In vitro triiodothyronine binding to non-histone proteins from rat liver nuclei

$\text{In vitro}$ incubations of non-histone proteins from rat liver nuclei with labelled L-3, 5, 3′ triiodothyronine demonstrate the existence of high affinity, limited capacity binding sites for the hormone in this protein group; the affinity was found identical for triiodothyroacetic acid and lower for L-thyroxine. Binding ability was highly temperature dependent. At 4°C, the rate constant of association was 0.9 × 10⁷ M^?1 h^?1 and the rate constant of dissociation was 0.015 h^?1. The dissociation constant K_d was calculated from these data or measured by Scatchard analysis and found to be between 1.6 and 5 × 10^?9 M. The maximum binding capacity was 10^?13 moles of L-3, 5, 3′ triiodothyronine per 100 μg non-histone proteins or 6000 hormone molecules per nucleus. Protein binding had a half-life of 20 hours at 4°C, in the absence of hormone, but was found to be very stable in the presence of hormone.     

Inner compartment localization of heart mitochondrial nucleoside diphosphokinase

Mitochondria isolated from rat heart contained nucleoside diphosphokinase (EC 2.7.4.6) at a specific activity of 30 mIU/mg protein, or about one half of liver mitochondrial activity, 60 mIU/mg. In contrast to liver mitochondria, no stimulation of O₂ uptake was observed when 150 μM GDP was added to heart mitochondria respiring in post-ADP State 4, and the transphosphorylation of [γ-³²Pi] from ATP into GTP was marginal. However, when heart mitochondria pretreated with oligomycin were solubilized with 0.03% Triton X-100, a five fold increase in the rate of GTP formation was observed. These results show that in heart mitochondria approximately 80% of the nucleoside diphosphokinase activity is localized within the inner compartment.     

Effect of thyroid hormone analogues on the displacement of 125I-L-triiodothyronine from hepatic and heart nuclei in vivo: possible relationship to hormonal activity

The capacity of iodotyrosines and iodothyronine analogues to displace tracer[¹²⁵I] L-3,5,3′ triiodothyronine from specific nuclear binding sites in rat liver and heart was related to the displacement capacity of nonradioactive triiodothyronine. Iodotyrosines and L-3,3′,5′ triiodothyronine (“reverse T₃”) were devoid of displacement activity. Analogues with 3,5 substitution in the “inner” ring and single “bulk” substitution in the 3′ position in the phenolic ring exhibited the strongest displacement activity. When the distribution, fractional removal rates and metabolic conversion of the analogues were taken into account, displacement activity appeared to correlate well with the reported thyromimetic activity. These results support the biologic relevance of the nuclear sites.     

Interactions of the chelating agent 2,3-dimercapto-propane-1-sulfonate with red blood cells in vitro. I. Evidence for carrier mediated transport

Uptake of the water soluble 1,2-dimercaptopropanol (BAL) derivative 2,3-dimercapto-1-sulfonate (DMPS) into human red blood cells was found in vitro and the mode of penetration studied in detail. The compound entered erythrocytes in a concentration dependent manner. In contrast to sealed ghosts where inside and outside concentrations reached the same value, DMPS accumulated in intact erythrocytes. Since no binding of DMPS could be detected, the reason for accumulation was assumed to be a conversion of DMPS into chelates or metabolites which penetrated the membrane in a slower rate. A facilitated transport of DMPS mediated by the anion carrier protein was concluded on the basis of the following similarities with the anion transport: inhibition of [¹⁴C]DMPS-uptake by N-ethylmaleimide (NEM), tetrathionate (90%), sulfate (50%), 5,5′-dithio bis(2-nitrobenzoic acid) (DTNB) (25%); inhibition of uptake and efflux by 4,4′-diisothiocyano-2,2′-stilbene disulfonate (DIDS) (80%), dipyridamole (55%); temperature dependency (activation energy 24 K_cal/mol); pH-dependency (pH optimum about 6.9); counter-transport; activation of uptake by preincubation with DMPS (transmembrane effect).     

A peptide derived from the putative transmembrane domain in the tail region of E. coli toxin hemolysin E assembles in phospholipid membrane and exhibits lytic activity to human red blood cells: Plausible implications in the toxic activity of the protein

Hemolysin E (HlyE), a pore-forming protein-toxin and a potential virulence factor of Escherichia coli, exhibits cytotoxic activity to mammalian cells. However, very little is known about how the different individual segments contribute in the toxic activity of the protein. Toward this end, the role of a 33-residue segment comprising the amino acid region 88 to 120, which contains the putative transmembrane domain in the tail region of HlyE has been addressed in the toxic activity of the protein-toxin by characterizing the related wild type and mutant peptides and the whole protein. Along with the 33-residue wild type peptide, H-88, two mutants of the same size were synthesized; in one mutant a conserved valine at 89^th position was replaced by aspartic acid and in the other both glycine and valine at the 88^th and 89^th positions were substituted by aspartic acid residues. These mutations were also incorporated in the whole toxin HlyE. Results showed that only H-88 but not its mutants permeabilized both lipid vesicles and human red blood cells (hRBCs). Interestingly, while H-88 exhibited a moderate lytic activity to human red blood cells, the mutants were not active. Drastic reduction in the depolarization of hRBCs and hemolytic activity of the whole toxin HlyE was also observed as a result of the same double and single amino acid substitution in it. The results indicate an important role of the amino acid segment 88-120, containing the putative transmembrane domain of the tail region of the toxin in the toxic activity of hemolysin E.