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Characterization of human thyroxine-binding globulin. Evidence for a single polypeptide chain
The Journal of Biological Chemistry
|December 10, 1977
Summary
Thyroxine-binding globulin (TBG) is a single polypeptide chain, not composed of subunits. This finding clarifies the structure of this important thyroid hormone transport protein.
Area of Science:
- Biochemistry
- Proteomics
- Endocrinology
Background:
- Thyroxine-binding globulin (TBG) is crucial for transporting thyroid hormones in the blood.
- Understanding TBG's molecular structure is essential for comprehending its function and interactions.
Purpose of the Study:
- To purify and characterize thyroxine-binding globulin (TBG) from human plasma.
- To determine the subunit composition and molecular properties of TBG.
Main Methods:
- Purification using affinity, anion exchange, and gel filtration chromatography.
- Analytical ultracentrifugation, electrophoresis, and spectroscopic analysis.
- Chemical and physical methods to assess subunit structure (e.g., COOH-terminal analysis, peptide mapping, SDS treatment).
Main Results:
- Purified TBG exhibited a single band on electrophoresis, indicating homogeneity.
- Determined molecular weight of 54,000 and carbohydrate content of 23%.
- Multiple lines of evidence consistently failed to detect subunits, supporting a single polypeptide chain structure.
Conclusions:
- Thyroxine-binding globulin (TBG) exists as a single polypeptide chain.
- This structural elucidation provides a foundation for further studies on TBG's role in thyroid hormone transport and regulation.