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J Brtko

Publications and source records attributed to J Brtko.

88 records · Page 5Linked to original sources
PubMed1985

Specific receptors for thyroxine in nuclear non-histone proteins of rat thymus during early, medium and late period of life.

Specific binding of 125I-thyroxine to thymus nuclear non-histone proteins of rats aged 7, 14, 45, 80 and 365 days was studied. In 0.4 mol l-1 NaCl nuclear extract of thymocytes practically the same values of Ka were found in rats aged 7, 14, 45 and 80 days (5.72 +/- 0.11 X 10(9) l mol-1, 3.44 +/- 1.65 X 10(9) l mol-1, 5.00 +/- 1.09 X 10(9) l mol-1 and 5.55 +/- 0.95 X 10(9) l mol-1, respectively). As compared to groups of animals of 7, 45 and 80 days of age a marked diminution of Ka (= 1.30 +/- 0.25 X 10(9) l mol-1) with P less than 0.001, less than 0.02 and less than 0.01, respectively, was found in rats aged 365 days. The highest value representing maximum binding capacity (MBC) of 125I-thyroxine was noted in rats aged 45 days (MBC = 6.16 +/- 0.58 X 10(10) molecules per mg of protein) and in adult rats (80 days old) (MBC = 5.82 +/- 1.28 X 10(10) molecules mg-1). In rats aged 7 days a lower value for MBC (= 1.92 +/- 0.77 X 10(10) molecules mg-1; P less than 0.01) was observed as compared to the animals aged 45 days (see above). Similar decrease was found also in old rats aged 365 days (MBC = 3.46 +/- 0.69 X 10(10) molecules mg-1; P less than 0.02). The data quantify the affinity and the specific 125I-thyroxine binding capacity in nuclear non-histone proteins of rat thymus during early, adult and late period of life.

Aging↗
PubMed1985

Modulation of nuclear receptor affinity for 3,5,3'-triiodothyronine by nucleotide in vitro.

Nuclear non-histone protein fraction containing saturable receptors for thyroid hormone was prepared from rat liver by extraction with 0.3 mol l-1 NaCl. Inhibitory effect of ATP, UTP, GTP and CTP (1 mmol l-1 each) when co-incubated with the nuclear receptor and 3,5,3'-triiodothyronine was demonstrated. The experiments were conducted in the presence of 25 mmol l-1 Na2HPO4 in order to suppress the effect of the phosphate groups of nucleotide molecule by inorganic phosphate. All nucleotides inhibited (P less than 0.05 to 0.001) the specific binding of 3,5,3'-triiodothyronine to soluble receptors in the order ATP greater than CTP greater than GTP greater than UTP. In addition inhibitory effect of 0.5 mmol l-1 ATP on 3,5,3'-triiodothyronine binding to receptors was re-examined by Scatchard plot analysis. The data suggested that the diminution in the specific binding of receptors in the presence of ATP was due to an effect on the equilibrium association constant. The maximum binding capacity of receptors remained unchanged when the concentrations of ATP ranging from 0.1 to 1.0 mmol l-1 were used.

Animals↗
PubMed1984

Specific phosphorylation of nuclear non-histone proteins of rat liver after thyreoidectomy and T4 treatment.

The effect of thyroxine (T4) on phosphorylation of non-histone proteins in rat liver nuclei was studied. Non-histone proteins obtained by extracting liver nuclei with 0.4 mol X l-1 KCl from normal (N), hypothyroid (Tx) and Tx rats treated with T4 (100 micrograms kg-1 B.W.), respectively, were incubated with 32P-ATP at 30 degrees C for 5 min followed by sodium dodecyl sulfate-gradient polyacrylamide gel electrophoresis and autoradiographic analysis. Endogenous phosphorylation in Tx rats was decreased. In T4 treated Tx rats phosphorylation of some proteins was recovered, however the 84 X 10(3) mol wt protein was not completely recovered. Phosphorylation of nuclear nonhistone proteins was not altered by the addition cAMP into the incubation. These findings show that in vitro phosphorylation of non-histone proteins of the rat liver nuclei occurs in some specific fractions which may be thyroid hormone dependent.

Animals↗
PubMed1983

Nuclear receptors for thyroxine in rat liver during postnatal development in relation to DNA-dependent RNA polymerase activity.

Specific binding of 125I-thyroxine on liver nuclear extract of rat fetuses aged 15 and 18 days, of young rats aged 1, 2, 7, 12-14 and 18 days and of adult rats was quantified. The highest value representing the capacity of specific 125I-thyroxine binding was noted in rats aged 7 days. A marked diminution of specific 125I-thyroxine binding was demonstrated in rats aged 12-14 days. Practically the same values of Ka in liver nuclear extract were found in fetuses aged 18 days (Ka = 4.44 X 10(9) 1 mol-1) and in a group of young animals aged 7 days (Ka = 4.17 X 10(9) 1 mol-1). In nuclear extract of the animals aged 12-14 days and in adult rats diminished values (Ka = 2.72 X 10(9) 1 mol-1 and Ka = 1.18 X 10(9) 1 mol-1, respectively) were noted in comparison with the above-mentioned groups of rats. A positive correlation between the binding of 125I-thyroxine and Mn2+-activated DNA-dependent RNA polymerase activity in liver nuclei of rats aged 4 and 14 days and adult rats was found (r = 0.700). These results support the suggestion that thyroxine in the perinatal period of life plays an important role in the induction of mRNA.

Animals↗
PubMed1983

Rat thymus: demonstration of specific thyroxine receptors in nuclear extract.

Nuclear protein fraction from the nuclei of rat thymus was prepared by extraction in 0.4 mol l-1 NaCl and the presence of saturable thyroxine binding sites was demonstrated. Scatchard analysis revealed one class of high affinity binding sites with Ka = 4.15 X 10(9) 1 mol-1, the maximum binding capacity (expressed as number of ligand molecules per mg of protein) of 5.56 +/- 1.37 X 10(10), was found. Amino acid composition (expressed as mumol per mg of protein) of acid hydrolyzates of rat thymus and liver crude "receptors" for thyroid hormones is presented. The results show that the nuclear protein fraction of thymus, responsible for thyroid hormone binding shows some basic characteristics of non-histone proteins and differs in concentration of lysine, histidine, aspartic acid, proline, methionine and slightly in concentration of glycine, isoleucine and phenylalanine from that obtained from the liver. The data suggest that the rat thymus might be considered as a target tissue for thyroxine.

Amino Acids↗
PubMed1981

Effect of thiol blocking agents on the binding of T3 and T4 in rat liver nuclear extract.

Liver nuclei bind thyroid hormones (T3 and T4) with different binding affinities. In out studies it was estimated that the apparent association constant (Ka) in the liver nuclei for T3 was 8.8 X 10(10) l mol-1 and for T4 was 4.1 X 10(9) l mol-1. We have found that the binding sites for T4 are also saturated by an excess of unlabelled T4 and that saturation was dependent on the purification step of liver binding proteins. In liver nuclear extracts with 0.4 mol l-1 KCl the specific binding of T3 and T4 was blocked with a typical -SH blocking agent N-ethylmaleinimide (NEM) and by new types of -SH blocking agents such as p-bromphenylisothiocyanate (p-BPI) and 2,3 dicyano-1,4-dithio-9,10 antrachinone (Delan). NEM and p-BPI increased the non-specific binding of T4 and completely abolished specific binding. All these agents blocked the specific binding of T3. These results demonstrate that T3 and T4 binding sites in the liver nuclei may not be altogether identical and that the different effects of -SH blocking agents on the binding of T3 and T4 is probably associated with the structural configuration of these drugs.

Animals↗
PubMed1981

Specific thyroxine nuclear receptors: DEAE-sephadex chromatography of rat liver nuclear extract.

Specific binding of thyroxine to protein fraction obtained by DEAE-Sephadex chromatography of dialyzed (0.4 mol 1-1 KCl) nuclear extract of purified rat liver nuclei was studied. A procedure for several-fold purification of thyroxine nuclear receptor included isolation of purified rat liver nuclei (by centrifugation through 1.7 mol 1-1 sucrose), extraction, dialysis, Sephadex G-100 and DEAE-Sephadex A-50 chromatography. It was found that a protein peak eluting at 0.05 mol 1-1 NaCl does not show any fraction specifically binding thyroxine. However, specific binding of nuclear receptor for thyroxine was found in a peak eluting at 0.20 mol 1-1 NaCl, the capacity being about 600 fmol mg-1 protein. Moreover, total binding capacity of intact rat liver homogenate, nuclei, non-dialyzed and dialyzed (0.4 mol 1-1 KCl) nuclear extract, Sephadex G-100 and DEAE-Sephadex A-50 chromatography protein fractions for thyroxine was tested. A marked increase (about 20 fold) in the total thyroxine binding expressed in fmol mg-1 of protein in DEAE-Sephadex A-50 eluate was found as compared to whole nuclei, nuclear extract or Sephadex G-100 chromatography fractions. Partial fractionation of rat liver nuclear extract combined with thyroxine binding studies demonstrated that rat liver nuclei contain a non-histone protein fraction--a receptor that is responsible for a specific binding of thyroxine.

Animals↗
PubMed1980

Thyroid hormone binding sites in rat liver nuclear fraction.

The specific binding of 125I-thyroxine and 125I-triiodothyronine in rat liver nuclei and 0.4 mol 1(-1) KCl nuclear extract is presented. The Scatchard plot analysis for triiodothyronine calculated from the competition curve of isolated nuclei gives Ka = 1.3 x 10(9) mol-1 and from that of nuclear extract gives Ka in the range of 10(8)--10(10) 1 mol-1. Crude nuclear extract of rat liver nuclei (0.4 mol 1(-1) KCl, 5 mmol 1(-1) dithiothreitol) after removing of inorganic KCl on G-25 Sephadex was fractionated on G-100 Sephadex. Two different nuclear protein fractions were obtained and the distribution of 125I-thyroxine and 125I-triiodothyronine in these protein components was tested. 125I-thyroxine binds clearly on both protein fractions, whereas 125I-triiodothyronine binding was found only in the major protein component. The fractionation of nuclear extract incubated with labelled thyroid hormones with or without the excess of 0.04 nmol of thyroxine or triiodothyronine demonstrate a specific binding of both thyroid hormones to major protein component and nonspecific binding of thyroxine to a fraction representing the minor protein component.

Animals↗
PubMed1978

Effect of thiocyanate and other univalent anions on the binding of thyroxine to rat liver nuclei and homogenate.

The binding of thyroxine (125I-T4) in rat liver homogenate and isolated nuclei was investigated in vitro. In homogenate, the binding of T4 was modified by thiocyanate ion (SCN-) added to the incubation mixture as potassium thiocyanate. The displacing effect of SCN- increased with increasing concentrations of this compound, the lowest effective dose being that which significantly displaced T4 from liver homogenate (105 pmol per one ml medium). Moreover, SCN- significantly increased the displacing effect of unlabelled T4. In contrast, however, no effect of SCN- was found on the binding of T4 in the isolated liver nuclei. In sonicated nuclei no effect of SCN- on T4 binding was found, but specific binding of T4 under these circumstances was impaired. Finally, in a homogenate a displacing effect of other univalent anions (BF4-, ClO4- and MnO4-) was found resembling that of SCN-. It is suggested that, in the liver homogenate, SCN- displaces T4 from non-specific binding sites. This view is also supported by the fact that in liver nuclei, where specific binding sites prevail, no effect of SCN- was observed.

Animals↗
PubMedDate not supplied

Nuclear all-trans retinoic acid receptors: in vitro effects of selenium.

The present study was undertaken to investigate the effects of selenite (SeIV) and selenate (SeVI) on the all-trans retinoic acid (RA)-nuclear retinoic acid receptor (RAR) complex formation in rat liver. We also present the data on the in vitro effects of SeIV on the RARalpha and the type I iodothyronine 5'-deiodinase gene expression in the GH4C1 rat pituitary tumor cells. SeIV at 1.0 micromol/L was found to reduce (p < 0.05) the RA specific binding to RAR in rat liver. Dithiothreitol (DTT), a protective agent for sulfhydryl groups, was found to be slightly effective in protecting the RAR binding properties when affected by SeIV. SeVI at 0.1 micromol/L reduced (p < 0.05) the RA specific binding to RAR in liver, as well. Seleno-L-methionine (Se-II) when compared to L-methionine did not exert any inhibitory effect on the formation of the RA-RAR complex. SeIV (up to 2.5 micromol/L) has no inhibitory effect on GH4C1 cell proliferation as well as the prolactin secretion. SeIV at 1.0 micromol/L significantly decreases the rate of mRNA synthesis and/or degradation of the alpha form of the RAR and causes the enhancement of the type I iodothyronine 5'-deiodinase gene expression in GH4C1 cells. The results based on in vitro experiments suggest that inorganic selenium may affect the RA specific binding to their cognate receptor molecules, and it may reduce expression of the gene encoding the RARalpha, with the cell vitality and the cell growth remaining unchanged.

Animals↗
PubMedDate not supplied

Effect of selenite and selenate on rat liver nuclear 3,5,3'-triiodothyronine (T3) receptor.

The present study was undertaken to investigate the effects of selenite (SeIV) or selenate (SeVI) on nuclear T3 receptors of rat liver. Selenite at 0.1 microM (p < 0.01) inhibited the T3 specific binding to rat liver nuclear receptors. The specific binding of the T3 receptor was fully restored when even 1.0 microM selenite was separated from the T3 receptor by gel filtration. No inhibitory effect of selenite (up to 100 microM) on the T3 binding to nuclear receptor was found in the presence of 1.0 mM dithiothreitol. The rate of dissociation of the T3-nuclear receptor complex was effectively increased by 0.1 microM selenite. Selenate up to 1 mM as well as sulfite or sulfate up to 0.1 mM did not exert an inhibitory effect on T3 receptors. The results based on the in vitro experiments suggest that the selenium in the form of selenite may reversibly affect the T3 binding on the receptor molecule.

Animals↗
PubMedDate not supplied

5-benzyloxy-2-thiocyanatomethyl-4-pyranone, a novel heterocyclic compound: synthesis, structure determination and effects on neoplastic cell growth.

The present study was undertaken to prepare a novel 4-pyranone compound 5-benzylaxy-2-thiocyanatomethyl-4-pyranone as well as to investigate its effects on neoplastic cell growth. Three cell lines (murine leukemia L1210, human leukemia K562 and rat pituitary GH4C1 cells) were used in our experiments. The cell growth, DNA, RNA, protein synthesis, and cytoplasmatic protein phosphorylation after the treatment of GH4C1 cells with 5-benzyloxy-2-thiocyanatomethyl-4-pyranone were investigated. We found that the above new 4-pyranone derivative at 2.6 microM significantly (p < 0.05) inhibits neoplastic cell growth, and inhibits (p < 0.05) DNA synthesis.

Animals↗
PubMedDate not supplied

Regulation of selected biological processes in neoplastic cell lines by halogen derivatives of 5-hydroxy-2-hydroxymethyl-4-pyranone.

The present study was undertaken to investigate the effects of eight halogen derivatives of 5-hydroxy-2-hydroxymethyl-4-pyranone on a) neoplastic cell growth, b) DNA, RNA, and protein synthesis, c) cytoplasmic phosphorylation, and d) cAMP accumulation in culture medium. Two neoplastic cell lines (the murine leukemia L1210 and the rat pituitary GH4C1) were used in the present study. The inhibitory effects of the halogen derivatives on GH4C1 cell division when compared to L1210 cells were found to be almost equal. Two halogen derivatives (2-chloromethyl-5-hydroxy-4-pyranone and 6-bromo-5-hydroxy-2-hydroxymethyl-4-pyranone) were found to inhibit DNA, RNA and protein synthesis. Moreover, the electrophoretic profile of low molecular mass cytoplasmic proteins was markedly influenced by certain halogen derivatives of 5-hydroxy-hydroxymethyl-4-pyranone in L1210 cells.

Animals↗