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Structural and functional microheterogeneity of rat thyroxine-binding globulin during ontogenesis
M Rouaze-Romet1, R Vranckx, L Savu
1INSERM U224, affiliée au CNRS, Faculté de Médecine Xavier Bichat, Paris, France.
The Biochemical Journal
|August 15, 1992
Summary
Rat thyroxine-binding globulin (TBG) isoforms change binding affinity during development. Liposoluble serum components inhibit binding in neonates, affecting thyroid hormone transport. Further research is needed to clarify physiological significance.
Area of Science:
- Biochemistry
- Developmental Biology
- Endocrinology
Background:
- Thyroxine-binding globulin (TBG) is the primary carrier of thyroid hormones.
- In rats, TBG levels surge post-natally and decline in adults.
- TBG exhibits microheterogeneity with age-dependent changes.
Purpose of the Study:
- To investigate the structural and binding characteristics of rat TBG isoforms during development.
- To analyze age-related changes in TBG isoform abundance and T4 binding.
- To explore the influence of serum components on TBG binding properties.
Main Methods:
- Isoelectric focusing (IEF) to analyze TBG isoforms and their sialic acid content.
- 125I-thyroxine (T4) labeling to assess binding affinities.
- Crossed immunoelectrofocusing to determine isoform proportions.
- Analysis of serum lipidic extracts and their effect on TBG binding.
Main Results:
- Six labeled TBG isoforms (pI 4.25-4.55) were identified, differing in sialic acid content.
- T4 binding shifted from less sialylated (neonates) to more sialylated isoforms (adults).
- Isoform proportions remained constant, with acidic forms predominating.
- Liposoluble serum components inhibited binding in neonatal TBG isoforms.
Conclusions:
- Rat TBG isoform proportions are stable during development.
- Neonatal serum composition, particularly lipid-soluble factors, impairs binding of abundant TBG isoforms.
- Serum environment significantly influences TBG isoform binding properties during ontogeny.