Chemical differences between thyrotropin isohormones

Differential expression and regulation of thyrotropin (TSH) in T cell lines

The immune system's production of and response to thyrotropin (TSH) suggests the existence of a hypothalamic-lymphoid-thyroid regulatory axis (HLT). To evaluate the possible roles of lymphocyte-derived TSH we characterized its structure and regulation of production. Using an in vitro system, we screened T cell lines for the production of TSH in response to thyrotropin-releasing hormone (TRH). We identified MOLT 4 T cells as producers of intact TSH based on TSH radioimmunoassay (RIA) displacement and de novo synthesized protein structure similar to pituitary TSH. Northern blot analysis using a cDNA probe to TSH beta showed the existence of an mRNA species similar in molecular size to pituitary mRNA of TSH beta. The MOLT 4-derived TSH is induced in a dose-dependent fashion by TRH and that induction is significantly inhibited by the thyroid hormone, triiodothyronine (T3). HUT 78 T cells express an mRNA species similar to TSH beta but do not express detectable protein suggesting a lack of translation of the mRNA species. The evidence suggests that the MOLT 4 T cells serve as an in vitro model for TSH production and may be used to study differential expression of the genes for TSH in the immune system. Elucidation of this in vitro system will provide information on mechanisms of regulation of an HLT axis that are unique to the immune system as well as pathways common to the immune and neuroendocrine systems.

High-performance liquid chromatography of amino acids, peptides and proteins. LXXV. Isolation of isohormones of bovine thyrotropin and lutropin

Purification of bovine thyrotropin and lutropin by conventional soft-gel chromatographic methods is shown to yield microheterogeneous products. High-performance ion-exchange chromatography (HPIEC) can be used to purify these isohormones further for investigations into the structure/function role of glycoprotein microheterogeneity. Hormonal microheterogeneity is shown to be reflected in differences in surface-accessible charged groups, as demonstrated by HPIEC, and differences in net charge, as indicated by isoelectric focusing. Optimal separation of the glycoprotein hormones, based on protein charge, can therefore be achieved by a combination of these two methods.

Pituitary thyrotropin and gonadotropin of coho salmon (Oncorhynchus kisutch): separation by chromatofocusing

Thyrotropin (TSH) and gonadotropin (GTH) were isolated from adult female coho salmon pituitary glands. After final extraction in acidic alcohol and precipitation in 85% ethanol, proteins were fractionated using gel filtration chromatography and chromatofocusing. Homologous bioassay systems were used to monitor bioactivity during the purification procedures. TSH activity was measured in vivo in coho salmon parr. GTH (steroidogenic) activity was determined in vitro using cultures of adult coho salmon ovarian follicles. Using these procedures, TSH and GTH activities were separated. TSH activity eluted as one major peak at pH 6.3 whereas GTH activity eluted as five major peaks at pH's 5.4, 5.0, 4.7, 4.3, and after 1.0 M NaCl on chromatofocusing. Molecular weights of the TSH and GTHs were estimated by gel filtration chromatography as 35 and 40 kDa, respectively. Like other vertebrate TSHs and gonadotropins, the coho salmon TSH and GTHs appeared to consist of two subunits. Coho salmon TSH and bovine TSH (bTSH) were equipotent in the TSH bioassay. The five coho salmon GTHs exhibited similar potencies in stimulating ovarian estradiol synthesis in vitro. Further biochemical analysis and tests for other gonadotropic activities are warranted to determine if these five GTHs are isoforms of one GTH or if they can be distinguished functionally in other GTH bioassays. Sufficient quantities of coho salmon TSH were isolated in this study for future studies of the hypothalamic-pituitary-thyroid axis in fish.

Pituitary gonadotropic hormone from a chondrostean fish, starred sturgeon (Acipenser stellatus Pall.) III. Polymorphism

Four biologically active fractions of gonadotropic hormone (aci-GTH-A, -B, -C, -D) were isolated and purified from acetonized pituitaries of the starred sturgeon (Acipenser stellatus Pall.). Their separation was achieved by DEAE-cellulose chromatography. Disc-electrophoresis and especially isoelectric focusing in polyacrylamide gel showed that each fraction contained several components. Not less than 15 different components as a whole with isoelectric points ranging from 4.5 to 7.0 could be counted in four aci-GTH preparations. All these components were active in toad oocyte maturation test. Only two of four preparations (aci-GTH-A and -D) were practically free of common components. All aci-GTH preparations were shown to be homogeneous and identical by molecular weight, sedimentation coefficient, sialic acid content, and some immunological properties. N-terminal amino acid analysis revealed tyrosine and leucine in all aci-GTH preparations, with the only exception of aci-GTH-D that contained an additional polypeptide with N-terminal glycine. No differences in the spectra of aci-GTH isoforms were found when pituitary extract, newly purified or 3 years older hormone preparations were submitted to isoelectric focusing.

Charge-state and charge-continuum models in electrophoresis and isoelectric focusing of genetic variants

A model which combines the charge-state and charge-continuum models is considered in terms of the pH at which the electrophoretic analysis is made. "Unit" charge changes are obtained when the mutated charged group is at least 2 pH units apart from the pI of the protein. "Fractional" charge changes are found when the differences between the pK of the mutated charged group and the pI of the protein becomes progressively smaller, or when the pK of the ionizable group lies on the "wrong" side of the protein pI. It is possible to measure the pK of a modified group in a protein when the delta pI per protonic unit in a given family of proteins (e.g., haemoglobin mutants) is less than unity.