Purification, molecular cloning, and functional expression of the human nicodinamide-adenine dinucleotide phosphate-regulated thyroid hormone-binding protein.

The kidney and several other thyroid hormone-responsive tissues contain a NADP-regulated thyroid hormone (TH)-binding protein (THBP), with an apparent molecular mass of 36 kDa on SDS-PAGE, responsible for most of the intracellular high-affinity T3 and T4 binding. THBP was purified to homogeneity from human kidney cytosol and used to generate proteolytic peptides. Microsequencing of four peptides revealed identity to amino acid sequences deduced from a human cDNA homolog to a cDNA encoding kangaroo mu-crystallin.

Solubilization, reconstitution and molecular properties of the triiodothyronine transport protein from rat erythrocyte membranes.

Triiodothyronine (T3) transport through the mammalian erythrocyte membrane is mediated by a transport system related to the aromatic amino acid transport system T. The T3-binding component of this transport system could be photolabeled with [125I]T3 as a 52-kD protein, and subsequently solubilized with non-ionic detergents. Upon purification by ion-exchange chromatography, the photolabeled 52-kD protein solubilized with octylglucoside (OG) resolved into several peaks, suggesting charge heterogeneity of labeled proteins.

Identification by photoaffinity labeling of a membrane thyroid hormone-binding protein associated with the triiodothyronine transport system in rat erythrocytes.

Photoaffinity labeling with underivatized T3 was used to identify T3-binding proteins in the membrane of rat erythrocytes. UV irradiation of ghosts and peripheral protein-depleted membranes in the presence of [125I]T3 resulted in the covalent attachment of 125I to membrane proteins (analyzed by polyacrylamide gel electrophoresis and autoradiography). In the presence of the free radical scavenger dithiothreitol, 125I was selectively incorporated into a 45,000 mol wt band (p45) that was an integral membrane polypeptide.

Triiodothyronine binding sites in the rat erythrocyte membrane: involvement in triiodothyronine transport and relation to the tryptophan transport System T.

The binding of L-triiodothyronine (T3) to rat erythrocyte membranes (ghosts and peripheral protein-depleted vesicles) was studied under equilibrium conditions. Ghosts contained high-affinity T3 binding sites whose dissociation constant (21 nM) was similar to the equilibrium-exchange Michaelis constant of T3 transport measured in ghosts. Each ghost contained about 8.

Transport of thyroid hormones by human erythrocytes: kinetic characterization in adults and newborns.

The uptake of [125I]T3 and [125I]T4 by human erythrocytes was studied. The erythrocytes were obtained from adult subjects (28-41 yr old) and suspended in a protein-free medium. The half-times of equilibration for both T3 and T4 were 6 min.