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51.
Acetylene inhibition technique underestimates in situ denitrification rates in intact cores of freshwater sediment 总被引:5,自引:0,他引:5
Abstract Denitrification in intact sediment cores was measured by the acetylene inhibition technique and compared with the nitrate flux between water and sediment. Less than half of the nitrate-N consumed by the sediment could be recovered as nitrous oxide-N. The low recovery rate of nitrous oxide from intact sediment cores indicated losses of nitrous oxide by diffusion down to nitrate-free sediment layers, where reduction of nitrous oxide may take place. In sediment slurries 100% of nitrate-N could be recovered as nitrous oxide-N as long as the nitrate concentration in the liquid phase was above 10 μM. Nitrous oxide added to nitrate-free sediment slurries was reduced regardless of whether acetylene was present or not. Therefore denitrification may be significantly underestimated by this method. 相似文献
52.
Øivind Løvstad 《Hydrobiologia》1986,134(3):201-206
Population densities and total phosphorus concentrations in samples from different lakes of south-eastern Norway were determined. In addition some transplant experiments with dilute phytoplankton populations were carried out. A laboratory batch culture method was used.The diatoms studied may be divided into three ecological groups based on their cell densities and total phosphorus concentrations in the samples. This classification was supported by the experimental results.
Cyclotella spp., Asterionella formosa and Tabellaria fenestrata did not grow or had low growth rates above pH 9. Synedra cf. acus and Fragilaria crontonensis had often high growth rates within the pH 9–10 range, but were not able to grow at pH values above 10. High pH-values had no effect on the growth rate of Oscillatoria.
Oscillatoria, Synedra and Stephanodiscus were severely growth-limited in filtered water from oligotrophic lakes. Maximum growth rates of all the populations studied were often obtained after addition of phosphate and chelated iron (FeEDTA) in combination to filtered water samples from oligotrophic/mesotrophic lakes. 相似文献
53.
Early iron deficiency in rat does not affect the weight or the protein, DNA, and RNA content but results in a slight reduction in gamma-aminobutyric acid (GABA) (13%, p less than 0.01) and glutamic acid (20%, p less than 0.001) content of the brain. The activities of the two GABA shunt enzymes, glutamate dehydrogenase and GABA-transaminase, and of the NAD+-linked isocitrate dehydrogenase (ICDH) were inhibited whereas the glutamic acid decarboxylase, mitochondrial NADP+-linked ICDH, and succinic dehydrogenase activities remained unaltered in brain. On rehabilitation with the iron-supplemented diet for 1 week, these decreased enzyme activities in brain attained the corresponding control values. However, the hepatic nonheme iron content increased to about 80% of the control, after rehabilitation for 2 weeks. A prolonged iron deficiency resulting in decreased levels of glutamate and GABA may lead to endocrinological, neurological, and behavioral alterations. 相似文献
54.
Richard W. Hendler Barry Bunow John S. Rieske 《Journal of bioenergetics and biomembranes》1985,17(1):51-64
In coenzyme Q-cycles, it is proposed that one electron from the quinol reduces the Rieske iron sulfur center (E
m280 mV) and the remaining electron on the semiquinone reduces cytochromeb
T (E
m–60 mV). TheE
mfor the two-electron oxidation of the quinol is 60 mV and therefore the reduction of cytochromeb
T by quinol is not favorable. As the stability constant for the dismutation of the semiquinone decreases, the calculatedE
mfor the Q/QH couple is lowered to values below theE
mof cytochromeb
T. Contemporary coenzyme Q-cycles are based on the belief that the lower value for theE
mof the Q/QH couple compared to theE
mfor cytochromeb
T means that the semiquinone is a spontaneous reducing agent for theb-cytochrome. The analysis in the paper shows that this is not necessarily so and that neither binding sites nor ionization of the semiquinoneper se alters this situation. For a Q-cycle mechanism to function,ad hoc provisions must be made to drive the otherwise unfavorable reduction of cytochromeb
T by the semiquinone or for the simultaneous transfer of both electrons to cytochromeb
T and cytochromec
1 (or the iron sulfur protein). Q-cycle mechanisms with these additional provisions can explain the observation thus far accumulated. A linear path which is functionally altered by conformational changes may also explain the data. 相似文献
55.
56.
Cytochrome c oxidase preparations from bovine heart muscle contain 1 zinc per 2 irons. Metal contents of nine preparations determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) show that Cu, Fe and Zn are the only metals present in significant amounts with average Cu/Fe, Fe/Zn, and Cu/Zn atom ratios of 1.3, 2.1 and 2.8, respectively. Removal of adventitious copper results in a Cu:Fe:Zn stoichiometry of 2:2:1. The zinc is tightly bound. Dialysis against a solution of 1,10-phenanthroline at pH 7.4 or an acidic buffer (pH 4.4) does not remove Zn. Dialysis against 0.8 M KCN at pH 10 causes partial loss of both Cu and Zn. This is the first evidence for the presence of Zn in a cytochrome c oxidase. 相似文献
57.
Evidence is presented here that axenic cultures of Nostoc spp., Aphanocapsa (PCC 6308), and Aphanocapsa (PCC 6714) but not Anacystis nidulans R-2 (PCC 7942) produce N2O and ammonia when grown on nitrite. The data suggest that the cyanobacteria produce N2O by nitrite reduction to ammonia.Nonstandard abbreviations DCMU
3-(3,4-dichlorophenyl)-1,1-dimethyl urea
- NIR
nitrite reductase 相似文献
58.
Abstract The first step of aerobactin biosynthesis, oxidation of an aliphatic primary amino group to an N -hydroxy-amino compound seems to be involved in the biosynthesis of most of the hydroxamatetype siderophores which are widely distributed among bacteria and fungi. Therefore, the first step of aerobactin biosynthesis, oxidation of lysine to N 6 -hydroxylysine was studied as a model reaction using a strain of Escherichia coli that contains the first gene aerA of aerobactin synthesis on a multi-copy plasmid and which is lacking the gene for the subsequent step in the pathway. In addition, culture conditions are described which lead to the secretion of N 6 -hydroxylysine into the medium in amounts that can easily be quantitatively determined by a simple, reliable chemical assay. This assay can be used for screening inhibitors of the oxidation of α-amino groups, which should interfere with the biosynthesis of siderophore hydroxamates and thus should create bacteriostatic conditions. 相似文献
59.
Aerobic ferrisiderophore reductase assay and activity stain for native polyacrylamide gels 总被引:4,自引:0,他引:4
The reduction of ferric iron from microbial iron-binding compounds (siderophores) releases the iron from the siderophore so that it may be utilized by the microorganism. A method to detect aerobic ferrisiderophore reductase activity using ferrozine as a ferrous iron trap is shown to be applicable to cytoplasmic fractions from Rhodopseudomonas sphaeroides and four other different species of bacteria. The ferrisiderophore reductase uses reduced nicotinamide cofactors as reducing agents, and activity is stimulated by flavins. This assay has been adapted as a staining method to locate ferrisiderophore reductase activity in native polyacrylamide gels. 相似文献
60.
Saroj Sanan Geeta Sharma Rakesh Malhotra Devindar P. Sanan Parveen Jain Prem Vadhera 《Free radical research》1989,6(1):29-38
Haemorrhagic shock was produced in anaesthetized dogs, by rapid arterial bleeding to mean arterial blood pressure 35 mmHg, and maintained oligaemic for 4 h followed by return of withdrawn blood(R0WB). Dogs were observed for 72 h after ROWB for survival and recovery, and, for histopathological (HP) studies on liver, dogs were sacrificed 2 h after ROWB in non-survival experiments. Desferrioxamine mesylate (25mg/kg) was administered intra-muscularly at 2,3 and 4h after blood loss in survival experiments and for HP studies the drug was given at 4 h in one group and at 2 h plus 4 h after blood loss in the second group. With the drug given at 3 or 4h, survival was 70% and 100% while in the 2h and the untreated groups it was 50%. Recovery was rapid in all the drug treated survivors, few became conscious within 30min. showed slight activity by 4-6 h, all were almost normally active by 24 and fully so by 72 h after ROWB. All the 5 control survivors remained unconscious/drowsy upto 24 h; 3 were sluggish at 72 h. By group analysis, serum iron elevation during the oligaemic and at the end of the post-oligaemic phase was less in the drug-treated animals. HP changes of shock in the liver studied by light microscopy, were markedly reduced in severity and were less prevalent in the drug-treated dogs. The salutory effects of desferrioxamine may be due to inhibition of iron catalyzed free-radical production and tissue damage, through its strong iron chelating action. It may have a therapeutic advantage in this emergency condition without the disadvantages of toxicity inherent in prolonged use. 相似文献