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Biomedical subjects

E Frieden

Publications and source records attributed to E Frieden.

At least 55 records · Page 3Linked to original sources
PubMed1975

Metal ion dependence of the binding of triiodothyronine by cytosol proteins of bullfrog tadpole tissues.

The binding of triiodothyronine by Rana catesbeiana tadpole tail fin, tail muscle, kidney, and liver cytosol was studied using dextran-coated charcoal to separate bound and free hormone. A metal ion dependency was suggested by the fact that EDTA decreased the binding of triiodothyronine 80 to 90% in tail fin and tail muscle cytosol. Inhibition of binding in kidney or liver was less, 40 to 50%. This inhibition could be restored by adding an excess of divalent cations with an order of potency of Mn2+ greater than Ca2+ congruent to Co2+ greater than Sr2+ greater than Ba2+ greater than Mg2+. Other chelators, e.g. o-phenanthroline, 8-hydroxyquinoline, and ethylene glycol bis(beta-aminoethylether)-N,N'-tetraacetate also decreased the binding of triiodothyronine, whereas citrate, oxalate, imidazole, and glycine had no effect. The triiodothyronine binding capacity of tail fin cytosol was reduced by EDTA treatment and dialysis against buffer. Ca2+ in the 1 to 10 mM range and Mn2+ at 1 mM could restore the binding to normal levels. Higher Mn2+ increased binding 70% above normal or to Ca2+-restored levels. The triiodothyronine cytosol binding activity was nondialyzable, heat-labile. pH-dependent, pronase-digestible, but unaffected by incubation with trypsin, RNase, and DNase, suggesting that the cytosol binding sites are acidic proteins. Scatchard analysis of triiodothyronine binding by the cytosol of different tissues, revealed Kassoc of 7.1 x 10(6) M(-1), 11.6 x 10(6) M(-1), 3.6 X 10(6) M(-1), and 68.0 x 10(6) M(-1) for tail fin, tail muscle, kidney, and liver cytosol, respectively. The corresponding maximal binding capacities in picomoles per mg of crude cytosol protein in these four tissues were 10.4, 0.86, 1.3, and 0.04, respectively.

Animals↗
PubMed1975

Properties of the red - violet complex of copper and penicillamine and further insight into its formation reaction.

A characteristic red-violet chromophore which forms in the reaction of cupric ion with beta-sulfhydryl- alpha-amino acids has been attributed by several authors to a mixed-valence Cu3L2 structure. We have isolated and examined the analogous chromophore of the chelating drug penicillamine (beta, beta-dimethyl-cysteine), finding instead a polymeric anion with a mixed valence Cu2L2 repeating unit. Direct evidence for a mixed valence polymer cooroborates earlier conclusions of Wilson and Martin (9). Under oxygen-free conditions the anionic complex forms in essentially quantitative yield according to the following reaction: (see article). It has been established that this reaction is halide ion-dependent. The chromophore may be isolated as a sodium salt. This form was found to be stable, and it possessed no measurable activity as an oxidation catalyst. It was also demonstrated through biological experiments with rabbits that a significant amount of the complex- (between 6 percent and 39 percent) is recovered in the urinary tract following intravenous infusions attaining between 1.8 and 10 ppm copper.

Binding Sites↗
PubMed1975

Iron removal from transferrin by a cell-free amphibian system.

1. Transferrin-bound iron was released by a cell-free solution prepared from Rana catesbeiana immature erythrocytes, showing that cellular integrity is not necessarily a requirement for this process as previously thought. 2. The biological molecule(s) involved in the removal of iron from transferrin is relatively small.

Animals↗
PubMed1975

Iron oxidation and transferrin formation by phosvitin.

The catalytic activity of phosvitin in Fe(II) oxidation and the addition of iron to transferrin were studied under various conditions. It was concluded that the Fe(II) oxidized by phosvitin would bind to apotransferrin, although an appreciable fraction of Fe(III) remained bound to phosvitin. Fe(III) also migrated from phosvitin to apotransferrin. This reaction was first-order with respect to Fe(III)-phosvitin concentration with a half-time (t1/2) of 10 min, and a first-order rate constant, k=0.069min-1, in 700 muM-phosphate buffer, pH 7.2, at 30 degrees C. The catalysis of the oxidation of Fe(III) by phosvitin was proportional to O2 concentration, and is quite different from the relative O2 independence of Fe(II) oxidation as catalysed by ferroxidase. A scheme for the mobilization and transfer of iron in the chicken, including the role of ferroxidase, phosyitin and transferrin, is presented.

Animals↗
PubMed1975

Binding by thyroid hormones by nuclei of cells from bullfrog tadpole tail fins.

The regression of the tadpole tail is under the direct control of the thyroid hormones and offers a unique system for the study of the action of these hormones. We have examined the binding of L-triiodothyronine (T3) and L-thyroxine (T4) in vitro using tail fin bricks which included epidermal and connective cells. The binding of 125I-labeled hormones was followed in both nuclear and extranuclear fractions. High affinity and limited capacity sites for T3 and T4 were observed only for the nuclear fraction. Scatchard plots gave similar apparent dissociation constants for both hormones, about 10(-10)M. The maximum number of binding sites per nucleus for T3 was about 1500 and for T4 about 800. There was no significant change in the chemical identity of [125I]T3 and [125I]T4 which was associated with binding in the nuclei. Nuclear binding of [125I]T4 was inhibited competitively for both unlabeled T3 and T4, but unlabeled T3 displaced [125I]T3 significantly more than unlabeled T4. Thus, both binding and competition data support the conclusion that tadpole tail nuclei had more T3 than T4 binding sites.

Animals↗
PubMed1975

Binding of thyroxine and triiodothyronine by nuclei of isolated tadpole liver cells.

The binding of L-triiodothyronine (T3) and L-thyroxine (T4) to cytoplasm and nuclei has been studied in isolated Rana catesbeiana tadpole liver cells. Nuclear binding for both thyroid hormones occurred more slowly at 4 C than at 25 C, but reached the same level as at 25 S. Scatchard analyses suggest high affinity, saturable binding sites for both hormones in the nuclear but not in the cytoplasmic fraction. Apparent equilibrium dissociation constants were 6.8 X 10(-10)M and 4.6 X 10(-10)M for T3 and T4, respectively. The maximum number of binding sites per nucleus for T3 was about 12,300 and for T4 about 2,300. Unlabeled T3 competed for the binding of [125I]T3 to nuclei more effectively than unlabeled T4. No difference in the competition of [125I]T4 binding with non-radioactive T3 or T4 was found. Chromatographic analysis of the bound nuclear radioactivity demonstrated no chemical modification for either hormone.

Animals↗
PubMed1974

The release of iron from horse spleen ferritin by reduced flavins.

Ferritin-Fe(III) was rapidly and quantitatively reduced and liberated as Fe(II) by FMNH(2), FADH(2) and reduced riboflavin. Dithionite also released Fe(II) from ferritin but at less than 1% of the rate with FMNH(2). Cysteine, glutathione and ascorbate gave a similar slower rate and yielded less than 20% of the total iron from ferritin within a few hours. The reduction of ferritin-Fe(III) by the three riboflavin compounds gave complex second-order kinetics with overlapping fast and slow reactions. The fast reaction appeared to be non-specific and may be due to a reduction of Fe(III) of a lower degree of polymerization, equilibrated with ferritin iron. The amount of this Fe(3+) ion initially reduced was small, less than 0.3% of the total iron. Addition of FMN to the ferritin-dithionite system enhanced the reduction; this is due to the reduction of FMN by dithionite to form FMNH(2) which then reduces ferritin-Fe(III). A comparison of the thermodynamic parameters of FMNH(2)-ferritin and dithionite-ferritin complex formation showed that FMNH(2) required a lower activation energy and a negative entropy change, whereas dithionite required 50% more activation energy and showed a positive entropy change in ferritin reduction. The effectiveness of FMNH(2) in ferritin-Fe(III) reduction may be due to a specific binding of the riboflavin moiety to the protein portion of the ferritin molecule.

Animals↗