2-M: a high-affinity site (Kd = 0.49 +/- 0.12 mumol/l) and a low-affinity site (Kd = 61 +/- 8 mumol/l).
- Plasma analysis indicated GH binds to both a high-affinity GH-binding protein (GHBP) and a low-affinity GHBP, identified as transformed alpha 2-M.
Conclusions:
- Transformed alpha 2-macroglobulin acts as a low-affinity binding protein for human growth hormone.
- The study identifies distinct binding characteristics and affinities of GH to serum proteins, including transformed alpha 2-M.