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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A new iron-sulfur protein, distinct from the soluble chloroplast ferredoxin, was isolated from chloroplast membranes. The isolated protein, purified to homogeneity, had a molecular weight of about 8000 and 4 atoms of iron and 4 inorganic sulfides per mole. Its absorption spectrum had a broad absorbance band in the 400 nm region, a shoulder at approximately 310 nm, and a peak around 280 nm. The absorbance ratio A(400) to A(280) was 0.55. The electron paramagnetic resonance spectrum (measured at 12 degrees K) of the reduced protein was similar to that of other reduced iron-sulfur proteins, showing a major resonance line at g = 1.94. The isolated protein, when photoreduced by spinach chloroplasts, can in turn transfer electrons to mammalian cytochrome c. However, the photoreduced protein cannot replace soluble ferredoxin in NADP(+) reduction because of its apparent inability to interact with the chloroplast enzyme, ferredoxin-NADP(+) reductase. The relation of the isolated iron-sulfur protein to the bound ferredoxin that acts as the primary electron acceptor in Photosystem I is discussed.
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PMID:The isolation and characterization of a new iron-sulfur protein from photosynthetic membranes. 436 63

A thermostable beta-galactosidase (EC 3.2.1.23; beta-dgalactoside galactohydrolase) was found to be inducible in an extreme thermophile resembling Thermus aquaticus. Enzyme induction was achieved by the addition of lactose, galactose, or the alpha-galactoside, melibiose, to growing cultures. The addition of glucose to induced cultures had a repressive effect on further enzyme synthesis. The enzyme was purified 78-fold, and the optimum temperature and pH for activity were determined to be 80 C and pH 5.0, respectively. The enzyme was activated by both manganese and ferrous iron. Sulfhydryl activation and thermal stabilization indicate that the thermophilic beta-galactosidase is a sulfhydryl enzyme. Kinetic determinations at 80 C established a K(m) of 2.0 x 10(-3)m for the chromogenic substrate o-nitrophenyl beta-d-galactopyranoside (ONPG) and a K(1) of 7.5 x 10(-3)m for lactose. The Arrhenius energy of activation (for the hydrolysis of ONPG) was calculated to be 13.7 kcal/mole. A molecular weight of 5.7 x 10(5) daltons was estimated by elution of the enzyme from Sephadex 4B.
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PMID:Induction and characterization of -galactosidase in an extreme thermophile. 502 73

Ferredoxin from Bacillus polymyxa contains (per mole) four non-heme iron residues, four acid-labile sulfide residues, and four cysteine residues. Its molecular weight is approximately 8,800, and it has an oxidation-reduction potential (E(m)) of -390 mv. It is active as an electron carrier in several ferredoxin-linked enzyme systems.
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PMID:Four-iron (sulfide) ferredoxin from Bacillus polymyxa. 503 Jun 19

The soluble hydrogenase of Desulfovibrio vulgaris was purified and some of its properties are described. The molecular weight was determined for the enzyme by sedimentation equilibrium (45,400) and amino acid analysis (44,800). The hydrogenase appears to be a loosely coiled molecule or to have a high axial ratio, which is reflected in an unusually low sedimentation coefficient (2.58S) and a low diffusion coefficient (D 5.85). The molecular weight of the hydrogenase (41,000), as calculated by the Svedberg equation, was in general agreement with the sedimentation equilibrium molecular weight. Amino acid analysis revealed the presence of six halfcystine residues per mole of enzyme and a total of 417 amino acid residues. The specificity of the hydrogenase and its capacity to reduce certain low potential dyes and cytochrome c(3) was studied. Metal analysis of the hydrogenase indicated the presence of 1 mole of ferrous iron per mole of enzyme.
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PMID:Purification and properties of a hydrogenase from Desulfovibrio vulgaris. 554 Oct 10

A colorimetric assay was developed for studying the kinetics of iron oxidation with whole cells of the chemoautotroph, Ferrobacillus ferrooxidans. The assay was more advantageous than the conventional method of Warburg manometry because of its simplicity, rapidity, and the small amount of cells required. The assay measured Fe(3+) as a chloride complex which absorbs at 410 nm. Kinetic analysis showed the apparent K(m) for iron oxidation to be 5.4 x 10(-3)m in an unbuffered system and 2.2 x 10(-3)m in the presence of beta-alanine-SO(4) (2-) buffer. Glycine and beta-alanine buffers were used in the measurement of the pH optimum for iron oxidation; the optimum ranged from 2.5 to 3.8. The effect of pH was primarily on the V(max) while the K(m) remained constant. Added SO(4) (2-) was found to stimulate iron oxidation by increasing the V(max) of iron oxidation by whole cells, but it did not affect the K(m). Results of assays of iron oxidation in systems containing various mole percentages of SO(4) (2-) and Cl(-) indicated that Cl(-) did not inhibit iron oxidation but that SO(4) (2-) was required. Sulfate could be partially replaced by HPO(4) (2-) and HAsO(4) (2-) but not by BO(3) (-), MoO(4) (2-), NO(3) (-), or Cl(-); formate and MoO(4) (2-) inhibited iron oxidation.
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PMID:Kinetic studies of iron oxidation by whole cells of Ferrobacillus ferrooxidans. 580 80

A hydrogenase from a new species of sulfate reducing bacterium has been isolated and characterized. In contrast to other hydrogenases isolated from Desulfovibrio, this enzyme is found in the cytoplasmic fraction rather than in the periplasm. The specific activity of the enzyme, as measured in the hydrogen evolution assay, is twice as high as the specific activity of the hydrogenase from D. gigas. It also differentiates itself from the periplasmic Desulfovibrio hydrogenases by being more active in the hydrogen evolution rather than in the hydrogen uptake assay. The enzyme was shown to contain 0.9 atoms of nickel, 11 atoms of iron and 10 atoms of labile sulfide per mole of enzyme. It exhibits an unusually low intensity of the g = 2.31 nickel EPR signal in the isolated enzyme but shows a normal intensity for the g = 2.19 nickel EPR signal when reduced under hydrogen.
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PMID:A cytoplasmic nickel-iron hydrogenase with high specific activity from Desulfovibrio multispirans sp. N., a new species of sulfate reducing bacterium. 609 50

The number of iron atoms in the dimeric iron-containing superoxide dismutase from Pseudomonas ovalis and their atomic positions have been determined directly from anomalous scattering measurements on crystals of the native enzyme. To resolve the long-standing question of the total amount of iron per molecule for this class of dismutase, the occupancy of each site was refined against the measured Bijvoet differences. The enzyme is a symmetrical dimer with one iron site in each subunit. The iron position is 9 A from the intersubunit interface. The total iron content of the dimer is 1.2 +/- 0.2 moles per mole of protein. This is divided between the subunits in the ratio 0.65:0.55; the difference between them is probably not significant. Since each subunit contains, on average, slightly more than half an iron atom we conclude that the normal state of this enzyme is two iron atoms per dimer but that some of the metal is lost during purification of the protein. Although the crystals are obviously a mixture of holo- and apo-enzymes, the 2.9 A electron density map is uniformly clean, even at the iron site. We conclude that the three-dimensional structures of the iron-bound enzyme and the apo-enzyme are identical.
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PMID:The iron content of iron superoxide dismutase: determination by anomalous scattering. 613 8

The effect of aliphatic thiols, including glutathione, cysteine, and dithiothreitol, on the anaerobic reduction of Cu(II)-bleomycin was examined. At neutral pH, cysteine is more efficient in reducing Cu(II)-bleomycin than either dithiothreitol or glutathione, while at alkaline pH the rate of reduction with all three reagents increases substantially. A kinetic treatment suggests that 2 equiv of thiol is required for each mole of Cu(II)-bleomycin reduced. Material balance studies verify this stoichiometry. If anaerobic reduction of Cu(II)-bleomycin is carried out in the presence of Fe(II), iron is chelated by the drug. This metal-drug complex is capable of degrading DNA when O2 is introduced. The extent of DNA degradation, as measured by the release of malondialdehyde-like chromogens from the DNA, is directly dependent on the amount of Cu(II)-bleomycin reduced.
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PMID:Reduction of copper(II)-bleomycin: a model for in vivo drug activity. 617 33

One molecular form of cytochrome P-450IIA from liver microsomes of guinea pigs treated with 3-methylcholanthrene was purified to a specific content of 17.4 nmoles/mg of protein. The difference spectrum of reduced hemoprotein-carbon monoxide complex of this cytochrome exhibits an absorption maximum at 448 nm. The absolute absorption spectrum of the oxidized form of this hemoprotein suggests a high-spin state of heme iron. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis of the purified protein shows a single band of polypeptide stained with Coomassie brilliant blue at the position corresponding to Mr 54,000. On the other hand, the other two forms of cytochrome P-450, cytochrome P-450I and P-450IIB, were also separated and purified to specific contents of 8.7 and 5.2 nmoles/mg of protein, respectively. Both cytochrome P-450I and P-450IIB exhibit absorption maxima at 450 nm in the difference spectrum of reduced hemoprotein-carbon monoxide complex, and a low-spin state of ferric iron in the heme. The spectrophotometrical property of cytochrome P-450I and P-450IIB was clearly different from that of cytochrome P-450IIA. Molecular activities of a reconstituted aryl hydrocarbon hydroxylase (EC 1.14.14.1) containing, respectively, cytochrome P-450I, P-450IIA, and P-450IIB were 0.224, 0.250, and 0.395 (moles per minute per mole of cytochrome P-450), and were estimated to be one-tenth that of cytochrome P-448 induced in rat liver by 3-methylcholanthrene, indicating the presence of the low inducibility by 3-methylcholanthrene of aryl hydrocarbon hydroxylase in liver microsomes of guinea pigs.
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PMID:Purification and characterization of three forms of microsomal cytochrome P-450 in liver from 3-methylcholanthrene-treated guinea pigs. 630 24

Periodate treatments of apo human serum transferrin (HST), and apo chicken ovotransferrin (COT) were previously reported to cause a rapid loss of Fe+3 binding capacity, with a loss of 3 to 5 tyrosine residues [P. AZARI AND J. L. PHILLIPS (1970) Arch. Biochem. Biophys. 138, 32-38; K. F. GEOGHEGAN, J. L. DALLAS, AND R. E. FEENEY (1980) J. Biol. Chem. 255, 11429-11434]. The effects of periodate and hydrogen peroxide on human lactotransferrin (HLT), HST, and COT have been compared. All three apotransferrins were rapidly inactivated and lost approximately 4 to 5 tyrosine residues by 5 mM periodate treatment; their iron complexes had little or no inactivation and losses of approximately 1 to 2 tyrosine residues. All three iron transferrins were highly resistant to inactivation by 5 mM periodate in bicarbonate, with or without the addition of phosphate, while in phosphate (with ambient carbonate) Fe2HLT was highly resistant, Fe2COT slightly less resistant, and Fe2HST much less resistant. Similar oxidations of methionines to the sulfoxides were found in both the apo and iron forms. After 150 min of 5 mM periodate treatment HST lost approximately 3 (apo 3.1, iron 2.8) of 9, HLT approximately 3 (apo 2.6, iron 2.9) of 6, and COT approximately 7 (apo 7.2, iron 7.2) of 11 methionines per mole of protein. In the presence of 8 M urea HST had essentially all of its methionine residues oxidized by periodate, but only lost part of its activity on renaturation. Treatment of all apo transferrins with 300 mM hydrogen peroxide resulted in little or no losses (less than 10%) in activity. HST lost approximately one-third of its methionines and no tyrosines during the 300 mM hydrogen peroxide treatment. Therefore the essentiality of tyrosines for all three transferrins was confirmed and the nonessentiality of methionines was demonstrated.
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PMID:Comparative oxidations of tyrosines and methionines in transferrins: human serum transferrin, human lactotransferrin, and chicken ovotransferrin. 631 90


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