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

Production of rat transferrin containing a single hybrid glycan was induced by treating rats with swainsonine, an inhibitor of alpha-mannosidase II. The principal component of this variant transferrin containing one sialic acid residue per mole of protein was separated from other forms of transferrin by anion-exchange chromatography, followed by lectin affinity chromatography. Transferrin bearing the hybrid glycan was degraded in vivo with a half-life of 14 h as compared with 40 h for transferrin containing a standard diantennary glycan. By using 125I-labelled tyramine-cellobiose, a label whose discharge from lysosomes is strongly retarded, organs rich in reticuloendothelial elements (liver, bone marrow, lungs, and spleen) were identified as the major sites of catabolism of the transferrin variant. The liver took up more 59Fe from the variant (26% of the dose in 90 min) than from control rat transferrin (12%). The excess iron uptake was reduced by the intravenous injection of either human transferrin or ovalbumin, and it was abolished by administering both. Macrophages from bone marrow and lungs degraded the transferrin variant in vitro. The degradation was significantly enhanced when transferrin receptors were blocked by human transferrin, and it was significantly reduced by ovalbumin and methyl glucopyranoside.
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PMID:In vivo behaviour of rat transferrin bearing a hybrid glycan and its interaction with macrophages. 147 2

Microsomal P450s catalyze the monooxygenation of a large variety of hydrophobic compounds, including drugs, steroids, carcinogens, and fatty acids. The interaction of microsomal P450s with their electron transfer partner, NADPH-P450 reductase, during the transfer of electrons from NADPH to P450, for oxygen activation, may be important in regulating this enzyme system. Highly purified Bacillus megaterium P450BM-3 is catalytically self-sufficient and contains both the reductase and P450 domains on a single polypeptide chain of approximately 120,000 Da. The two domains of P450BM-3 appear to be analogous in their function and homologous in their sequence to the microsomal P450 system components. FAD, FMN, and heme residues are present in equimolar amounts in purified P450BM-3 and, therefore, this protein could potentially accept five electron equivalents per mole of enzyme during a reductive titration. The titration of P450BM-3 with sodium dithionite under a carbon monoxide atmosphere was complete with the addition of the expected five electron equivalents. The intermediate spectra indicate that the heme iron is reduced first, followed by the flavin residues. Titration of the protein with the physiological reductant, NADPH, also required approximately five electron equivalents when the reaction was performed under an atmosphere of carbon monoxide. Under an atmosphere of argon and in the absence of carbon monoxide, one of the flavin groups was reduced prior to the reduction of the heme group. The titration behavior of P450BM-3 with NADPH was surprising because no spectral changes characteristic of flavin semiquinone intermediates were observed. The results of the titration with NADPH can only be explained if (a) there was "rapid" intermolecular electron transfer between P450BM-3 molecules, (b) there is no kinetic barrier to the reduction of P450 by the one-electron-reduced form of the reductase, and (c) the "air-stable semiquinone" form of the reductase does not accumulate in this complex multidomain enzyme.
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PMID:P450BM-3: reduction by NADPH and sodium dithionite. 156 20

Toluene degradation occurred concomitantly with sulfate reduction in anaerobic microcosms inoculated with contaminated subsurface soil from an aviation fuel storage facility near the Patuxent River (Md.). Similar results were obtained for enrichment cultures in which toluene was the sole carbon source. Several lines of evidence suggest that toluene degradation was directly coupled to sulfate reduction in Patuxent River microcosms and enrichment cultures: (i) the two processes were synchronous and highly correlated, (ii) the observed stoichiometric ratios of moles of sulfate consumed per mole of toluene consumed were consistent with the theoretical ratio for the oxidation of toluene to CO2 coupled with the reduction of sulfate to hydrogen sulfide, and (iii) toluene degradation ceased when sulfate was depleted, and conversely, sulfate reduction ceased when toluene was depleted. Mineralization of toluene was confirmed in experiments with [ring-U-14C]toluene. The addition of millimolar concentrations of amorphous Fe(OH)3 to Patuxent River microcosms and enrichment cultures either greatly facilitated the onset of toluene degradation or accelerated the rate once degradation had begun. In iron-amended microcosms and enrichment cultures, ferric iron reduction proceeded concurrently with toluene degradation and sulfate reduction. Stoichiometric data and other observations indicate that ferric iron reduction was not directly coupled to toluene oxidation but was a secondary, presumably abiotic, reaction between ferric iron and biogenic hydrogen sulfide.
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PMID:Microbial degradation of toluene under sulfate-reducing conditions and the influence of iron on the process. 157 81

In order to select the method of water regeneration from air moisture condensate in a manned enclosed environment, the procedure of water decontamination from ethylene glycol was investigated. The process developed at t 20-22 degrees C and the following concentrations of C2H6O2 = 0.0125-0.5 mole/l, H2O2 = 1-5 mole/l, and catalyst = 1.7-50% wt. In the presence of 6.67 g/l of homogeneous catalyst FeSO4.7H2O, destructive oxidation of ethylene glycol to yield CO2 in the system 0.1 M C2H6O2 + 1M H2O2 proceeded effectively. However, the iron concentration in the decontaminated water exceeded significantly the maximally allowable concentration of iron in potable water as well as in industrial and non-industrial sewage. Heterogeneous MnO- and PbO-based catalysts provided no more than 20% ethylene glycol oxidation. Siderite, a natural mineral containing 33% wt. Fe2+, proved a more effective catalyst of ethylene glycol oxidation. When ethylene glycol and hydrogen peroxide were used at ratios of 1:30 and 1:80 with 5% wt. siderite, the degree of C2H6O2 to CO2 conversion was 99.2% and 99.8, respectively.
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PMID:[Water purification from ethylene glycol by catalytic oxidation using hydrogen peroxide]. 168 10

Histochemical determinations of copper, zinc, and iron in intradermal pigmented nevi and melanomas revealed the presence of copper and iron in melanoma but not in nevi. Zinc was not detected in either melanomas or nevi. However, melanin was removed from the tissues prior to staining; therefore, it is possible that zinc was also removed by the procedure. Although the function of copper and iron in the melanoma cell is not known, they may be components of abnormal enzymes.
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PMID:Histochemical determinations of copper, zinc, and iron in pigmented nevi and melanoma. 151 Feb 28

Dihydroorotate dehydrogenase (DHODase) has been purified 400-fold from the rodent malaria parasite Plasmodium berghei to apparent homogeneity by Triton X-100 solubilization followed by anion-exchange, Cibacron Blue F3GA-agarose affinity, and gel filtration chromatography. The purified enzyme has a molecular mass of 52 +/- 2 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and of 55 +/- 6 kDa by gel filtration chromatography, and it has a pI of 8.2. It is active in monomeric form, contains 2.022 mol of iron and 1.602 acid-labile sulfurs per mole of enzyme, and does not contain a flavin cofactor. The purified DHODase exhibits optimal activity at pH 8.0 in the presence of the ubiquinone coenzyme CoQ6, CoQ7, CoQ9, or CoQ10. The Km values for L-DHO and CoQ6 are 7.9 +/- 2.5 microM and 21.6 +/- 5.5 microM, respectively. The kcat values for both substrates are 11.44 min-1 and 11.70 min-1, respectively. The reaction product orotate and an orotate analogue, 5-fluoroorotate, are competitive inhibitors of the enzyme-catalyzed reaction with Ki values of 30.5 microM and 34.9 microM, respectively. The requirement of the long-chain ubiquinones for activity supports the hypothesis of the linkage of pyrimidine biosynthesis to the electron transport system and oxygen utilization in malaria by DHODase via ubiquinones [Gutteridge, W. E., Dave, D., & Richards, W. H. G. (1979) Biochim. Biophys. Acta 582, 390-401].
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PMID:Purification and characterization of dihydroorotate dehydrogenase from the rodent malaria parasite Plasmodium berghei. 184 78

Mn-superoxide dismutase (SOD) and Fe-SOD were isolated from Methylomonas J, an aerobic methylotrophic bacterium, grown in methylamine media containing either manganese (Mn-rich medium) or iron (Fe-rich medium), respectively. The specific activity of the Mn-SOD was 2250 units mg-1 (mol of Mn)-1 (mol of dimer)-1, and the metal content of the enzyme was 0.98 mol of Mn and 0.12 mol of Fe per mole of dimer, while those of Fe-SOD were 88.5 units mg-1 (mol of Fe)-1 (mol of dimer)-1 and 1.04 mol of Fe and 0.02 mol of Mn. The electrophoretic mobilities in the presence of sodium dodecyl sulfate, with or without urea, and the chromatographic behavior on an HPLC column using an octadodecyl silicated column and a gel permeation column were identical. Amino acid compositions were practically indistinguishable in both SODs. The enzyme activity was restored by dialysis of an apoprotein obtained from the Mn-enzyme with either manganese sulfate or ferrous ammonium sulfate up to an activity level similar to that for the native Mn-SOD and the native Fe-SOD, respectively. The same result has been reported with the reconstitution using an apoprotein obtained from the Fe-enzyme [Yamakura, F., Matsumoto, T., & Terauchi, K. (1990) Free Radical Res. Commun. (in press)]. These results suggest the possibility that both types of SODs are composed of a single apoprotein synthesized in cells grown in either the Fe-rich medium or the Mn-rich medium.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Iron- and manganese-containing superoxide dismutases from Methylomonas J: identity of the protein moiety and amino acid sequence. 184 99

Solvent kinetic isotope effect studies of electron transfer within xanthine oxidase have been performed, using a stopped-flow pH-jump technique to perturb the distribution of reducing equivalents within partially reduced enzyme and follow the kinetics of reequilibration spectrophotometrically. It is found that the rate constant for electron transfer between the flavin and one of the iron-sulfur centers of the enzyme observed when the pH is jumped from 10 to 6 decreases from 173 to 25 s-1 on going from H2O to D2O, giving an observed solvent kinetic isotope effect of 6.9. An effect of comparable magnitude is observed for the pH jump in the opposite direction, the rate constant decreasing from 395 to 56 s-1. The solvent kinetic isotope effect on kobs is found to be directly proportional to the mole fraction of D2O in the reaction mix for the pH jump in each direction, consistent with the effect arising from a single exchangeable proton. Calculations of the microscopic rate constants for electron transfer between the flavin and the iron-sulfur center indicate that the intrinsic solvent kinetic isotope effect for electron transfer from the neutral flavin semiquinone to the iron-sulfur center designated Fe/S I is substantially greater than for electron transfer in the opposite direction and that the observed solvent kinetic isotope effect is a weighted averaged of the intrinsic isotope effects for the forward and reverse microscopic electron-transfer steps.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Electron transfer within xanthine oxidase: a solvent kinetic isotope effect study. 188 20

A latent form of 'Ferrooxidase' exhibiting ferrocyanide-dependent O2 uptake was detected in the isolated spinach chloroplasts. Presence of a cationic detergent hexadecyl trimethyl ammonium bromide (CTAB) in the medium was essential to induce this activity. The association of this enzyme activity with photosystem II (PSII) particles as well as the ability of PSII particles to show oxidation of H2O2 (catalase like activity) indicated its possible relationship with water oxidation system. The protein catalysing this activity was purified to homogeneity and its molecular mass was found to be 34 kDa. The purified protein showed a complete dependence on an electron acceptor, namely ferricyanide, for the oxidation of H2O2. While with ferrocyanide in the presence of CTAB, the protein exhibits the ferrooxidase activity. For both activities, a sharp pH optima at 6.1 was observed. The km for H2O2 was 12.2 mM. The purified enzyme protein contained 4 atoms of calcium and 2 atoms of iron per mole of the enzyme. Unlike catalase, the enzyme reaction was insensitive to sodium azide even at 500 microM concentration. The enzyme was found to be sensitive to metal chelators like ethylene-glycol-bis-(beta-aminoethylether) N, N+ tetra acetic acid (EGTA) (2mM), alpha,alpha-dipyridyl (500 microM) and 1,10-orthophenanthroline (200 microM). The sensitivity of the reaction to alpha,alpha-dipyridyl and 1,10-orthophenanthroline suggested the involvement of Fe2+ in the reaction. Inhibition of enzyme activity by EGTA and restoration of activity by supplementation of CaCl2 to the EGTA-dialysed sample confirmed the absolute requirement for calcium for this activity. Calcium was absent in the EGTA-dialysed enzyme. Apart from these inhibitors, NaF and NH2OH were potent inhibitors of the enzyme reaction.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Isolation of 34 kDa protein from spinach chloroplasts having ferrooxidase and H2O2-dependent dark O2 evolution activities. 205 97

In previous publications, one of us demonstrated that variation in paramagnetic-ion contents is a major contributing factor to the different NMR relaxation times, T1 and T2, of water protons among normal mouse tissues; and between normal tissues and cancer cells. The nature of the paramagnetic ions involved was not determined. In the present communication, we report results of analysis of the contents of three biologically prominent paramagnetic ions (manganese, iron and copper) in 9 normal mouse tissues (brain, heart, small intestine, kidney, liver, lung, voluntary muscle, spleen and stomach); one strain of rat cancer cells (As-30, rat hepatoma); and 6 strains of mouse cancer cells (Ehrlich mammary adenocarcinoma, LSA lymphoma, Krebs carcinoma of the inguinal region; sarcoma 180; Klein TA3 mammary adenocarcinoma; P815 mast cell leukemia). Our data indicate that manganese and iron are by far the two most important paramagnetic ions contributing to the diversity of NMR relaxation times. The average manganese content of all the normal mouse tissues studied (29.6 +/- 4.99 mu mole/kg) is 24 times higher than the average manganese contents of all the cancer cells studied (1.22 +/- 0.27 mu moles/kg) and there is essentially no overlap between the two groups of data. The average iron content of the normal mouse tissues (281.6 +/- 51.2 mumoles/kg) is 4 times the average in cancer cells (66.7 +/- 7.74 mumoles/kg) but there is some overlap here. The observed differences in both the manganese and iron contents are statistically highly significant, with P's below 0.0001. The copper contents of the cancer cells is lower than the average of normal mouse tissues but only by some 20%. The difference is statistically insignificant at the 0.05 level but significant at the 0.2 level.
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PMID:Low paramagnetic-ion content in cancer cells: its significance in cancer detection by magnetic resonance imaging. 159 62


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