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At least 19 recordsLinked to original sources
PubMed1992

Effects of manganese forms on biogenic amines in the brain and behavioral alterations in the mouse: long-term oral administration of several manganese compounds.

This work has identified the relative toxicity of four forms of manganese, using biogenic amine levels, tissue retention, weight gain, and activity scores as criteria. Male mice were chronically treated with four forms of manganese administered orally, mixed with the diet, for 12 months. The food intake for the control mice and the mice exposed to manganese was similar, but the manganese treatment reduced normal weight gain in the mice. The Mn levels were higher in some parts of brain after feeding insoluble salts than after the soluble salts. The concentration of manganese was significantly increased in the liver and spleen of the manganese carbonate-exposed group, compared with the concentration in the control group. Manganese dioxide feeding lowered dopamine and increased homovanilic acid. Since manganese dioxide is a powerful oxidizing agent in organic chemistry, it possibly enhanced the oxidative metabolite of dopamine. Accumulation of manganese in the brain correlated with reduced hypothalamic dopamine levels in the manganese acetate-exposed group; and the amount of manganese accumulated correlated with the intensity of suppression of motor activity. These findings indicate that manganese dioxide is more toxic than divalent manganese. Of the divalent manganese compounds, manganese acetate seemed to have the greatest toxic effect.

Animals↗
PubMed1983

Effects of manganese compounds on carcinogenicity of nickel subsulfide in rats.

The effects of manganese compounds upon the carcinogenicity of alpha Ni3S2 were tested in male Fischer rats. In Experiment I, rats were given i.m. injections of alpha Ni3S2 (2.5 mg) and Mn dust (2.0 mg), singly or in combination. By 100 weeks, sarcomas occurred at the injection site in 0 of 24 rats in the vehicle control group, in 0 of 24 rats that received Mn dust alone, and in 23 of 24 rats that received alpha Ni3S2 alone. Combined administration of alpha Ni3S2 plus Mn dust as a single i.m. injection resulted in sarcomas in 14 of 23 rats (p less than 0.05 versus alpha Ni3S2 alone). In rats that received injections of alpha Ni3S2 in one thigh and Mn dust in the opposite thigh, the sarcoma incidence at the site of alpha Ni3S2 injection was 24 of 24 rats. In Experiment II, rats were given i.m. injections of alpha Ni3S2 (1.2 mg) and Mn compounds (MnS, Mn2O3, MnO2 or MN2(CO)10, in dosages equivalent to 1.0 mg of Mn), singly or in combination. No sarcomas occurred at the injection site in rats that received the vehicle or any of the manganese compounds alone. Sarcomas occurred in 13 of 27 rats that received alpha Ni3S2 alone; this sarcoma incidence was not reduced by admixture of any of the Mn compounds. The median tumor latent period and the median survival period were significantly longer (p less than 0.05) in rats that received MnS plus alpha Ni3S2, compared with rats that received alpha Ni3S2 alone, suggesting that MnS may have weak anticarcinogenic effect. These experiments demonstrate that inhibition of alpha Ni3S2-carcinogenesis by Mn dust is a local rather than a systemic effect, and that, with the possible exception of MnS, the other manganese compounds that were tested are ineffective as inhibitors of alpha Ni3S2-carcinogenesis.

Animals↗
PubMed1975

Dermal irritancy of metal compounds. Studies with palladium, platinum, lead, and manganese compounds.

Dermal irritancy of 14 materials, including several compounds of palladium, platinum and lead, and methylcyclopentadienyl manganese tricarbonyl, plus deionized water (negative control) and glacial acetic acid (positive control), was tested on male albino rabbits weighing 2 to 3 kg. Procedures and evaluation criteria were adopted from those in use by the National Institute for Occupational Safety and Health. Five materials were evaluated as unsafe for intact or abraded skin contact as judged by severity of responses: glacial acetic acid (C3H5PDCl)2, (NH4)2PdCl4, (NH4)2PdCl6, and PtCl4; one as safe for intact, but not for abraded, skin: K2PdCl6; and two as safe for intact skin but not for abraded skin unless protected: K2PdCl4 and PdCl2. The remainder were evaluated as safe for intact or abraded skin contact (irritancy grade less than 1 on a scale of 4): H2O, Pd(NH3)2Cl2, PdO, PtO2, PtCl2, PbCl2, PbO, MMT.

Acetates↗
PubMed1992

Oxidation of phenolic arylglycerol beta-aryl ether lignin model compounds by manganese peroxidase from Phanerochaete chrysosporium: oxidative cleavage of an alpha-carbonyl model compound.

Manganese peroxidase (MnP) oxidized 1-(3,5-dimethoxy-4-hydroxyphenyl)-2-(4-(hydroxymethyl)-2-methoxyphenoxy) -1,3-dihydroxypropane (I) in the presence of MnII and H2O2 to yield 1-(3,5-dimethoxy-4-hydroxyphenyl)- 2-(4-(hydroxymethyl)-2-methoxyphenoxy)-1-oxo-3-hydroxypropane (II), 2,6-dimethoxy-1,4-benzoquinone (III), 2,6-dimethoxy-1,4-dihydroxybenzene (IV), 2-(4-(hydroxymethyl)-2-methoxyphenoxy)-3-hydroxypropanal (V), syringaldehyde (VI), vanillyl alcohol (VII), and vanillin (VIII). MnP oxidized II to yield 2,6-dimethoxy-1,4-benzoquinone (III), 2,6-dimethoxy-1,4-dihydroxybenzene (IV), vanillyl alcohol (VII), vanillin (VIII), syringic acid (IX), and 2-(4-(hydroxymethyl)-2-methoxyphenoxy)-3-hydroxypropanoic acid (X). A chemically prepared MnIII-malonate complex catalyzed the same reactions. Oxidation of I and II in H2(18)O under argon resulted in incorporation of one atom of 18O into the quinone III and into the hydroquinone IV. Incorporation of one atom of oxygen from H2(18)O into syringic acid (IX) and the phenoxypropanoic acid X was also observed in the oxidation of II. These results are explained by mechanisms involving the initial one-electron oxidation of I or II by enzyme-generated MnIII to produce a phenoxy radical. This intermediate is further oxidized by MnIII to a cyclohexadienyl cation. Loss of a proton, followed by rearrangement of the quinone methide intermediate, yields the C alpha-oxo dimer II as the major product from substrate I. Alternatively, cyclohexadienyl cations are attacked by water. Subsequent alkyl-phenyl cleavage yields the hydroquinone IV and the phenoxypropanal V from I, and IV and the phenoxypropanoic acid X from II, respectively. The initial phenoxy radical also can undergo C alpha-C beta bond cleavage, yielding syringaldehyde (VI) and a C6-C2-ether radical from I and syringic acid (IX) and the same C6-C2-ether radical from II. The C6-C2-ether radical is scavenged by O2 or further oxidized by MnIII, subsequently leading to release of vanillyl alcohol (VII). VII and IV are oxidized to vanillin (VIII) and the quinone III, respectively.

Basidiomycota↗
PubMed1993

Subcellular and gel chromatographic distribution of manganese in the mouse brain: relation to the chemical form of chronically-ingested manganese.

The subcellular distribution of manganese and the binding characteristics of manganese to protein in the mouse brain were examined on G-75 Sephadex gel columns. Four manganese compounds were included at 2 g/kg in each food eaten by ddY mice for 12 months. The cerebral cortex manganese concentrations in the virtually insoluble manganese compounds were significantly higher than those in the control group. The brain striatal subcellular distribution and gel chromatographic profiles of manganese were similar among the divalent manganese compounds. On the contrary, the behaviour of MnO2 was little different from the divalent manganese compounds. There was more manganese associated with fast-migrating ligands in the striatal cytosol of the manganese-exposed group than in the control groups.

Acetates↗
PubMed1994

Mechanism of manganese peroxidase compound II reduction. Effect of organic acid chelators and pH.

The effect of oxalate, malonate, lactate, and succinate chelators on the reduction of Phanerochaete chrysosporium manganese peroxidase compound II by MnII was investigated using stopped-flow techniques. All rate data were collected from single-turnover experiments under pseudo-first-order conditions. With oxalate, the reduction of compound II by MnII exhibited saturation behavior when the observed pseudo-first-order rate constants were plotted against oxalate concentration. The plots passed through the origin, indicating that the reduction by MnII is irreversible at all concentrations of oxalate. Maximal stimulation of the rate of compound II reduction occurred at 2 mM oxalate, the concentration of oxalate found in the extracellular medium of agitated cultures of this fungus. In contrast, maximal stimulation of the reduction of compound II by MnII only was observed at high (> 20 mM) nonphysiological concentrations of malonate and lactate. Furthermore, at low concentrations of malonate and lactate, the reduction of compound II appeared to be reversible. These results suggest that at physiological concentrations oxalate chelates and stabilizes MnIII, enhancing its efficient removal from the enzyme. The rate constants for compound II reduction exhibited bell-shaped curves as a function of pH and had optima at pHs 5.0-5.4. In the presence of succinate, triphasic kinetics were observed for compound II reduction by MnII. In contrast to the reduction of compound II by MnII, various chelators had no observable effect on the formation of compound I. However, they did affect the steady-state oxidation of 2,6-dimethoxyphenol.

Basidiomycota↗
PubMed1987

Electron paramagnetic resonance and spectrophotometric studies of the peroxide compounds of manganese-substituted horseradish peroxidase, cytochrome-c peroxidase and manganese-porphyrin model complexes.

Peroxide compounds of manganese protoporphyrin IX and its complexes with apo-horseradish peroxidase and apocytochrome-c peroxidase were characterized by electronic absorption and electron paramagnetic resonance spectroscopies. An intermediate formed upon titration of Mn(III)-horseradish peroxidase with hydrogen peroxide exhibited a new electron paramagnetic resonance absorption at g = 5.23 with a definite six-lined 55Mn hyperfine (AMn = 8.2 mT). Neither a porphyrin pi-cation radical nor any other radical in the apoprotein moiety could be observed. The reduced form of Mn-horseradish peroxidase, Mn(II)-horseradish peroxidase, reacted with a stoichiometric amount of hydrogen peroxide to form a peroxide compound whose electronic absorption spectrum was identical with that formed from Mn(III)-horseradish peroxidase. The electronic state of the peroxide compound of manganese horseradish peroxidase was thus concluded to be Mn(IV), S = 3/2. Mn(III)-cytochrome-c peroxidase reacted with stoichiometry quantities of hydrogen peroxide to form a catalytically active intermediate. The electronic absorption spectrum was very similar to that of a higher oxidation state of manganese porphyrin, Mn(V). Since the peroxide compound of manganese cytochrome-c peroxidase retained two oxidizing equivalents per mol of the enzyme (Yonetani, T. and Asakura, T. (1969) J. Biol. Chem. 244, 4580-4588), this peroxide compound might contain an Mn(V) center.

Cytochrome-c Peroxidase↗
PubMed1989

Thiol-mediated oxidation of nonphenolic lignin model compounds by manganese peroxidase of Phanerochaete chrysosporium.

In the presence of MnII, H2O2, and glutathione (GSH), manganese peroxidase oxidized veratryl alcohol (I) to veratraldehyde (IV). Anisyl alcohol (II) and benzyl alcohol (III) were also oxidized by this system to their corresponding aldehydes (V and VI). In the presence of GSH, chemically prepared MnIII or gamma-irradiation also catalyzed the oxidation of I, II, and III to IV, V, and VI, respectively. GSH and dithiothreitol rapidly reduced MnIII to MnII in the absence of aromatic substrates and the dithiothreitol was oxidized to its disulfide (4,5-dihydroxyl-1,2-dithiane). These results indicate that the thiol is oxidized by enzyme-generated MnIII to a thiyl radical. The latter abstracts a hydrogen from the substrate, forming a benzylic radical which reacts with another thiyl radical to yield an intermediate which decomposes to the benzaldehyde product. In the presence of MnII, GSH, and H2O2, manganese peroxidase also oxidized 1-(4-ethoxy-3-methoxy-phenyl)-2-(4'-hydroxymethyl-2'-methoxyphenoxy)- 1,3-dihydroxypropane (XII) to yield vanillyl alcohol (VII), vanillin (VIII), 1-(4-ethoxy-3-methoxyphenyl)-1,3-dihydroxypropane (XVI), 1-(4-ethoxy-3-methoxyphenyl)-1-oxo-3-hydroxypropane (XIX), and several C alpha oxidized dimeric products. Abstraction of the C alpha (A ring) hydrogen of the dimer (XII) yields a benzylic radical, leading to C beta oxygen ether cleavage. The resultant intermediates yield the ketone (XIX) and vanillyl alcohol (VII) or vanillin (VIII). Alternatively, benzylic radical formation at the C' alpha position (B ring) leads to radical cleavage, yielding a quinone methide and a C beta radical, which yield vanillin and the 1,3-diol (XVI), respectively. In these reactions, MnIII oxidizes a thiol to a thiyl radical which subsequently abstracts a hydrogen from the substrate to form a benzylic radical. The latter undergoes nonenzymatic reactions to yield the final products.

Aerobiosis↗
PubMed1990

The S3 state of photosystem II: differences between the structure of the manganese complex in the S2 and S3 states determined by X-ray absorption spectroscopy.

O2-evolving photosystem II (PSII) membranes from spinach have been cryogenically stabilized in the S3 state of the oxygen-evolving complex. The cryogenic trapping of the S3 state was achieved using a double-turnover illumination of dark-adapted PSII preparations maintained at 240 K. A double turnover of PSII was accomplished using the high-potential acceptor, Q400, which is the high-spin iron of the iron-quinone acceptor complex. EPR spectroscopy was the principal tool establishing the S-state composition and defining the electron-transfer events associated with a double turnover of PSII. The inflection point energy of the Mn X-ray absorption K-edge of PSII preparations poised in the S3 state is the same as for those poised in the S2 state. This is surprising in light of the loss of the multiline EPR signal upon advancing to the S3 state. This indicates that the oxidative equivalent stored within the oxygen-evolving complex (OEC) during this transition resides on another intermediate donor which must be very close to the manganese complex. An analysis of the Mn extended X-ray absorption fine structure (EXAFS) of PSII preparations poised in the S2 and S3 states indicates that a small structural rearrangement occurs during this photoinduced transition. A detailed comparison of the Mn EXAFS of these two S states with the EXAFS of four multinuclear mu-oxo-bridged manganese compounds indicates that the photosynthetic manganese site most probably consists of a pair of binuclear di-mu-oxo-bridged manganese structures. However, we cannot rule out, on the basis of the EXAFS analysis alone, a complex containing a mononuclear center and a linear trinuclear complex. The subtle differences observed between the S states are best explained by an increase in the spread of Mn-Mn distances occurring during the S2----S3 state transition. This increased disorder in the manganese distances suggests the presence of two inequivalent di-mu-oxo-bridged binuclear structures in the S3 state.

Benzoquinones↗