Reaction paths of iron oxidation and hydrolysis in horse spleen and recombinant human ferritins

UV-visible spectroscopy, electrode oximetry, and pH stat were used to study Fe(II) oxidation and hydrolysis in horse spleen ferritin (HoSF) and recombinant human H-chain and L-chain ferritins (HuHF and HuLF). Appropriate test reactions and electrode responses were measured, establishing the reliability of oxygen electrode/pH stat for kinetics studies of iron uptake by ferritin. Stoichiometric ratios, Fe(II)/O2 and H+/Fe(II), and rates of oxygen uptake and proton production were simultaneously measured as a function of iron loading of the protein. The data show a clear distinction between the diiron ferroxidase site and mineral surface catalyzed oxidation of Fe(II). The oxidation/hydrolysis reaction attributed to the ferroxidase site has been determined for the first time and is given by 2Fe2+ + O2 + 3H2O --> [Fe2O(OH)2]2+ + H2O2 + 2H+ where [Fe2O(OH)2]2+ represents the hydrolyzed dinuclear iron(III) center postulated to be a mu-oxo-bridged species from UV spectrometric titration data and absorption band maxima. The transfer of iron from the ferroxidase site to the mineral core has been now established to be [Fe2O(OH)2]2+ + H2O --> 2FeOOH(core) + 2H+. Regeneration of protein ferroxidase activity with time is observed for both HoSF and HuHF, consistent with their having enzymatic properties, and is facilitated by higher pH (7.0) and temperature (37 degreesC) and by the presence of L-subunit and is complete within 10 min. In accord with previous studies, the mineral surface reaction is given by 4Fe2+ + O2 + 6H2O --> 4FeOOH(core) + 8H+. As the protein progressively acquires iron, oxidation/hydrolysis increasingly shifts from a ferroxidase site to a mineral surface based mechanism, decreasing the production of H2O2.     

Relationship between sinter properties and iron ore granulation index

Abstract

A range of iron ores were used in varying proportions to prepare 28 different ore mixtures. Each mixture was classified according to its granulation index and sintered in a pilot plant. The resulting sinters were characterised by chemical analysis, degradation during reduction in the blast furnace (reduction degradation index test), cold strength (tumbler test), coke consumption and process productivity. Sinter quality was assessed in relation to the granulation index of the ore mixture.     

Sex difference in distribution and iron responsiveness of the two ferritins of rat cardiac and skeletal muscle

The presence of two electrophoretically and structurally distinguishable forms of ferritin ("fast" and "slow") in cardiac and skeletal muscle (diaphragm) of the rat was confirmed. Although the total amount of cardiac ferritin showed no difference in concentration in male and female rats, the distribution between the fast and slow species was markedly different in the two sexes, the fast form predominating in the cardiac muscle and diaphragm of the female. In agreement with this, the rates of synthesis and of degradation of the fast species were greater in the female, while the opposite obtained for the male. Iron administration stimulated synthesis of each ferritin species in the cardiac muscle and diaphragm of both sexes. Induction of cardiac connective tissue hypertrophy with isoproterenol inverted the ratio of slow to fast ferritin in female rats, while iron administration along with isoproterenol restored this to normal. It is concluded that the metabolism of ferritin in cardiac and skeletal muscle is sensitive both to sexual status and to iron administration.     

Relationship between esophageal atresia with tracheoesophageal fistula and vertebral anomalies in mammalian embryos

During the last years it became obvious that a lot of families of long-range repetitive DNA elements are located within the genomes of mammals. The principles underlying the evolution of such families, therefore, may have a greater impact than anticipated on the evolution of the mammalian genome as a whole. One of these families, called chAB4, is represented with about 50 copies within the human and the chimpanzee genomes and with only a few copies in the genomes of gorilla, orang-utan, and gibbon. Members of chAB4 are located on 10 different human chromosomes. FISH of chAB4-specific probes to chromosome preparations of the great apes showed that chAB4 is located, with only one exception, at orthologous places in the human and the chimpanzee genome. About half the copies in the human genome belong to two species-specific subfamilies that evolved after the divergence of the human and the chimpanzee lineages. The analysis of chAB4-specific PCR-products derived from DNA of rodent/human cell hybrids showed that members of the two human-specific subfamilies can be found on 9 of the 10 chAB4-carrying chromosomes. Taken together, these results demonstrate that the members of DNA sequence families can evolve as a unit despite their location at multiple sites on different chromosomes. The concerted evolution of the family members is a result of frequent exchanges of DNA sequences between copies located on different chromosomes. Interchromosomal exchanges apparently take place without greater alterations in chromosome structure.     

Relationship between the electromagnetic and physicochemical properties of carbonyl iron powder

Summary The relationship is examined between the electromagnetic properties of carbonyl iron powder and some factors involved in the manufacture of this powder. The electromagnetic properties depend on the onion skin structure of the powder particles and the chemical composition and particle size of the powder.Translated from Poroshkovaya Metallurgiya, No. 7 (43), pp. 38–44, July, 1966.     

Relationship between dopamine agonist stimulation of inositol phosphate formation and cytidine diphosphate-diacylglycerol accumulation in brain slices

Dopamine receptor-coupled stimulation of inositol phosphate formation has been characterized extensively, but little is known about the diacylglycerol arm of this dual-signaling pathway. This study examined several parameters of cytidine diphosphate-diacylglycerol (CDP-DG) accumulation as an index of agonist-stimulated DG formation. Rat brain slices pre-labeled with 5-[3H]cytidine were incubated with various test agents in the presence of LiCl and accumulated CDP-DG analyzed. Dopamine and SKF38393 significantly and dose-dependently stimulated CDP-DG accumulation. SKF38393 responses were inhibited by neomycin and reversed by myo-inositol or by exclusion of LiCl. Compared to inositol phosphate formation in 2-[3H]inositol-prelabeled slices, the CDP-DG responses were proportionately greater, while the agonist EC50 values were similar between the two assays. The D1-receptor antagonist SCH23390 inhibited SKF38393-mediated responses at 0.1-10 microM concentrations, whereas greater concentrations reversed the inhibition. SKF38393 effects were completely blocked by the DG kinase inhibitor R59022, thus precluding any role for phospholipase-D or de novo phosphatidate synthesis in the dopaminergic response. D609 which inhibits phosphatidylcholine-specific phospholipase-C (PLC), potently inhibited both CDP-DG accumulation and inositol phosphate formation. These findings demonstrate that the selective D1-receptor antagonist SCH23390 is a partial agonist at the D1-like dopamine receptor that couples to phosphoinositide signaling, that dopaminergic facilitation of phosphoinositide signaling is independent of de novo phosphatidate synthesis, and that the widely used enzyme inhibitor, D-609, is probably not selective for phosphatidylcholine-specific PLC in brain slice preparations. The greater sensitivity of the CDP-DG measurement presents this assay as a reliable and possibly superior index of dopamine receptor-coupled PLC activation in intact tissues.     

Heme oxygenase 1 is required for mammalian iron reutilization

Stressed mammalian cells up-regulate heme oxygenase 1 (Hmox1; EC 1.14.99.3), which catabolizes heme to biliverdin, carbon monoxide, and free iron. To assess the potential role of Hmox1 in cellular antioxidant defense, we analyzed the responses of cells from mice lacking functional Hmox1 to oxidative challenges. Cultured Hmox1(-/-) embryonic fibroblasts demonstrated high oxygen free radical production when exposed to hemin, hydrogen peroxide, paraquat, or cadmium chloride, and they were hypersensitive to cytotoxicity caused by hemin and hydrogen peroxide. Furthermore, young adult Hmox1(-/-) mice were vulnerable to mortality and hepatic necrosis when challenged with endotoxin. Our in vitro and in vivo results provide genetic evidence that up-regulation of Hmox1 serves as an adaptive mechanism to protect cells from oxidative damage during stress.     

Induction of oxidative DNA damage by ferric iron in mammalian cells

Ferric nitrilotriacetate (Fe-NTA) and ferric citrate (Fe-citrate) were compared with respect to their potential to induce oxidative DNA damage in V79 Chinese hamster cells. DNA base modifications, including 8-hydroxyguanine (7,8-dihydro-8-oxoguanine), were quantified by the frequency of lesions recognized by the bacterial Fpg protein (formamidopyrimidine-DNA glycosylase) in combination with the alkaline unwinding assay. Fe-NTA induced oxidative DNA damage in a time- and dose-dependent manner, yielding significant increases in Fpg-sensitive sites above background after incubation for 24 or 48 h with 500 and 250 microM respectively. At both time points the frequency of DNA base modifications exceeded the number of DNA strand breaks. In contrast, neither DNA strand breaks nor Fpg-sensitive sites were detected after treatment with Fe-citrate at concentrations up to 2 microM for 24 or 48 h; this inactivity of Fe-citrate was independent of the molar ratio of iron to ligand (1:1, 1:2, 1:10 or 1:20). The results indicate that the cellular damage induced by ferric iron depends strongly on the actual complex applied, possibly due to differences in the intracellular distribution, which in turn may affect the availability of iron for redox reactions at or in close proximity to the DNA.     

Glomerular permeability: in vivo tracer studies with polyanionic and polycationic ferritins

The influence of molecular charge on glomerular permeability to the globular ferritin molecule in vivo was investigated. Mice (Charles River CD strain) and rats (Munich-Wistar strain) were injected intravenously either with native anionic ferritin or various cationized derivatives with different isoelectric points (pI) and the kidneys were examined by electron microscopy. Native anionic ferritin was almost completely restricted from entry into the glomerular filter at the level of the endothelium and subendothelial layer of the glomerular basement membrane (GBM). Cationized derivatives penetrated the filter in increasing amounts depending on the pI of the tracer. Regardless of charge, all molecules that filtered through the lamina densa of the GBM and reached the subepithelial layer were completely restricted from entry into the urinary space at the level of filtration slits and appeared in phagosomes present in podocytes. Reduction of arterial pressure of cessation of renal blood flow did not influence the movement of ferritin molecules into the GBM. The results are consonant with physiological studies indicating charge dependent restriction of polyanion transport by the mammalian glomerulus. These tracer studies, in conjunction with cytochemical and biochemical evidence for the presence of polyanionic glycoproteins in the glomerular filter, suggest that glomerular restriction of plasma proteins occurs in part by a process similar to that which exludes negatively charged macromolecules in polyanionic gel systems.     

Equilibrium between sulfur and titanium in liquid iron

This investigation of liquid Fe-Ti-S alloys has involved experimental measurements of the titanium sulfide solubility product over the temperature range 1560 °C to 1640 °C. In addition, the sulfur-titanium interaction parameter was measured and the sulfide stoichiometry was determined. Using literature values for the sulfur and titanium self-interaction parameters, the solubility product for the equilibrium sulfide, TiS, was determined to be 0.411 at 1600 °C. The sulfur-titanium interaction parameter was determined to be −0.20 at 1600 °C. Comparisons with previously reported studies are presented.     

The interaction between radiation and adriamycin damage in mammalian cells

Interaction between radiation and Adriamycin damage reduced the width of the shoulder of the X-ray survival curve. This effect was found to persist for at least 24 hr after Adriamycin treatment. Adriamycin did not affect radiation damage when cells were treated either before two-dose fractionation or with the drug present between X-ray exposures. Adriamycin is unique in that its major effect on radiation response is to reduce the survival curve shoulder without affecting two-dose recovery. It is suggested that Adriamycin and radiation produce independent classes of damage that are expressed mutually for killing, with regard to the registration of sublethal radiation damage, but that repair of the latter is unaffected by Adriamycin.     

Relationship between grain

The relationship between the average mean grain boundary curvature,H, and the mean linear grain intercept, λ, has been experimentally determined for aluminum. The ratioH/λ ^{- 1} = 0.31 was found to remain constant throughout grain growth. This value yields a driving pressure for grain growth approximately three times smaller than that derived by conventional modeling and yields realistic results in models of particle- or pore-inhibited grain growth.     

Equilibria between cerium or neodymium and oxygen in molten iron

Autoradiographs show that there is an obvious reaction between Ce and Nd in liquid iron and the MgO/CaO crucible wall. For reaching the Ce-O, Nd-O equilibrium, a long melting period and the addition of rare earth elements (RE’s) in several batches were needed to ensure the full reaction between the RE’s in the melt and crucible wall. The dissolved Ce or Nd content in iron was measured by means of radioactive isotopes¹⁴¹Ce or¹⁴⁷Nd and electrolysis in the organic electrolyte. The oxygen activity was measured by solid electrolyte sensors made of ZrO₂(MgO) tube. The relationships between the equilibrium constants and the temperatures for reactions Ce₂O₃ (s) = 2[Ce] + 3[O], CeO₂ (s) = [Ce] + 2[O], and Nd₂O₃ (s) = 2[Nd] + 3[O], as well as the corresponding thermodynamic parameters, have been determined. Formerly Graduate Student at the University of Science and Technology Beijing     

Equilibria between rare earth elements and sulfur in molten iron

The equilibrium constants of Ce-S, La-S, and Nd-S in molten iron and the related interaction coefficients were determined experimentally and the following results obtained: K_CeS = 2.80 × 10^-6 e_S ^Ce = −1.88 K_LaS = 7.41 × 10^-7 e_S ^La= −1.51 K_NdS = 2.57 × 10^-6 e_Nd ^S= −1.51 In these experiments a radioactive isotope technique was used to determine the extremely low contents of the rare earth elements in the metal phase at equilibrium. In order to avoid errors caused by any partial inclusion of RE content of nonmetallic inclusions in the analytical results for the dissolved RE, the metal samples were electrolyzed in an organic electrolyte at low temperature, and the dissolved rare earth contents determined by measuring the radioactivity of the electrolyte. The dependence of the equilibrium values (concentration products) Ce-S on [pct C] in the system Fe-Ce-S-C was also determined. The interaction coefficient e_Ce ^C was determined to be −0.43. Earlier workers have obtained higher values for the Ce-S and La-S equilibrium constants than the present authors. Some explanation is offered for the difference.     

Relationship between internal calcium and outward current in mammalian ventricular muscle; a mechanism for the control of the action potential duration?

In sheep and calf ventricular bundles, increasing the internal calcium by increasing the frequency of voltage-clamping to plateau range potentials increased the time-independent outward current. This effect was more marked with higher [Ca]o, and was reduced if the Ca current blockers Verapamil or D 600 were used. 2. If the internal Ca was increased by the addition of cyanide and reduction of external sodium the outward current was also increased. The frequency-dependent increase in outward current also occurred in this Na-poor (12 mM) solution. 3. Tension measurement on the ventricular bundles showed that a Na-free solution with cyanide did not cause a contracture. On changing from Tyrode to a Na-free solution containing cyanide, and on changing back to Tyrode there was a potentiation of the twitch. 4. In Na-poor solution with cyanide, although no contracture was found, ECa was less positive, suggesting that under these circumstances Ca accumulates at the inner side of the membrane, but not around the myofibrils. 5. The prolongation of the action potential in Cl-free solution is frequency-dependent. A greater prolongation is seen at lower frequencies suggesting that Cl current is relatively more important for repolarization at lower frequencies of stimulation. 6. It is suggested that calcium at the inner side of the membrane sets the level of the background outward current. A feed-back mechanism on this basis is proposed for the control of the action potential duration. Various factors that could influence this basic mechanism are discussed.