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PubMed1984

Interaction of electron acceptors with the excited triplet state of Zn cytochrome c.

The decay rate of the excited triplet state of Zn cytochrome c was enhanced by electron acceptors including methyl viologen and ferric complexes of cyanide, oxalate, EDTA and cytochrome c at room temperature. Ferrous compounds were several orders of magnitude less effective than the respective ferric form in quenching the phosphorescence. In the presence of ferricytochrome c and ferricyanide the semilogarithmic plots of the decay curve showed an anomalous decay profile in which the rate of interaction appeared to accelerate after excitation. One explanation is that the quenching process was accelerated by a conformational change of the polypeptide chain around the excited triplet state porphyrin. Another explanation is that quenching occurs via an intermediate.

Animals↗
PubMed1987

A ferriprotoporphyrin IX-chloroquine complex promotes membrane phospholipid peroxidation. A possible mechanism for antimalarial action.

The effect of a ferriprotoporphyrin IX-chloroquine complex on phospholipid membranes was investigated on the basis of iron-induced lipid peroxidation using microsomal phospholipid liposomes. The ferriprotoporphyrin IX-chloroquine complex remarkably promoted peroxidative cleavage of unsaturated phospholipids in liposomes, compared with ferriprotoporphyrin IX alone. Neither the combination of protoporphyrin IX with chloroquine nor the combination of Fe3+-ADP with chloroquine promoted lipid peroxidation. DL-alpha-Tocopherol completely inhibited lipid peroxidation induced by the ferriprotoporphyrin IX-chloroquine complex.

Chloroquine↗
PubMed1989

DNA sequence-specific adducts of adriamycin and mitomycin C.

Adriamycin and mitomycin C were reduced by xanthine oxidase/NADH in the presence of a DNA template comprising a stable initiated ternary transcription complex derived from the lac UV5 promoter. Subsequent elongation of the transcription complex treated with mitomycin C revealed high levels of terminated transcripts one nucleotide prior to G residues on the coding strand (i.e. at X of XpC sequences of the non-coding strand). Lower levels of termination occurred with adriamycin, and these were also one nucleotide prior to G residues of the coding strand, but with greater sequence specificity since they were observed mainly at G of GpC sequences of the non-coding strand. The same sites were also observed with adriamycin in the absence of reducing conditions and the level of termination at these sites was enhanced up to 10-fold by Fe2+ and Fe3+, but not by Cu2+, Zn2+, Co2+ or Ni2+. These results suggest that an iron-adriamycin complex with DNA is highly sequence-specific and results in adducts, similar to those of mitomycin C, which can terminate the transcription process. Such a mechanism offers new insights into the possible mode of action of anthracyclines.

Base Sequence↗
PubMed1994

Enhancement of hydrogen peroxide-induced luminol-dependent chemiluminescence by neopterin depends on the presence of iron chelator complexes.

We have previously shown that neopterin, 6-D-erythro-trihydroxypropyl-pteridine, synthesized by human monocytes/macrophages upon stimulation by interferon-gamma, enhances toxicity of reactive oxygen at neutral or slightly alkaline pH (7.5), but not at acidic pH (below 6.5). In the present study, we explored in more detail the necessary requirements for neopterin to modulate the effects of hydrogen peroxide in a luminol-dependent chemiluminescence assay. We demonstrate that neopterin enhances hydrogen peroxide effects only in the presence of iron chelator complexes like iron-(III)- or iron-(II)-EDTA or iron-(III)-DTPA. Thus, iron chelator complexes together with neopterin may play an important role in macrophage-mediated effector mechanisms.

Biopterins↗
PubMed1996

Evaluation of the metal ion requirement of the human deoxyhypusine hydroxylase from HeLa cells using a novel enzyme assay.

Hypusine synthesis in the eukaryotic initiation factor 5A is a unique two-step posttranslational modification. After deoxyhypusine is generated by the deoxyhypusine synthase, the deoxyhypusine hydroxylase (EC 1.14.99.29) catalyzes the formation of mature hypusine. A rapid assay for monitoring the deoxyhypusine hydroxylase activity was established, employing the oxidative cleavage of the hypusyl residue and subsequent extraction of the generated aldehydes. As metal ion chelators have been reported to inhibit the deoxyhypusine hydroxylase, the mechanism of this inhibition and the effect of transition metal ions on enzyme activity were investigated. A ferric ion appears to be essential for enzymatic activity, the inhibition of which is entirely attributed to the metal ion binding capacity of the chelators.

Chelating Agents↗
PubMed1985

Influence of several perturbants on the rate of autoxidation of horse heart ferrocytochrome c.

The effect of several different types of perturbants and pH on the rate of autoxidation of horse heart ferrocytochrome c was investigated. The kinetic behavior is unique to each perturbant used. Rates of autoxidation followed first-order kinetics over the time span (0-180 min) studied. The Cl- and Br- anions exhibit an initial increase in the rate of autoxidation up to 100 mM, followed by a decrease in kinetics at 500 mM anion concentration. The ClO4- anion exhibits only an increase in the rate of autoxidation with increasing ionic strength, where as, propylurea, a hydrophobic perturbant, is not effective in altering the rate of autoxidation at equivalent concentrations. These studies suggest that the perturbations of the reduced form of cytochrome c in solution involve mainly non-specific solvent effects.

Animals↗
PubMed1994

Spectral analysis of Fe(III)-complex reduction by hemoglobin: possible mechanisms of interaction.

1. Hemoglobin is capable of electron transfer to Fe(III)-complexes of ATP, EDTA, NTA, and citrate leading to formation of reduced Fe(II) and its concurrent release from these chelating compounds as evident in the formation of a Fe(II)-Tris 2,2' bipyridine complex. 2. Multi-component analysis of kinetic spectra in the visible region (700-500 nm) has permitted a determination of the effect of various chelating molecules bound to Fe(III), pH, the effects of ionic strength, temperature, and the molecular nature of the Fe(III)-complex on reaction rates. 3. We have examined and compared the reactivities of normal adult hemoglobin A (alpha 2 beta 2) to reduce these Fe(III)-complexes and suggest possible mechanism(s) for the electron transfer process.

2,2'-Dipyridyl↗
PubMed1995

The cellular reactions to experimental intracerebral hemorrhage.

The resolution of an intracerebral hemorrhage can be measured by the occurrence of hemosiderin. Extravasation of blood elicits a cellular reaction in the adjacent surviving tissue where the lesion activates resident microglia and attracts many more phagocytes from the blood stream. The signals for this migration into the perifocal reactive zone are not fully understood but it is likely that proteins in the coagulated blood contribute to cellular activation. In order to study the role of plasma proteins in the pathogenesis of the perifocal reactive zone, intracerebral injections of either autologous whole blood (0.1 ml) or an equal volume of washed autologous red blood cells (RBC) in lactated Ringer's solution were made in adult rabbits. The amount of total iron was the same (30 micrograms). The cellular responses to the injections were studied by iron histochemistry and immunocytochemistry for ferritin, the ferritin repressor protein (FRP), the glial fibrillary acidic protein (GFAP), and the complement receptor CR3. Experimental hematomas resolved much more slowly after the injection of whole blood than after the injection of RBC. Qualitative microglial and astrocytic responses were quite similar. However, at 48 h, iron- and ferritin-reactive microglia were more numerous following the injection of whole blood. After injections of either type, ferritin-immunoreactive cells were more abundant than iron-positive cells. This observation implied that the biosynthesis of holoferritin protein and iron incorporation proceeded independently. Expression of CR3 on the surface of microglia was much more prominent after whole blood, suggesting a role of inactivated complement 3b in the attraction of additional phagocytes. Conversion to hemosiderin began at 5 days after the injection of either blood or RBC. The lesions caused initial destruction of astrocytes in the perifocal zone as judged by GFAP- and FRP-immunoreactivity. However, at 5 days, astrocytic processes reentered the perifocal zone and intermingled with microglia and macrophages. It is proposed that this contact between astrocytes and microglia reversed the uncoupling of ferritin biosynthesis and iron incorporation and initiated the storage of iron and formation of hemosiderin.

Animals↗
PubMed1990

Peroxidation in position C-6 of progesterone-3-ethanolimine is increased by the presence of enzymes generating oxygen radicals.

The generation of 6-oxygenated (6 beta-hydroxy, 6 beta-hydroperoxy, and 6-oxo) progesterone derivatives during the hydrolysis of progesterone-3-ethanolimine has been shown to be increased in the presence of xanthine/xanthine oxidase. The combination of xanthine/xanthine oxidase with other enzymes and/or reagents that catalyze transformation (or formation) of oxygen radicals suggested that the most likely oxygen species participating in the 6-oxygenation was the protonated acid of the superoxide anion, i.e., the hydroperoxy radical. The suggestion was further supported by experiments with oxygen scavengers. However, the data presented do not rule out a radical propagation reaction since the steroid compound used may be more reactive than the scavengers tested. A stimulation of 6-oxygenation of progesterone-3-ethanolimine by NADPH-supplemented rat liver microsomes was found. This reaction was inhibited by the only oxygen scavenger (reduced glutathione) found to be effective in the xanthine/xanthine oxidase experiments. The similarities between the two oxygenation systems may implicate a mechanism for 6 beta-hydroperoxidation of 3-oxo-4-ene steroids in rat liver microsomes.

Animals↗
PubMed1987

The effect of di- and trivalent iron on the intestinal absorption of aluminum in rats.

The effect of iron (Fe) on the intestinal absorption of aluminum (A1) was studied in an in situ perfusion system of rat small intestine in combination with systemic and portal blood sampling. The gut was perfused with media containing 0.0, 10.0, 15.0, 20.0, and 25.0 mmol/liter Al chloride and 5 mmol/liter Fe(II) or Fe(III) chloride at pH 3.0. Neither luminal disappearance nor intestinal absorption of A1 were affected by Fe(III). Fe(II), however, enhanced luminal disappearance and reduced absorption of Al.

Aluminum↗
PubMed1995

Structure-function relationships for a new series of pyridine-2-carboxaldehyde thiosemicarbazones on ribonucleotide reductase activity and tumor cell growth in culture and in vivo.

The synthesis of a new series of pyridine-2-carboxaldehyde thiosemicarbazones (HCTs) that have amino groups in the 3- and 5-positions has allowed the comparison of the structure/function relationships with regard to inhibition of ribonucleotide reductase activity, L1210 cell growth in culture and L1210 leukemia in vivo. 3-Aminopyridine-2-carboxaldehyde thiosemicarbazones are more active than the corresponding 3-hydroxy-derivatives. The 3-amino-2-pyridine carboxaldehyde thiosemicarbazones were also more active then the 5-amino-2-carboxaldehyde thiosemicarbazones in inhibiting ribonucleotide reductase activity and L1210 cell growth in culture and in vivo. N-Acetylation of the 3-amino derivative resulted in a compound that was much less active both in vitro and in vivo; N-acetylation of the 5-amino derivative did not alter the in vitro inhibitory properties, but did eliminate the antitumor properties in vivo. When the most active HCTs were studied in more detail, it was found that the incorporation of [3H]thymidine into DNA was inhibited completely without the inhibition of [3H]uridine incorporation into RNA. Further, the conversion of [14C]cytidine to deoxycytidine nucleotides and incorporation into DNA was inhibited by the HCTs without an effect on the incorporation of cytidine into RNA. These data support the conclusion that ribonucleotide reductase is the major site of action of these HCTs. The 3-aminopyridine-2-carboxaldehyde thiosemicarbazones emerge as strong candidates for development for clinical trials in cancer patients.

Acetylation↗
PubMed1980

Epinephrine and other activators of prostaglandin endoperoxide synthetase can reduce Fe3+-heme to Fe2+-heme.

In view of recent evidence that activation of prostaglandin endoperoxide synthetase by lipid peroxides may relate to the ability of such peroxides to reduce heme, we tested other activators of this enzyme. Epinephrine, norepinephrine, ascorbic acid and tryptophan were all found to reduce Fe3+-heme to Fe2+-heme, though tryptophan was considerably weaker than the others. We suggest that reduction of heme by these compounds might account for their ability to reduce the lag phase on addition of substrate to the enzyme. Epinephrine was assessed for its effects on the lag phase in activation of soybean lipoxygenase and was found to cause a similar reduction of the lag phase of this related enzyme. These findings support the concept that reduction of Fe3+-heme to Fe2+-heme is critical to activation of both the prostaglandin endoperoxide synthetase and soybean lipoxygenase enzymes, and that mechanisms involved in regulation of the valence of iron are important for regulating enzyme activity.

Ascorbic Acid↗
PubMed1990

Thermochromism of heme adducts of Glycera hemoglobin and some other monomeric heme proteins.

The thermally induced difference spectra of myoglobin (Mb) and Glycera dibranchiata hemoglobin (Hbm) derivatives and of cytochrome-c were recorded between 4 degrees and 30 degrees C in the 390-750 nm range. Thermodynamic parameters were estimated and upper and lower temperature limiting spectra were deduced for the various heme protein derivatives' equilibria. The effective iron d-electron population divides the hemes broadly into two different groups of behavior type. In the first group, Hbm(III)N3, Hbm(III), Mb(III)(H2O), and Cytc(III) show equilibria between two spin states. The weakest coupling between the heme and the globin occurs among the second group, for Hbm(II)CO and Mb(II)CO, which in the higher temperature limit undergoes averaging of the carbonyl tilt, while an axially elongated geometry is probably accessed for Hbm(II)NO and Mb(II)NO. Examples of the less common situation of increased absorption intensity and/or low-spin states at higher temperature were found in both groups. In the case of the methyl thioglycolate low-spin adducts of Hbm(III), an acid/base equilibrium involving thioglycolate deprotonation occurs. Apparent enthalpy-entropy compensation is exhibited by all these heme derivatives, and it is suggested that the delta H degrees and delta S degrees values relate to the intimacy of coupling between the heme structure and the solvent-dependent microconformation of the globin.

Animals↗
PubMed1990

The cyclic voltammetric study of iron-tallysomycin in the absence and presence of DNA.

Cyclic voltammetric studies on iron-tallysomycin complexes have been conducted with and without the presence of calf thymus DNA. Fe(II)-TLM samples exhibit a cyclic voltammogram with only a reduction peak at -230 +/- 5 mV vs Ag/AgCl. The addition of DNA substrate causes the shift of this reduction peak to -140 +/- 10 mV vs Ag/AgCl. This large shift in the positive direction implies that the regeneration of Fe(II)-TLM through the reduction of Fe(III)-TLM is facilitated with the aid of DNA. It also implies that the metal-binding/oxygen-activation domain may be directly involved in the formation of iron-tallysomycin-DNA ternary complex. Air oxidation of Fe(II)-TLM produces an activated intermediate with the following CV characteristics, Ipc/Ipa = 0.90; delta E = 65 mV; Ereduction peak = -100 mV vs Ag/AgCl. Addition of DNA abolishes the redox peaks of this voltammogram, signifying inactivation of the activated species through reaction with substrate. Air oxidation of preformed Fe(II)-TLM-DNA complex did not give a discernable cyclic voltammogram, nor did preformed Fe(III)-TLM and Fe(III)-TLM-DNA samples.

Animals↗
PubMed1990

Effect of hydration in metHb: reversible changes monitored by ESR of iron.

The dehydration of human and bovine methemoglobins was monitored using ESR spectroscopy of the iron signal. The interconversion of the Fe(III) signal between the high spin form (at g approximately 6) in solution and low spin form (at g approximately 2) was quantitatively studied as a function of hydration. The dehydration process leads also to a loss of paramagnetism resulting in the appearance of about 40% Fe(II) below 0.40 grH2O/grHb. The remaining 60% of Fe(III) ESR signal is distributed as the residual high spin form (at g approximately 6, 5%) and low spin form (hemichromes H and P, 55%). The formation of hemichrome P was explained as resulting from the coordination of the cysteine residue at beta 93 with the iron atom which follows the rupture of the proximal histidine bond. Experiments with hemoglobins where the sulphur atom of cysteine beta 93 was blocked (N-ethylmaleimide) did not showed the hemichrome P, confirming the involvement of the sulphur atom. This implies that the dehydration process induces displacements and torsion of the F helix, drastically changing the iron coordination at proximal site. In agreement with this proposition the Fe(II) symmetry is pentacoordinated with the disrupted bond to the proximal histidine at fifth coordination. This is also supported by ESR experiments with nitrosyl complex at low hydrations. All conformational changes were reversibly modulated by hydration degree and partially by lyophilization rate. A one-cycle dehydration of bovine hemoglobin followed by solubilization shows 100% reversibility of hemichrome P. Increasing the number of cycles of dehydration-hydration reduces the reversibility degree. With three cycles a reversibility of 70%-75% is observed. The level of 0.40 grH2O/grHb was the critical hydration for the molecules to return to aquo met form and correspond also to a minimal water content necessary to cover all protein surface as obtained from other techniques.

Animals↗
PubMed1990

Effect of ascorbic acid, sodium citrate, sodium bicarbonate, and their combination effect on the binding of 59Fe2+ and 59Fe3+ to plasma membrane of lactating mouse mammary gland.

Isolated plasma membranes of lactating mouse mammary gland were treated with different concentrations of ascorbate, sodium citrate, sodium bicarbonate, and combinations of them (from 16 x 10(-10) to 4 x 10(-6) moles/L) and studied for the binding of 59Fe2+ and 59Fe3+ at pH 7.4. The results show that the Fe3+ form of iron is under a greater influence of anions used in these experiments. The Fe2+ form of iron is weakly bounded and affected. It is suggested that the form with a greater positive electric charge is more effectively bound to the receptors in plasma membranes.

Animals↗