Reduction of substituted flavins by .CO2- and cyclic disulphide anions

5-Deazariboflavin was observed to undergo one electron-equivalent reduction on reaction with .CO2-, DS2-. or a mixture of .CO2- and eaq-. This is attributed to formation of .FlH, followed by dimerization: 2 5-DRFlH.----(5-DRFlH)2 a process not previously confirmed. In contrast, 3-deazariboflavin, 1-deazariboflavin 7-chlororiboflavin, 2-thioriboflavin, lumiflavin, flavin adenine dinucleotide and riboflavin all underwent two electron-equivalent reductions to FlH2 or FlH-species via the disproportionation: 2.FlH----FlH2+Fl Spectra of the reduced species are reported for 3-deazariboflavin, 1-deazarboflavin and 2-thioriboflavin. The anion radicals of dithiothreitol (DS2-.) and lipoamide (LS2-.) did not effect reduction beyond the two electron equivalence point. However, .CO2- was seen to effect further reactions with the dihydroforms of the higher redox potential flavins 7-chlororiboflavin and 2-thioriboflavin at pH 3 to 10, but for the other flavins only at or below pH 2. Except for the sulphur-containing 2-thioriboflavin, the protonated DS2.H and LS2.H radicals were unable to reduce any of the flavins at pH less than or equal to 3. This cause a 'falloff' in the yield of the reduced flavin which is in accord with the reaction rate constants and radical pK values. Despite their differences in absorbance, the reactions of DS2.H and LS2.H towards flavins were similar in all aspects examined. Several new rate constants are reported.     

Reduction of ubiquinone by lipoamide dehydrogenase. An antioxidant regenerating pathway.

Lipoamide dehydrogenase belongs to a family of pyridine nucleotide disulfide oxidoreductases and is ubiquitous in aerobic organisms. This enzyme also reduces ubiquinone (the only endogenously synthesized lipid-soluble antioxidant) to ubiquinol, the form in which it functions as an antioxidant. The reduction of ubiquinone was linear with time and exhibited turnover numbers of 5 and 1.2 min(-1) in the presence and absence of zinc, respectively. The reaction was stimulated by zinc and cadmium but not by the other divalent ions tested. The zinc/cadmium-dependent stimulation of the reaction increased rapidly and linearly up to a concentration of 0.1 mM and was even further increased at 0.5 mM. At pH 6, the activity was three times higher than at physiological pH. Alteration of the NADPH : NADP(+) ratio revealed that the reaction is inhibited by higher concentrations of the oxidized cofactors. FAD reduced ubiquinone in a dose-dependent manner at a considerably lower rate, suggesting that the reduction of ubiquinone by lipoamide dehydrogenase involves the FAD moiety of the enzyme.     

Fast repair of dAMP radical anions by phenylpropanoid glycosides and their analogs

Repair effect on 2'-deoxyadenosine-5'-monophosphate (dAMP) radical anions by phenylpropanoid glycosides (PPGs) and their analogs, isolated from Chinese folk medicinal herb, was studied using pulse radiolysis technique. The radical anion of dAMP was formed by the reaction of hydrated electron with dAMP. On pulse irradiation of nitrogen-saturated dAMP aqueous solution containing 0.2 M t-BuOH and one of PPGs or their analogs, the transient absorption spectrum of the radical anion of dAMP decayed with the formation of that of the radical anion of PPGs or their analogs within several decades of microseconds after electron pulse irradiation. The results indicated that dAMP radical anions can be repaired by PPGs or their analogs. The rate constants of the repair reactions were deduced to be 1.6-4.5 x 10(8) M(-1) s(-1).     

Generation of radical anions of nitrofurantoin, misonidazole, and metronidazole by ascorbate

Nitrofurantoin, misonidazole, and metronidazole were reduced to their corresponding nitro anion radicals by ascorbate in anaerobic solutions at high pH. The nitrofurantoin anion radical could be detected at neutral pH. In neutral solutions, the nitro anion radicals of misonidazole and metronidazole were too unstable to be observed by electron spin resonance spectroscopy. At neutral pH, solutions containing ascorbate, nitrofurantoin, or misonidazole consumed oxygen. The addition of superoxide dismutase, catalase, or both superoxide dismutase and catalase decreased the rate of oxygen consumption. These results show that nitro anion radicals are formed by reduction with ascorbate, and superoxide anion radical and hydrogen peroxide are produced by reactions of these radicals with oxygen.     

半连续及连续培养小球藻减排沼液及CO2

采用半连续或连续模式培养小球藻,考察小球藻减排沼液和CO2的能力。结果表明:在半连续培养模式中,当更新率为30%时,沼液中的N、P质量浓度可分别稳定在16～18和0.4～0.6 mg/L,达到污水二级排放标准;提高更新率到40%以上,3 d后微藻生物量及其对沼液中N、P的吸收达到动态平衡,但N、P去除率未达到污水直接排放标准;在连续培养模式中,分别选用20%及30%的日更新率,7 L规模12 d后沼液中的总氮(TN)仍高达55.64 mg/L。说明大规模培养条件下的光限制是微藻法减排沼液的主要制约因素。     

CO2 Reduction to Formate in Clostridium acidi-urici

Cell-free lysates of Clostridium acidi-urici catalyze the reduction of CO(2) to formate in the presence of reduced ferredoxin and nicotinamide adenine dinucleotide, reduced form.     

Reduction of cytochrome C by ascorbic free radical.

The rate of "in vivo" reduction of cytochrome c by ascorbic acid (AA) increases from 69 nmoles of cytochrome c for minute, to 202 nanomoles when ascorbate oxidase is added. Since the AA oxidation by AA oxidase is a system to generate ascorbic free radical (AFR), data suggest that AFR is a better reducing compound than ascorbate in cytochrome c reduction. Since the addition of oxidized glutathione and human immunoglobulins (-S-S- bridge containing compounds) in the medium produces a remarkable decrease in cytochrome c reduction, it is suggested that AFR could also reduce -S-S- groups.     

Ultraviolet radiation-induced photodegradation and 1O2, O2-. production by riboflavin, lumichrome and lumiflavin

Although UVA (320-400 nm) is considered less harmful to skin as compared to UVB (290-320 nm) and UVC (200-290 nm) radiation, certain endogenous chromophores may enhance UVA-induced cutaneous reactions by largely O2-dependent photodynamic reactions. Photodegradation pattern and singlet oxygen (1O2), superoxide anion radical (O2-.) producing capacity of riboflavin (RF), lumiflavin (LF) and lumichrome (LC) were examined to assess their phototoxic potential under UVA. Photolysis of RF upon exposure to UVA, UVB or UVC revealed considerable degradation to LF and LC with a near identical spectral pattern of photodegradation between 250-500 nm. Both LF and LC were stable to UVA (3 J/cm2) and UVB (400 mJ/cm2), whereas RF was photodegraded by 30 and 20%, respectively, under similar irradiation conditions. UVA-sensitized LF and LC respectively, produced nearly 15% higher and 60% lower yield of 1O2 in comparison to RF, whereas, O2-. was generated predominently by RF. Both RF and LF thus appeared to be potential chromophores for evoking deleterious effects of UVA in normal human skin.     

Reduction of Respiration by High Ambient CO2 and the Resulting Error in Measurements of Respiration Made with O2 Electrodes

Respiration rates of Lemna gibba fronds and Orobanche aegyptiacaand Lactuca sativa seedlings, were measured with a Clark typeoxygen electrode in the presence or absence of a carbon-dioxideabsorber (KOH) in the gas phase. Measured respiration ratesin the presence of KOH were 17-34% higher than in its absence.The suppression of respiration by high CO₂ concentrations, [CO₂],was confirmed by parallel studies of CO₂ efflux, made by infraredgas spectrometry. These results are consistent with other reportsof reduced rates of respiration at high [CO₂]. Measurements of respiration quotients of Lemna and Lactuca weremade at 0 and 100 Pa [CO₂]. Results did not support the possibilityof induced dark fixation of CO₂ at the ambient atmospheric [CO₂]predicted for the next century (35-100 Pa). It is concluded that the numerous reports of respiration measurementsmade with O₂ electrodes, in the absence of a CO₂ absorber, maycontain a significant errorCopyright 1993, 1999 Academic Press Lemna gibba, Lactuca sativa, Orobanche aegyptiaca, CO₂ accumulation, O₂ electrode, respiration, dark CO₂ fixation, respiration quotient, atmospheric CO₂     

Generation of radical anions from metronidazole, misonidazole and azathioprine by photoreduction in the presence of EDTA

Ultraviolet irradiation of the nitroimidazole derivatives metronidazole, misonidazole, azathioprine and 1-methyl-4-nitroimidazole in aqueous solution with various reductants produced the respective nitro radical anions, as detected by electron spin resonance spectroscopy. The most effective reductant, yielding high concentrations of the radical anions, was EDTA at pH 10. NADH, NADPH, formaldehyde glutathione and methanol were also tested but were less efficient as reductants.     

Low CO(2) Prevents Nitrate Reduction in Leaves

The correlation between CO₂ assimilation and nitrate reduction in detached spinach (Spinacia oleracea L.) leaves was examined by measuring light-dependent changes in leaf nitrate levels in response to mild water stress and to artificially imposed CO₂ deficiency. The level of extractable nitrate reductase (NR) activity was also measured. The results are: (a) In the light, detached turgid spinach leaves reduced nitrate stored in the vacuoles of mesophyll cells at rates between 3 and 10 micromoles per milligram of chlorophyll per hour. Nitrate fed through the petiole was reduced at similar rates as storage nitrate. Nitrate reduction was accompanied by malate accumulation. (b) Under mild water stress which caused stomatal closure, nitrate reduction was prevented. The inhibition of nitrate reduction observed in water stressed leaves was reversed by external CO₂ concentrations (10-15%) high enough to overcome stomatal resistance. (c) Nitrate reduction was also inhibited when turgid leaves were kept in CO₂-free air or at the CO₂-compensation point or in nitrogen. (d) When leaves were illuminated in CO₂-free air, activity of NR decreased rapidly. It increased again, when CO₂ was added back to the system. The half-time for a 50% change in activity was about 30 min. It thus appears that there is a rapid inactivation/activation mechanism of NR in leaves which couples nitrate reductase to net photosynthesis.     

Reduction of CO2 by a high-density culture of Chlorella sp. in a semicontinuous photobioreactor

The microalga incorporated photobioreactor is a highly efficient biological system for converting CO2 into biomass. Using microalgal photobioreactor as CO2 mitigation system is a practical approach for elimination of waste gas from the CO2 emission. In this study, the marine microalga Chlorella sp. was cultured in a photobioreactor to assess biomass, lipid productivity and CO2 reduction. We also determined the effects of cell density and CO2 concentration on the growth of Chlorella sp. During an 8-day interval cultures in the semicontinuous cultivation, the specific growth rate and biomass of Chlorella sp. cultures in the conditions aerated 2-15% CO2 were 0.58-0.66 d(-1) and 0.76-0.87 gL(-1), respectively. At CO2 concentrations of 2%, 5%, 10% and 15%, the rate of CO2 reduction was 0.261, 0.316, 0.466 and 0.573 gh(-1), and efficiency of CO2 removal was 58%, 27%, 20% and 16%, respectively. The efficiency of CO2 removal was similar in the single photobioreactor and in the six-parallel photobioreactor. However, CO2 reduction, production of biomass, and production of lipid were six times greater in the six-parallel photobioreactor than those in the single photobioreactor. In conclusion, inhibition of microalgal growth cultured in the system with high CO2 (10-15%) aeration could be overcome via a high-density culture of microalgal inoculum that was adapted to 2% CO2. Moreover, biological reduction of CO2 in the established system could be parallely increased using the photobioreactor consisting of multiple units.     

Spin trap evidence for production of superoxide radical anions by purified NADPH-cytochrome P-450 reductase

Previous evidence for superoxide radicals as initial reduction products of oxygen by NADPH cytochrome P-450 reductase has been indirect. In this paper a technique is described to spin trap radicals produced in incubations of oxygen and reductase. Reference spin trap adducts were synthesized by adding phenyl-$\text{t}$-butyl nitrone (PBN) to superoxide radicals (PBN-OOH) or to hydroxyl radicals (PBN-OH). Both PBN adducts are stable in water or ethyl acetate for hours. Electron Paramagnetic Resonance (EPR) spectra measured in N₂-saturated ethyl acetate allow clear resolution of the hyperfine extrema of PBN-OH and PBN-OOH (2.1 and 4.5 G splitting, respectively). Comparison of EPR spectra from reductase and oxygen incubations with those of synthetic PBN-OOH suggest that superoxide radicals are the major primary reduction product of oxygen.     

Effects of temperature and CO2 concentration on photosynthetic CO2 fixation by Chlorella

The rates of photosynthetic ¹⁴CO₂ fixation by Chlorella vulgarisllh, grown under high CO₂, were determined between 4 to 37°Cwith air containing from 300 to 13,000 ppm ¹⁴CO₂. When the CO₂level was increased, both the rate of photosynthesis and theoptimum temperature for maximum photosynthesis increased. Themaximum photosynthetic rate was reached at 12°C with 300ppm ^l4CO₂. Among the photosynthetic products fromed at 300 ppm ¹⁴CO₂, glycolatedecreased greatly when the temperature was raised from 20 to30°C. At 3,000 ppm ¹⁴CO₂ an insignificant amount of glycolatewas formed at all temperatures, whereas ¹⁴C-incorporation intothe insoluble fraction, sucrose, and the lipid fraction wassignificantly higher than at 300 ppm ¹⁴CO₂. The ¹⁴C in sucrosewas greatly increased and the radioactivity in the insolublefraction decreased when the temperature was raised from 28 to36°C. (Received April 8, 1980; )     

Radiation damage to the erythrocyte membrane in the presence of radical anions. I

Irradiated porcine erythrocytes demonstrated increased osmotic fragility, which was enhanced by the addition of anions. The extent of the damage produced by the secondary radicals depended on the kind of anion and conditions of irradiation. The most pronounced changes occurred in the presence of azide, whereas bromide and thiocyanate gave rise to a smaller enhancement of osmotic fragility. Irradiation of cells in air or N2O revealed that radical anions have more damaging effects on porcine erythrocytes in air.