Binding Of Fe3 Research Articles

Inhibition and inactivation of NADH-cytochrome c reductase activity of bovine heart submitochondrial particles by the iron(III)-adriamycin complex

The NADH-cytochrome c reductase activity of bovine heart submitochondrial particles was found to be slowly (half-time of 16 min) and progressively lost upon incubation with the Fe2(+)-adriamycin complex. In addition to this slow progressive inactivation seen on incubation, a reversible fast phase of inhibition was also seen. However, if EDTA was added to the incubation mixture within 15 s, the slow progressive loss in activity was largely preventable. Separate experiments indicated that EDTA removed about one-half of the iron from the Fe2(+)-adriamycin complex in about 40 s. These results indicated the requirement for iron for the inactivation process. Since the Vmax. for the fast phase of inhibition was decreased by the inhibitor, the inhibition pattern was similar to that seen for uncompetitive or mixed-type inhibition. The direct binding of both Fe3(+)-adriamycin and adriamycin to submitochondrial particles was also demonstrated, with the Fe3(+)-adriamycin complex binding 8 times more strongly than adriamycin. Thus binding of Fe3(+)-adriamycin to the enzyme or to the inner mitochondrial membrane with subsequent generation of oxy radicals in situ is a possible mechanism for the Fe3(+)-adriamycin-induced inactivation of respiratory enzyme activity.

Cation Migration in Smectite Minerals: Electron Spin Resonance of Exchanged Fe3+ Probes

AbstractThe migration of interlayer Fe3+ cations into the structure of heated montmorillonite and Laponite has been studied by electron spin resonance (ESR), Mössbauer spectroscopy, and magnetic susceptibility measurements. The intensity of the ESR signal corresponding to interlayer Fe3+ in air-dried montmorillonite and Laponite increased linearly as the amount of interlayer Fe3+ increased. Changes in the spectra after thermal treatment indicate that Fe3+ cations migrated into the pseudohexagonal cavities of dehydrated montmorillonite and Laponite. The electrostatic interaction between the Fe3+ and the oxygen atoms defining the entrance to these cavities and the proton of the structural OH groups at the bottom of the cavities differ for the two smectites. Ferric cations were apparently bound more strongly within the pseudohexagonal cavities of the dehydrated montmorillonite than within the cavities of Laponite, because the montmorillonite did not rehydrate after heating. The differences in the binding of Fe3+ cations within the pseudohexagonal cavities of montmorillonite and Laponite were probably due to variations in the ability of the protons of the structural OH groups to reorient. An additional electronic interaction occurred in the heated Laponite, in which small cations were able to promote the formation of structural defects, which gave rise to a sharp ESR signal at g = 2.00. No evidence for the penetration of Fe3+ cations into the vacant octahedral sites of montmorillonite was found.

Binding of iron to human red blood cell membranes.

The binding of Fe3+ to red cell membranes was studied in a system in which lipid peroxidation was proportional to Fe3+ concentration. Binding of Fe3+ was evaluated by labeling with 59FeCl3 and measurement of NMR water-proton relaxation times. Labeling with 59Fe showed that 95% of the Fe3+ was membrane bound at 100 microM FeCl3 in a 1.5 mg protein/ml membrane suspension. Both spin-lattice (T1) and spin-spin (T2) relaxation times decreased with increasing Fe3+ concentration. Addition of red cell membrane suspensions largely prevents the Fe3+ effect on relaxation times. Charge transfer to Fe3+ may occur at the membrane binding site with resultant decrease in the Fe3+ effect on water-proton relaxation times. These studies support the hypothesis that Fe3+ binds to the membrane and generates free radicals at the binding site.

The iron chelators desferrioxamine and 1-alkyl-2-methyl-3-hydroxypyrid-4-ones inhibit vascular prostacyclin synthesis in vitro.

The iron chelators desferrioxamine (DFO), 1,2-dimethyl(L1)-, 1-ethyl-2-methyl(L1NEt)- and 1-propyl-2-methyl(L1NPr)-3-hydroxypyrid-4-ones inhibited rat aortic prostacyclin (PGI2) synthesis in vitro (rank order of potency: DFO greater than L1 greater than L1NEt greater than L1NPr) when stimulated with adrenaline, arachidonate and the Ca2+ ionophore A23187. The inhibitory action of the chelators was blocked by Fe3+ and Al3+ and reversed by washing and H2O2, but not by ascorbate. These data suggest that iron chelators inhibit prostanoid synthesis in intact tissue through the removal or binding of Fe3+ linked to cyclo-oxygenase. These iron chelators may be of therapeutic value in the treatment of inflammatory and other diseases via two mechanisms: (1) the inhibition of pro-inflammatory prostanoid synthesis and (2) the inhibition of toxic-free-radical generation by cyclo-oxygenase.

Kinetics and Equilibrium of Binding of Fe3+ by a Fulvic Acid: A Study by Stopped Flow Methods

The first report of a rate of binding of a metal ion (Fe3+) by a soluble fulvic acid is derived from stopped flow measurements. The rate of complex formation is normal in Wilkins' sense and similar to that for sulfosalicylic acid. Dissociation is slow (t1/2 > 10 s). The binding of Fe3+ by the fulvic acid in acid solution, pH = 1–2.5, was investigated by kinetic analysis in which the reaction of free Fe3+ with sulfosalicylic acid was followed by stopped flow spectrophotometry on a time scale short compared to release of Fe3+ by fulvic acid. Conditional equilibrium constants found were 1.5 ± 0.3 × 104 at pH = 1.5 and 2.5, and 2.8 ± 0.3 × 103 at pH = 1.0 at 25 °C (ionic strength 0.1).

Differences in the protein fluorecence of the two iron(III)-binding sites of ovotransferrin.

1. Changes in the tryptophan fluorescence and the visible absorption spectrum resulting from the combination of apo-ovotransferrin with Fe3+, F,E2+, Cu2+, Zn2+, Mn2+, and Cd2+were measured. 2. As expected for a radiationless transfer of electronic excitation energy, only the ions Fe3+, Fe2+and Cu2+, which gave complexes with large extinctions between 300 and 370nm, resulted in large decreases in trytophan fluorescence. 3. The decrease in protein fluorescence was non-linear with increasing occupancy of the Fe3+ -and Cu2+ - binding sites. The decrease in fluorescence on binding of Fe3+ was biphasic and showed that the two metal-binding sites were being occupied sequentially at pH7.4-8.4. The first site reacted with Fe3+ instantaneously, the second was occupied over a minute. 5. The nonidentity of the two sites was also demonstrated by the preparation of a stable hybrid containing both Cu2+ and Zn2+.h Cu2+ and Zn2+

Binding of Iron and Copper to Bovine Heart Mitochondria

Bovine heart mitochondria were found to bind large amounts of Cu2+, Cu+, Fe2+, and Fe3+ in a rapid, energy-independent reaction. Binding was more than 80% complete within 15 s (the shortest time tested). To prevent disproportionation of Cu+ to Cu2+ and Cu0, a cuprous-acetonitrile-perchlorate complex was used. Fe3+ was added as the 8-hydroxyquinoline or the citrate derivative. Of Cu2+, Fe2+, and Fe3+, 1.5 to 2.5 µmoles per mg of protein could be bound in the absence of phosphate, while as much as 4 to 6 µmoles per mg of protein were bound in the presence of phosphate. A Cu2+- or Fe2+-dependent Pi uptake was observed with cation to Pi uptake ratios of 1.5 to 1.8, suggestive of the formation of Cu3(PO4)2 or Fe3(PO4)2. Cu+ binding, however, was limited to about 120 nmoles per mg of protein and a Km value of 0.42 m m was obtained. The binding of copper was inhibited by chelating agents. Bound copper was not removed by washing with sucrose, respiratory inhibitors, detergents, or mercurials, but was removed by chelating agents having a strong affinity for copper. Some of the Cu2+ was converted to Cu+ on being bound. Iron, once bound, was essentially attached in an irreversible manner, since it was not removed by various chelating agents and other additives. However, the initial iron binding was sensitive to these additives, which suggests that iron may initially bind in a reversible manner. Cu2+ and Cu+ binding was only slightly inhibited by Ca2+, Sr2+, Mg2+, Mn2+, and the inhibition was not increased by adding phosphate or a source of energy. Zn2+, Ag+, and especially Hg2+, were more potent inhibitors of copper-binding than the above cations. There was no inhibition by monovalent cations. No competition was observed between copper and iron. In fact, copper was slightly stimulatory to the binding of iron, while iron was slightly stimulatory to the binding of copper. Thus, copper and iron do not bind to the same locus. The binding of Fe3+ was insensitive to Ca2+, Sr2+, Zn2+, or K+ in the presence or absence of Pi, or in the presence of an energy source. The binding of Fe2+ was inhibited by the monovalent cations Li+, Na+, and K+. Divalent cations, such as Mn2+, Ca2+, Sr2+, and Mg2+ were about 25 to 40% inhibitory toward Fe2+ binding at concentrations twice that of Fe2+. Zn2+ and Hg2+ were more potent inhibitors of Fe2+ binding (70 to 80% inhibition) than the other divalent cations. It is concluded that Cu+ and Cu2+ may bind to the sites implicated by others as binding Hg2+ and Zn2+. Fe2+ and Fe3+ bind to sites that are different than the sites which bind Cu+ and Cu2+ and the sites which bind Ca2+.

Binding of ferric ions to nuclei and other tissue sites in sections stained for sulfated mucosubstances by the high-iron diamine method.

Binding of Fe3+ occurred in nuclei and several other sites when tissue sections, after a prior staining by the high-iron diamine (HID) method for sulfomucins, were immersed for 1 hr in 0.06 N HCl containing 1% potassium ferrocyanide (Prussian blue reaction). Apparently Fe3+, which is derived from FeCl3 present in the HID dye bath, unites directly with these tissue components, although one cannot exclude the possibility that iron is first bound to colorless diamine complexes and then to tissues. The visualization of Fe3+ by ferrocyanide provides a simple way of obtaining a suitable nuclear stain combined with general counters taming for the HID method.

Metal-ion binding of human transferrin

1.1. The effects of pH and different buffer systems have been studied on the binding of Fe3+ to transferrin.2.2. The effect of pH on the binding of Ca2+, Co2+, Cu2+ and Zn2+ to transferrin was examined. The sites of binding are not those for Fe3+, although Cu2+ may include these sites.3.3. Experiments are described which support the hypthesis that tyrosyl residues are part of the Fe3+ binding sites.