Transthyretin: Thyroid and Vitamin A Carrier Protein

The thyroid hormones associate with three types of simple proteins in the serum: Transthyretin (prealbumin), thyroid binding globulin, and albumin. -Ray Peat, PhD

Transthyretin, which carries both vitamin A and thyroid hormones, is sharply decreased by stress, and should probably be regularly measured as part of the thyroid examination. -Ray Peat, PhD

Clin Chem Lab Med. 2002 Dec;40(12):1344-8.
Transthyretin: its response to malnutrition and stress injury. clinical usefulness and economic implications.
Bernstein LH, Ingenbleek Y.
Serum transthyretin is an ideal marker for monitoring patients who are malnourished or have metabolic consequences of acute stress injury because it has a short half-life, it measures the level of metabolic deficit, the response to nutritional metabolic support, and because it is a prognostic indicator. Mounting clinical evidence indicates that the use of transthyretin to assess and monitor a patient’s nutritional status results in improved treatment outcomes and lower overall healthcare costs.

Transthyretin, carrying the thyroid hormone, enters the cell’s mitochondria and nucleus (Azimova, et al., 1984, 1985). In the nucleus, it immediately causes generalized changes in the structure of chromosomes, as if preparing the cell for major adaptive changes. Respiratory activation is immediate in the mitochondria, but as respiration is stimulated, everything in the cell responds, including the genes that support respiratory metabolism. –Ray Peat, PhD

Biokhimiia. 1984 Sep;49(9):1478-85.
[The nature of thyroid hormone receptors. Thyroxine- and triiodothyronine-binding proteins of mitochondria].
[Article in Russian]
Azimova ShS, Umarova GD, Petrova OS, Tukhtaev KR, Abdukarimov A.
T4- and T3-binding proteins of rat liver were studied. It was found that the external mitochondrial membranes and matrix contain a protein whose electrophoretic mobility is similar to that of thyroxine-binding blood serum prealbumin (TBPA) and which binds either T4 or T3. This protein is precipitated by monospecific antibodies against TBPA. The internal mitochondrial membrane has two proteins able to bind thyroid hormones, one of which is localized in the cathode part of the gel and binds only T3, while the second one capable of binding T4 rather than T3 and possessing the electrophoretic mobility similar to that of TBPA. Radioimmunoprecipitation with monospecific antibodies against TBPA revealed that this protein also the antigenic determinants common with those of TBPA. The in vivo translocation of 125I-TBPA into submitochondrial fractions was studied. The analysis of densitograms of submitochondrial protein fraction showed that both TBPA and hormones are localized in the same protein fractions. Electron microscopic autoradiography demonstrated that 125I-TBPA enters the cytoplasm through the external membrane and is localized on the internal mitochondrial membrane and matrix.

Biokhimiia. 1984 Aug;49(8):1350-6.
[The nature of thyroid hormone receptors. Translocation of thyroid hormones through plasma membranes].
[Article in Russian]
Azimova ShS, Umarova GD, Petrova OS, Tukhtaev KR, Abdukarimov A.
The in vivo translocation of thyroxine-binding blood serum prealbumin (TBPA) was studied. It was found that the TBPA-hormone complex penetrates-through the plasma membrane into the cytoplasm of target cells. Electron microscopic autoradiography revealed that blood serum TBPA is localized in ribosomes of target cells as well as in mitochondria, lipid droplets and Golgi complex. Negligible amounts of the translocated TBPA is localized in lysosomes of the cells insensitive to thyroid hormones (spleen macrophages). Study of T4- and T3-binding proteins from rat liver cytoplasm demonstrated that one of them has the antigenic determinants common with those of TBPA. It was shown autoimmunoradiographically that the structure of TBPA is not altered during its translocation.

Biokhimiia. 1985 Jan;50(1):114-121.
[The nature of thyroid hormone receptors. The role of serum thyroxine binding prealbumin in the realization of the hormonal effect].
[Article in Russian]
Azimova ShS, Petrova OS, Abdukarimov A.
Data from determination of molecular weight and competitive displacement suggest that T3 and T4 are bound to the same protein in chromatin. It was shown that the antigenic determinants of T3 and T4 for the chromatin-binding protein coincide with those for blood serum thyroxine-binding prealbumin (TBPA). It was found also that the binding either to T3 and T4 decreases proportionally to the amount of the TBPA removed from the subcellular fractions. It may thus be concluded that blood serum TBPA is responsible for the binding to T3 and T4 as well as for the realization of the hormonal response.

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