Superoxide-independent reduction of vanadate by rat liver microsomes/NAD(P)H: vanadate reductase activity.

It has been reported that vanadate-stimulated oxidation of NAD(P)H by microsomal systems can proceed anaerobically, in contrast to the general notion that the oxidation proceeds exclusively by an O(2-)-dependent free radical chain mechanism. The current study indicates that microsomal systems are endowed with a vanadate-reductase property, involving a NAD(P)H-dependent electron transport cytochrome P450 system. Our ESR measurements demonstrated the formation of a vanadium(IV) species in a mixture containing vanadate, rat liver microsomes, and NAD(P)H. This vanadium(IV) species was identified as the vanadyl ion (VO2+) by comparison with the ESR spectrum of VOSO4. The initial rate of vanadium(IV) formation depends linearly on the concentration of microsomes. The Michaelis-Menten constants were found to be: km = 1.25 mM and Vmax = 0.066 mumol (min)-1 (mg microsomes)-1, respectively. Pretreatment of the microsomes with carbon monoxide or K3Fe(CN)6 reduced vanadium(IV) generation, suggesting that the NAD(P)H-dependent electron transport cytochrome P450 system plays a significant role in the microsomal reduction of vanadate. Measurements under argon or in the presence of superoxide dismutase caused only minor (less than 10%) reductions in vanadium(IV) generation. The VO2+ species was also detected in NAD(P)H oxidation by fructose plus vanadate, a reaction known to proceed via an O(2-)-mediated chain mechanism. However, the amount of vanadium(IV) generated by this reaction was an order of magnitude smaller than that by the microsomal system and was inhibitable by superoxide dismutase, affirming the conclusion that the microsomal/NAD(P)H system is endowed with the (O(2-)-independent) vanadium(V) reductase property.     

Cobalt(II) and μ-oxodiiron(III,IV) complexes of salen analog with aromatic thioether pendant group,N, N′-disalicylidene-2-methyl-4-(2-methylthiophenyl)- 1,2-butanediamine

A pentadentate salen analog containing a thioether group in the pendant tail, N,N′-disalicylidene-2- methyl-4-(2-methylthiophenyl)- 1,2-butanediamine, has been synthesized. The cobalt(II) complex of this ligand retains a planar configuration free from the coordination of the pendant group at room temperature but adopts a square-pyramidal configuration with the thioether at the apex near liquid nitrogen temperature. The iron complex obtained with this ligand is shown to be a μ-oxodiiron(III, IV) complex comprised of high-spin iron(III) and low-spin iron(IV), based on cryomagnetic data (80–300 K), ESR, and M:ossbauer spectra. An antiferromagnetic spin-exchange interaction (J = − 13.0 cm ⁻¹) operates between the metal ions.     

A spectroscopic and electrochemical study of the interaction between copper (II) glycylglycyl-L-histidine-N-methylamide and iron (III) tetra-p-sulfophenylporphine

A binuclear complex has been produced by the reaction of an iron porphyrin (sodium tetra-p-sulfophenylporphine iron (III)-FeTPPS) with a copper metallo-tripeptide (copper (II) glycylglycyl-L-histidine-N-methylamide-CuGGH) in aqueous solution. The system has been characterized by electron spin resonance (ESR) spectroscopy, optical absorption spectroscopy, and electrochemical methods. Room-temperature ESR spectra of the copper complex and low-temperature ESR spectra of the iron porphine provide evidence for the formation of a binuclear complex. These findings are supported by absorption spectroscopy and electrochemical studies, and lead to a value of ca. 2 X 10(-3) M-1 (at room temperature) for the equilibrium constant for complex formation. The relevance of this system to the enzymic active site of mammalian cytochrome c oxidase is discussed.     

A possible model of hemoprotein-fatty acid peroxide complex demonstrated by electron spin resonance

Coordination reaction between linolenic-acid-hydroperoxide (LHPO) and chloro(5, 10, 15, 20-tetraphenyl)-porphyrinato iron (III), Fe(III)TPPCl, was investigated by means of ESR. ESR spectra of the ferric low-spin complex (g1 = 2.336, g2 = 2.174 and g3 = 1.929) was recorded for the mixture prepared by mixing Fe(III)TPPCl and LHPO at -78 degrees C in the presence of alkaline reagent. ESR line width of complex was broadened when 17O2 labeled LHPO was used for ESR measurement. In terms of the g-parameters of the ferric low-spin species, this complex was concluded to be Fe(III)TPP(-OCH3)(-OO-linolenic acid) type complex.     

Bohr-effect and pH-dependence of electron spin resonance spectra of a cobalt-substituted monomeric insect haemoglobin

The monomeric haemoglobin IV from Chironomus thummi thummi (CTT IV) exhibits an alkaline Bohr-effect and therefore it is an allosteric protein. By substitution of the haem iron for cobalt the O2 half-saturation pressure, measured at 25 degrees C, increases 250-fold. The Bohr-effect is not affected by the replacement of the central atom. The parameters of the Bohr-effect of cobalt CTT IV for 25 degrees C are: inflection point of the Bohr-effect curve at pH 7.1, number of Bohr protons -- deltalog p1/2 (O2)/deltapH = 0.36 mol H+/mol O2 and amplitude of the Bohr-effect curve deltalogp1/2 (O2) = 0.84. The substitution of protoporphyrin for mesoporphyrin causes a 10 nm blue-shift of the visible absorption maxima in both, the native and the cobalt-substituted forms of CTT IV. Furthermore, the replacement of vinyl groups by ethyl groups at position 2 and 4 of the porphyrin system leads to an increase of O2 affinities at 25 degrees C which follows the order: proto less than meso less than deutero for iron and cobalt CTT IV, respectively. Again, the Bohr-effect is not affected by the replacement of protoporphyrin for mesoporphyrin or deuteroporphyrin. The electron spin resonance (ESR) spectra of both, deoxy cobalt proto- and deoxy cobalt meso-CTT IV, are independent of pH. The stronger electron-withdrawing effect by protoporphyrin is reflected by the decrease of the cobalt hyperfine constants coinciding with gparallel = 2.035 and by the low-field shift of gparallel. The ESR spectra of oxy cobalt proto- and oxy cobalt meso-CTT IV are dependent of pH. The cobalt hyperfine constants coinciding with gparallel - 2.078 increase during transition from low to high pH. The pH-induced ESR spectral changes correlate with the alkaline Bohr-effect. Therefore, the two O2 affinity states can be assigned to the low-pH and high-pH ESR spectral species. The low-pH form (low-affinity state) is characterized by a smaller, the high-pH form (high-affinity state) by a larger cobalt hyperfine constant in gparallel. The correlation of the cobalt hyperfine constants of the oxy forms with the O2 affinities is discussed for several monomeric haemoglobins. The Co-O-O bond angle in cobalt oxy CTT IV is characterized by an ozonoid type of binding geometry and varies little during the pH-induced conformation transition. Due to the lack of the distal histidine in CTT IV no additional interaction via hydrogen-bonding with dioxygen is possible; this is reflected by the cobalt hyperfine constants.     

The complex formation of copper(II) with GHL and HSA

The formation constants for complexes of copper(II) with GHL have been determined by means of pH titrations and ESR spectroscopy in aqueous solutions. GHL has an extremely high affinity for copper(II) and forms very stable 1:1 complexes and a comparatively weak 1:2 complex. The ? amino group of GHL seems not to be involved in complex formation as can be deducted from both equilibrium constants and ESR spectroscopy. The ternary system copper(II)-GHL-HSA was investigated by ESR spectroscopy and optical absorption spectroscopy in aqueous solution at physiological pH (7.4). At equimolar concentrations, copper(II), HSA and GHL form a ternary complex.     

First evidences of the formation of a vanadyl(IV) complex of bleomycin

Results of visible/ultraviolet and infrared spectroscopic measurements, as well as chemical evidence are presented which support the formation of a 2:1 bleomycin-VO2+ complex. The information obtained also allows some considerations concerning the probable coordination sphere of the vanadyl ion.     

Synthesis and insulinomimetic activities of novel mono- and tetranuclear oxovanadium(IV) complexes with 3-hydroxypyridine-2-carboxylic acid

Two chargeless VO(IV) complexes with 3-hydroxypyridine-2-carboxylic acid (H2hpic), [VO(Hhpic-O,O)(Hhpic-O,N)(H2O)].3H2O (1) and the cyclic tetramer [(VO)4(mu-(hpic-O,O',N))4(H2O)4].8H3O (2), have been synthesized and characterized by elemental analysis, mass, infrared, electronic absorption, electron spin resonance (ESR) spectroscopies, and X-ray crystallography. Their coordination structures are similar to each other (and 1 is readily transformed into 2), but are quite different from that of bis(pyridine-2-carboxylato)oxovanadium(IV). The magnetic susceptibility of 2 indicates the presence of a weak ferromagnetic intramolecular interaction between the V atoms at low temperature, in addition to a weak antiferromagnetic intermolecular interaction. The ESR signal of 2 was broad, while 1 showed an eight-line hyperfine splitting pattern due to coupling of the unpaired electron with the 51V nucleus (I=7/2). The ESR spectrum and cyclic voltammogram of 2 clearly show that the cyclic tetramer remains intact in solution. The insulinomimetic activity of 1 and 2 was evaluated by means of in vitro measurements of the inhibition of free fatty acid release from epinephrine-treated isolated rat adipocytes. While 1 exerted higher insulinomimetic activity than VOSO4, the activity of 2 was significantly lower than that of VOSO4. Hence 2 appears to retain its cyclic structure during the in vitro test. These results indicate that the rational ligand design for VO complexes might be a promising approach to obtain superior insulinomimetic activity.     

Crystallization of the lectin IV of Griffonia simplicifolia and its complexes with the Lewis b and Y human blood group determinants

Single crystals of the lectin IV from Griffonia simplicifolia have been grown in the tetragonal crystal system. The space group is P4(2)2(1)2 with a = 78.95(5) A and c = 89.01(2) A, and there is one subunit of the dimeric glycoprotein in the crystallographic asymmetric unit. The crystals diffract to at least 2.5 A d spacings and are stable in the x-ray beam for 3 weeks. Crystals of the complex with the Lewis b (Leb) and Y human blood group determinants as the methyl glycosides, alpha-L-Fuc(1----2)beta-D-Gal(1----3)[alpha-L-Fuc(1----4)]beta-D-GlcNAc-OMe (where Fuc is fucose and -OMe is methoxy) and alpha-L-Fuc(1----2)beta-D-Gal(1----4)[alpha-L-Fuc(1----3)]-beta-D-GlcNAc- OMe, respectively, have also been grown and found to be isomorphous with the native lectin. Crystals have also been obtained with several derivatives of the Lewis b-OMe tetrasaccharide including that which has the 6-hydroxyl of the beta-D-GlcNAc unit replaced by iodine. In the latter case, the presence of the iodine atoms was established.     

DNA interaction and nucleotide sequence cleavage of copper-streptonigrin

The copper-accelerated DNA binding and cleavage of streptonigrin have been investigated by 1H-NMR, ESR spectrometry and nucleotide sequence analysis. In the DNA breakage by the streptonigrin-Cu(II)-NADPH system, the somewhat preferred cleavage sites were several cytosine bases adjacent to purine bases such as GCGG(5'----3'), ACGC(5'----3') and GGCG(5'----3') sequences. The proton chemical shifts for the streptonigrin-Cu(I)-poly(dA-dT) complex demonstrated the interaction between the pyridine ring of the drug and the purine bases of the nucleic acid. Indeed, the temperature profile of adenine H-2 proton clearly showed the Tm to shift from 70 degrees C in the binary streptonigrin-poly(dA-dT) system to 75 degrees C in the ternary streptonigrin-Cu(I)-poly(dA-dT) system. The interaction of the streptonigrin-Cu(II) complex with DNA also induced the apparent change of ESR parameters. The tricyclic phenanthidium ring system including the copper chelate ring appears to significantly contribute to the present DNA interaction and cleavage of copper-streptonigrin.     

Electron spin resonance spectra of penta- and hexacoordinated nitrosyl iron protoporphyrin IX complexes

Electron spin resonance (ESR) spectra of frozen aqueous solutions of NO · haem · base complexes and NO · haem intercalated into dodecyl sulfate micelles have been measured at 77 K and analyzed for the hyperfine components of ¹⁵NO,¹⁴N-base, ¹⁴N-pyrroles and ⁵⁷Fe which coincide with the principal directions of the g tensor. The influence of the basicity of the nitrogen base on the spin distribution and geometry of the Fe-N-O grouping has been demonstrated by replacing imidazole for pyridine and by comparing the ESR spectra with those obtained for the monomeric insect haemoglobin CTT IV.The comparison of the hyperfine parameters described for the so-called pentacoordinated nitrosyl complex of CTT IV with those of the NO · haem intercalated into detergent micelles has furnished evidence that the ESR spectrum of this conformation state of haemoglobin has to be definitely assigned to a pentacoordinated nitrosyl complex.The a_zz values increase with the following orders: CTT IV (2.98 mT) < imidazole complex (3.04mT) < pyridine complex (3.15mT) for ¹⁵NO, and pyridine complex (0.59 mT) < imidazole complex (0.67 mT) < CTT IV (0.70 mT) for the ¹⁴N-base. This result is in conformity with an increase of the donor and the acceptor strengths of the nitrogen base in trans-position to ¹⁵NO. The a_yy and a_xx components of ¹⁵NO and the ¹⁴N-base are strongly nonequivalent in the nitrosyl haemoglobin CTT IV, and less nonequivalent in the NO · haem · pyridine complex, indicating bending of the Fe-N-O grouping. The hyperfine components of the axial ligands coinciding with the x and y component of the g tensor are nearly equal for the NO · haem · imidazole complex.     

The first spectroscopic model for the S1 state multiline signal of the OEC

The parallel-mode electron paramagnetic resonance (EPR) spectrum of the S(1) state of the oxygen-evolving complex (OEC) shows a multiline signal centered around g=12, indicating an integer spin system. The series of [Mn(2)(2-OHsalpn)(2)] complexes were structurally characterized in four oxidation levels (Mn(II)(2), Mn(II)Mn(III), Mn(III)(2), and Mn(III)Mn(IV)). By using bulk electrolysis, the [Mn(III)Mn(IV)(2-OHsalpn)(2)(OH)] is oxidized to a species that contains Mn(IV) oxidation state as detected by X-ray absorption near edge spectroscopy (XANES) and that can be formulated as Mn(IV)(4) tetramer. The parallel-mode EPR spectrum of this multinuclear Mn(IV)(4) complex shows 18 well-resolved hyperfine lines center around g=11 with an average hyperfine splitting of 36 G. This EPR spectrum is very similar to that found in the S(1) state of the OEC. This is the first synthetic manganese model complex that shows an S(1)-like multiline spectrum in parallel-mode EPR.     

Synthesis,structural characterization and in vitro cytotoxicity of organotin(IV) derivatives of heterocyclic thioamides, 2-mercaptobenzothiazole, 5-chloro-2-mercaptobenzothiazole, 3-methyl-2-mercaptobenzothiazole and 2-mercaptonicotinic acid

Five new organotin(IV) molecules with the heterocyclic thioamides; 2-mercaptobenzothiazole (Hmbzt), 5-chloro-2-mercaptobenzothiazole (Hcmbzt), 3-methyl-2-mercaptobenzothiazole (mmbzt) and 2-mercaptonicotinic acid (H(2)mna) of formulae [(n-C(4)H(9))(2)Sn(mbzt)(2)] (1), [(C(6)H(5))(2)Sn(mbzt)(2)] (2), [(CH(3))(2)Sn(cmbzt)(2)].1.7(H(2)O)] (3), [(n-C(4)H(9))(2)SnCl(2)(mmbzt)(2).(CH(2)Cl(2))] (4) and [[(C(6)H(5))(3)Sn](2)(mna).[(CH(3))(2)CO]] (5) have been synthesized and characterized by elemental analysis, 1H-, 13C-NMR, FT-IR and M?ssbauer spectroscopic techniques. Crystal structures of molecules 1, 3 and 5 have been determined by X-ray diffraction at 173(1) K (1 and 5) and 293(2) K (3). Compound 1 C(22)H(26)N(2)S(4)Sn, is monoclinic, space group C2/c, a=44.018(2), b=8.8864(5), c=12.8633(7) A, beta=104.195(5) degrees, Z=8. Compound 3 is also monoclinic, space group P2(1)/c and a=17.128(2) A, b=17.919(2) A, c=7.3580(10) A, beta=98.290(10) degrees, Z=4. In both molecules 1 and 3, two carbon atoms from aryl groups, two sulfur and two nitrogen atoms from thione ligands form a distorted octahedral geometry around tin(IV) with trans-C(2), cis-N(2), cis-S(2) configurations. Compound 5 C(45)H(39)NO(3)SSn(2) is monoclinic, space group P2(1)/n, a=9.1148(2) A, b=29.2819(6), c=15.5556(4) A, beta=106.2851(9) degrees, Z=4. Complex 5 contains two [(C(6)H(5))(3)Sn(IV)] moieties linked by a double deprotonated 2-mercaptonicotinic acid (H(2)mna). Both tin(IV) ions are five coordinated. This complex is the an example of a pentacoordinated Ph(3)SnXY system with an axial-equatorial arrangement of the phenyl groups at Sn(1) atom. Compounds 1, 3 and 5 were tested for in vitro cytotoxicity against the cancer cell line of sarcoma cells (mesenchymal tissue) from the Wistar rat, polycyclic aromatic hydrocarbons (benzo[a]pyrene) carcinogenesis. Compound 5 exhibits strong cytotoxic activity, while complexes 1 and 3 show less cytotoxic activity.     

A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy

The assembly of mitochondrial respiratory chain complex IV (cytochrome c oxidase) involves the coordinated action of several assembly chaperones. In Saccharomyces cerevisiae, at least 30 different assembly chaperones have been identified. To date, pathogenic mutations leading to a mitochondrial disorder have been identified in only seven of the corresponding human genes. One of the genes for which the relevance to human pathology is unknown is C2orf64, an ortholog of the S. cerevisiae gene PET191. This gene has previously been shown to be a complex IV assembly factor in yeast, although its exact role is still unknown. Previous research in a large cohort of complex IV deficient patients did not support an etiological role of C2orf64 in complex IV deficiency. In this report, a homozygous mutation in C2orf64 is described in two siblings affected by fatal neonatal cardiomyopathy. Pathogenicity of the mutation is supported by the results of a complementation experiment, showing that complex IV activity can be fully restored by retroviral transduction of wild-type C2orf64 in patient-derived fibroblasts. Detailed analysis of complex IV assembly intermediates in patient fibroblasts by 2D-BN PAGE revealed the accumulation of a small assembly intermediate containing subunit COX1 but not the COX2, COX4, or COX5b subunits, indicating that C2orf64 is involved in an early step of the complex IV assembly process. The results of this study demonstrate that C2orf64 is essential for human complex IV assembly and that C2orf64 mutational analysis should be considered for complex IV deficient patients, in particular those with hypertrophic cardiomyopathy.     

Synthesis, X-ray structure, and anti-leukemic activity of oxovanadium(IV) complexes

In a systematic effort to identify and develop effective anticancer agents, four oxovanadium(IV) complexes with 1,10-phenanthroline (Phen) or 4,7-dimethyl-1,10-phenanthroline (Me2-Phen) as ligand(s) were synthesized and characterized. Among the four oxovanadium(IV) complexes synthesized, the crystal structure of the bis(phenanthroline)oxovanadium(IV) complex bis(1,10-phenanthroline)sulfatooxovanadium(IV) ([VO(SO4)(Phen)2], compound 1) has been determined. Compound 1 crystallized in the space group P2(1)/n with unit cell parameters a = 14.2125(17) A, b = 10.8628(13) A, c = 20.143(2) A, alpha = 90 degrees, beta = 102.569(2) degrees, gamma = 90 degrees, V = 3035.3(6) A3, and Z = 4. The refinement of compound 1 by full-matrix least-squares techniques gave an R factor of 0.0785 for 4356 independent reflections. The structure contains two enantiomorphous molecules, lambda and delta, which are related by an inversion center. Compound 1 exhibited 3.5-fold more potent cytotoxic activity against NALM-6 human leukemia cells than the mono(phenanthroline)oxovanadium(IV) complex (diaqua)(1,10-phenanthroline)sulfatooxovanadium(IV) ([VO(SO4)(Phen)(H2O)2], compound 2) (IC50 values: 0.97+/-0.10 microM versus 3.40+/-0.20 microM: P=0.0004). Methyl substitution in the phenanthroline ligand enhanced the anti-leukemic activity of the mono(phenanthroline)oxovanadium(IV) complex 4.4-fold (IC50 values: 0.78+/-0.10 microM, compound 4, versus 3.40+/-0.20 microM, compound 2; P=0.0003) and the anti-leukemic activity of the bis(phenanthroline)oxovanadium(IV) complex 5.7-fold (IC50 values: 0.17+/-0.02 microM, compound 3, versus 0.97+/-0.10 microM, compound 1; P=0.001). The leading oxovanadium compound, bis(4,7-dimethyl-1,10-phenanthroline)sulfatooxovanadium(IV) ([VO(SO4)(Me2-Phen)2], compound 3) triggered the production of reactive oxygen species (ROS) in human leukemia cells, caused G1-arrest and inhibited clonogenic growth at nanomolar concentrations.     

Vanadyl-induced Fenton-like reaction in RNA. An ESR and spin trapping study.

Vanadyl (VO2+) complexed to RNA reacts with hydrogen peroxide in a Fenton-like manner producing hydroxyl radicals (.OH). The hydroxyl radicals can be spin trapped with 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) forming the DMPO-OH spin adduct. In addition, in the presence of ethanol the formation of the hydroxyethyl radical adduct of DMPO (DMPO-ETOH) confirms the production of hydroxyl radicals by the RNA/VO2+ complex. When the reaction between the RNA/VO2+ complex and H2O2 is carried out in the presence of the spin trap 2-methyl-2-nitrosopropane (MNP), radicals produced in the reaction of .OH with RNA are trapped. Base hydrolysis of the MNP-RNA adducts (pH 12) followed by a reduction in the pH to pH 7 after hydrolysis is complete, yields an MNP adduct with a well-resolved ESR spectrum identical to the ESR spectrum obtained from analogous experiments with poly U. The ESR spectrum consists of a triplet of sextets (aN = 1.48 mT, a beta N = 0.25 mT and a beta H = 0.14 mT), indicating that the unpaired nitroxide electron interacts with the nuclei of a beta-nitrogen and beta-hydrogen. The results suggest that the .OH generated in the RNA/VO2+ reaction with H2O2 add to the C(5) carbon of uracil forming a C(6) carbon centered radical. This radical is subsequently spin trapped by MNP.     

Spectrophotometric and ESR evidence for vanadium(IV) deferoxamine complexes.

Complexes of vanadium(IV), vanadyl, are reported to be formed with the trihydroxamic acid deferoxamine (H3DF+). One complex exhibits a reddish-violet color, with a major absorbance peak at 386 nm and a smaller peak at 520 nm. This complex is potentially useful for the microdetermination of vanadyl. The apparent molar absorptivity is 3.91 mM-1 cm-1, and the complex obeys Beer's law in the concentration range of 0.6-63 ppm. Electron spin resonance studies indicate the formation of two vanadyl complexes that are 1:1 in vanadyl and deferoxamine, but have two or three bound hydroxamate groups. ESR and spectrophotometric evidence indicate that the red, low pH form, involves an octahedral vanadium (4+) ion coordinated by three hydroxamate ligands. One of these hydroxamates is displaced by an oxygen at pH greater than 2.8 according to the following equilibria: VO2+ + H3DF+ in equilibrium with VIV(DF)2+ + H3O+, VIV(DF)2+ + H2O in equilibrium with VO(HDF)+ + H+, where pk2 = 2.8.     

Speciation of phytate ion in aqueous solution. Dimethyltin(IV) interactions in NaCl(aq) at different ionic strengths

As the introduction of a systematic study on the sequestering ability of phytate (Phy) towards heavy metal and organometal cations, this paper describes the results of an investigation (at t=25 degrees C by potentiometry, ISE-H(+) glass electrode) of its interactions with dimethyltin(IV) cation [(CH(3))(2)Sn(2+), DMT] in NaCl aqueous solutions at different ionic strengths (0.1< or =I (mol L(-1))< or =1), in the pH range 2.5< or =pH< or =8.5 and considering metal to ligand ratios 1:1< or =DMT:Phy< or =4:1. We observed the formation of 18 DMT(i)H(j)Phy((12-2i-j)-) species: with i=1 and 0< or =j< or =7; i=2 and 0< or =j< or =5; i=3 and 0< or =j< or =3. Their complex formation constant values are fairly dependent on ionic strength and this dependence was modeled by a Debye-Hückel type equation. The speciation of phytic acid and dimethyltin(IV) is also dependent on the metal to ligand ratio; the dependence of the stability of phytate-dimethyltin(IV) species on both the phytate protonation step and the number of cations bound to the ligand has been modeled and an empirical predictive relationship is also proposed. From the results obtained it emerged that phytate has very good sequestering ability towards (CH(3))(2)Sn(2+). Comparisons are made with other ligands, such as ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA) and phosphate.     

Mechanisms of peroxynitrite decomposition catalyzed by FeTMPS, a bioactive sulfonated iron porphyrin

Peroxynitrite is a known cytotoxic agent that plays a role in many pathological conditions. Various peroxynitrite decomposition catalysts and pathways are being explored to develop efficient therapeutic agents that can safely remove peroxynitrite from cells and tissues. Water-soluble porphyrins, such as iron(III) meso-tetra(2,4,6-trimethyl-3,5-disulfonato)porphine chloride (FeTMPS) and iron(III) meso-tetra(N-methyl4-pyridyl)porphine chloride (FeTMPyP), have been shown to react catalytically with peroxynitrite (ONOO-). However, their mechanisms are yet to be fully understood. In this study, we have explored the reactivity of FeTMPS in the catalytic decomposition of peroxynitrite. The mechanism of this complex process has been determined. According to this mechanism, Fe(III)TMPS is oxidized by peroxynitrite to produce oxoFe(lV)TMPS and NO2 (k1 = 1.3 x 10(5) M(-1)(s(-1). The porphyrin is then reduced back to Fe(III)TMPS by nitrite, but this rate (k2 = 1.4 x 10(4) M(-1)s(-1)) is not sufficient to maintain the catalytic process at the observed rate. The overall rate of peroxynitrite decomposition catalysis, kcat, was determined to be 6 x 10(4) M(-1)s(-1), under typical conditions. We have postulated that an additional reduction pathway must exist. Kinetic simulations showed that a reaction of oxoFe(IV)TMPS with NO2 (k3 = 1.7 x 10(7) M((-1)s(-1)) could explain the behavior of this system and account for the fast reduction of oxoFe(IV)TMPS to Fe(III). Using the kinetic simulation analysis, we have also shown that two other rearrangement reactions, involving FeTMPS and peroxynitrite, are plausible pathways for peroxynitrite decay. A "cage-return" reaction between the generated oxoFe(IV)TMPS and NO2 (k8 = 5.4 x 10(4) M(-1)s(-1)), affording Fe(III)TMPS and nitrate, and a reaction between oxoFe(IV)TMPS and peroxynitrite (k7 = 2.4 x 10(4) M(-1)s(-1)) that affords oxoFe(IV)TMPS and nitrate are presented. The mechanism of FeTMPS-catalyzed peroxynitrite decay differs markedly from that of FeTMPyP, providing some insight into the reactivity of metal centers with peroxynitrite and biologically important radicals such as NO2.     

The binuclear iron site of the membrane-bound methane hydroxylase from Methylococcus capsulatus (strain M)

The particulate membrane-bound methane hydroxylase (pMMOH) was isolated from methane-oxidizing cells of Methylococcus capsulatus (strain M). At SDS PAGE, pMMOH displays three bands: 47 (alpha), 27 (beta), and 25 kDa (gamma). The ESR spectrum of pMMOH incubated with hydrogen peroxide (final concentration 20 mM) at 4 degrees C exhibited, along with the copper signal of type I with g = 2.05, signals of cytochrome with g = 3.0 and of high-spin ferriheme with g = 6.00. After incubation at -30 degrees C, additional signals with g 8.5 and 13.5 were observed. These signals, which have not been recorded previously in pMMOH preparations, are due to an intermediate of the pMMOH active site, which arises in the reaction of hydrogen peroxide with pMMOH at -30 degrees C. It was established that this intermediate is a high-spin dimer [Fe(IlI)-Fe(IV)] with S = 9/2 and different degree of rhombic distortion of structure (it is responsible for both signals). Presumably, the signal with g = 8.5 also arises from the same dimer [Fe(III)-Fe(IV)], but with S = 7/2. The presence of the intermediate [Fe(lII)-Fe(IV)] in pMMOH preparations suggests that the original state of the pMMOH active site is the dimer [Fe(III)-Fe(III)] which is located in the beta-subunit and cannot be detected by ESR. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2008, vol. 34, no. 2; see also http:// www.maik.ru.