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1.
The phenomenon of hemoglobin-facilitated O2 diffusion was studied by a polarographic method.

Polarograms relative to the reduction process of O2 have been obtained at pH 7.2 (phosphate buffer, 30°) in the presence of various hemoglobin concentrations (Hbtot*) and at various O2 partial pressures (from 8 to 360 mm Hg).

Analogous experiments were performed at pH 6.4 and 8.1 (at constant ionic strength). Graphs of the limiting current values (at E = −1.5 V versus the saturated calomel electrode), relative to the overall reduction process of oxygen, plotted versus PO2 (at Hbtot* = constant), show some characteristic trends. The influence of pH on the features of the experimental curves is discussed.

Experimental results suggest that the diffusions of O2, oxyhemoglobin and hemoglobin, as well as the kinetics of dissociation and association of O2 with hemoglobin, are effective in determining the “facilitated flux”.

The corresponding nonlinear differential system is solved under some simplifying assumptions, and an expression for the flux, and consequently for the current, is obtained which is consistent with the experimental findings.

Furthermore, it is shown that the dissociation curve of oxyhemoglobin can be obtained from these polarographic experiments on the basis of this theory. Agreement with tensiometric data was satisfactory.  相似文献   


2.
Cyclic voltammetry at a micro electrode of Co(II) salen, Fe(II) salen, electrode generated Fe(II)(acac)2, Fe(II) (salicylaldehyde)2, Fe(II) (salicylaldoxime)2, Fe(II) (bipy)3, Fe(II) (bipy)2, Co(II) (bipy)3, Co(II) (benzacac)2, and electrode generated Co(acac)2 in oxygen saturated aprotic solvents show positive shift of the O2 sigmoidal wave, as well as enhancement of the limiting current in the case of the first five compounds. In the case of Co(II) (bipy)3 the slope of the sigmoidal wave due to O2 becomes more positive, while for the other two Co(II) complexes there is no change except a small decrease in the wave height. The data are used to correlate and predict the O2 binding properties of the chelates in solution. The data for the diketone complexes of Co(II) indicate absence of any direct association, which is in line with the interpretation offered in the literature on the mechanism of their catalytic role in the O2 oxidation of substrates. The mechanism of the autoxidation of dimethylformamide in the presence of Fe(III) (bipy)3 and Cu(II) (bipy)2 is elucidated by the observation that these higher valent compounds are reduced to their next lower oxidation state by DMF.  相似文献   

3.
Gilles Peltier  Jacques Ravenel 《BBA》1987,894(3):543-551
When dark-adapted (5 min in the dark) Chlorella cells were deposited on a bare platinum electrode, treated with DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) and illuminated, O2 was consumed after a lag time of about 250 ms. The comparison of the O2 consumption kinetics with the fluorescence O-I-D-P-S transition (the fast change in chlorophyll fluorescence which occurs after the onset of illumination of dark-adapted algae and is over within 2 s) observed in untreated algae indicates that no O2 is consumed during the fluorescence rise and that O2 uptake is initiated approximately when the maximum level of fluorescence P is reached. Mass spectrometry measurements of O2 exchange (using 18O2) were performed during dark to light transition with DCMU-untreated Chlorella cells. Under these conditions, O2 reduction began after a lag time (about 200–400 ms) and stopped after about 5 s of illumination. The above experiments clearly show that the reduction of O2 starts nearly at the same time that the fluorescence P-S decline. On the other hand, we show that the reduction of CO2 does not interfere in the fluorescence O-I-D-P-S transient. We found the same apparent affinity for O2 (about 57 μM) for both the fluorescence P-S decline and the reduction of O2. At least three consecutive short (2 μs) saturating flashes were required to affect the fluorescence transient significantly and also to induce a significant uptake of O2. Moreover, parabenzoquinone, an artificial Photosystem I electron acceptor, inhibited both the fluorescence D-P rise and the 250 ms lag time observed in the reduction of O2. We conclude from the above results that in the early stages of the illumination of dark-adapted algae, some Photosystem I electron acceptors are in an inactive form. In this form, the electron transport chain is unable to reduce either O2 or CO2. This would lead to the accumulation of electrons on the Photosystem II acceptors (principally QA and the plastoquinone pool) and therefore explains the fluorescence D-P rise. The light activation, probably achieved through the reduction of at least two electron acceptors, first allows the reduction of O2, and therefore explains the P-S fluorescence decline. By accepting electrons before the site of regulation and mediating rapid O2 reduction, parabenzoquinone avoids the accumulation of electrons and therefore inhibits the D-P fluorescence rise.  相似文献   

4.
5.
Y. Mathieu 《BBA》1969,189(3):411-421
Influence of oxygen on the electron transfers of photosynthesis. I. Influence of some oxygen concentrations on some Hill reactions

The influence of O2 concentrations on the Hill reactions in the presence of p-benzoquinone, ferricyanide, NADP+, NADP+ plus ferredoxin has been studied with isolated spinach chloroplasts.

Because of the partial reoxidation of the hydroquinone, which is depending upon the O2 concentration, it does not seem possible to localize a site of action for O2.

With ferricyanide the influence of O2 is weak. However, the rate of ferricyanide reduction is increased in the presence of O2. The observed stimulation is greater for 21% O2 than for 70% O2. Bicarbonate stimulates the ferricyanide reduction and decreases the stimulating effect of 21% O2.

O2 decreases the rate of NADP+ reduction. Ferredoxin as well as bicarbonate stimulate the NADP+ reduction and reduce the O2 inhibition.

These results seem to indicate that O2 may enter the electron transport chain at a site situated near Photosystem I and before the ferredoxin's site.

The inhibitory effect of O2 on the Hill reactions with p-benzoquinone and NADP+ is depending upon the plants' growth conditions. It is greater with plants grown under weak light.  相似文献   


6.
Human neutrophils (PMN) activated by N-formyl-methionyl-leucyl-phenylalanine (fMLP) simultaneously release nitric oxide (.NO), superoxide anion (O2-) and its dismutation product, hydrogen peroxide (H2O2). To assess whether NO production shares common steps with the activation of the NADPH oxidase, PMN were treated with inhibitors and antagonists of intracellular signaling pathways and subsequently stimulated either with fMLP or with a phorbol ester (PMA). The G-protein inhibitor, pertussis toxin (1-10 μg/ml) decreased H2O2 yield without significantly changing. NO production in fMLP-stimulated neutrophils; no effects were observed in PMA-activated cells. The inhibition of tyrosine kinases by genistein (1-25 μg/ml) completely abolished H2O2 release by fMLP-activated neutrophils; conversely, NO production increased about 1.5- and 3-fold with fMLP and PMA, respectively. Accordingly, orthovanadate, an inhibitor of phosphotyrosine phosphatase, markedly decreased -NO production and increased O2;- release. On the other hand, inhibition of protein kinase C with staurosporine and the use of burst antagonists like adenosine, cholera toxin or dibutyryl-cAMP diminished both H2O2 and NO production. The results suggest that the activation of the tyrosine kinase pathway in stimulated human neutrophils controls positively O2- and H2O2 generation and simultaneously maintains -NO production in low levels. In contrast, activation of protein kinase C is a positive modulator for O2;-and *NO production.  相似文献   

7.
目的: 观察急性间歇性低氧刺激后大鼠颈动脉体对低氧的敏感性以及多巴胺对颈动脉体低氧敏感性的影响。方法: 将分离SD大鼠的颈动脉体-窦神经移入到孵育槽,然后把分离的窦神经吸入到记录的玻璃电极中行电信号记录。记录基线部分缓冲液充入气体为95% O2+ 5% CO2混合气,低氧应激给予5% O2+ 5% CO2+ 90% N2混合气,低氧刺激给予30 s,95% O2 + 5% CO2给予90 s,共10个循环,每组实验大鼠数量n大于等于5。结果: 大鼠离体的颈动脉体,给予急性间歇性低氧应激,再给予低氧刺激,窦神经较之前低氧刺激放电活动增强。但加入多巴胺后,可以抑制窦神经对低氧的反应,急性间歇性低氧后,多巴胺对窦神经的低氧放电活动抑制作用加强。结论: 大鼠颈动脉体给予急性间歇性低氧可增强窦神经对低氧的反应,多巴胺可抑制急性低氧诱导的颈动脉体对低氧敏感性的增强。  相似文献   

8.
E. K. Pistorius  G. H. Schmid 《BBA》1987,890(3):352-359
The roles of Ca2+ and Cl on the photosynthetic O2 yield under flash illumination have been examined in EDTA-washed preparations of the cyanobacterium Anacystis nidulans. Especially the effect of Cl deficiency on the O2 yield and on the S-state distribution was analyzed. As the results show, omission of both Ca2+ and Cl (Mn2+ present) almost totally inhibited O2 evolution. When Ca2+ was replaced by Na+, a substantial reduction of the O2 yield was observed, but only a minor change in the S-state distribution occurred. However, when Cl was displaced by NO3, which is equivalent to Cl deficiency of the water-splitting complex, a substantial reduction of the O2 yield and in addition a significant change in the S-state distribution was observed. The comparison of deactivation kinetics in NO3 containing samples with those in control samples indicated that Cl deficiency allowed accumulation of oxidizing equivalents up to the S3 state but modified the final step of O2 evolution. Moreover, those centers which advanced to the S3 state in the absence of Cl deactivated in a special way which involved a faster deactivation of S2 and an increased formation of S−1.  相似文献   

9.
Nam-Hai Chua 《BBA》1971,245(2):277-287
1. The methyl viologen-catalyzed Mehler reaction was investigated in intact cells of five species of blue-green algae and Chlamydomonas reinhardi.

2. In the presence of methyl viologen, all the blue-green algae except Anabaena flos-aquae show a light-dependent O2 consumption as well as a post-illumination O2 evolution. The rate of O2 consumption is stimulated by 1 mM KCN, an inhibitor of catalase, but the dark O2 evolution becomes suppressed.

3. A. flos-aquae shows a light-dependent methyl viologen-catalyzed O2 uptake which is not affected by 1 mM KCN. Furthermore, there is no release of O2 in the dark following illumination.

4. With C. reinhardi, the cells do not show any net O2 exchange during or after illumination. Addition of 1 mM KCN, however, results in an immediate O2 uptake in the light.

5. Based on the mechanism postulated for the Mehler reaction in isolated chloroplasts, it was deduced that the differences in the kinetics of the O2 exchange catalyzed by methyl viologen reflect differences in the endogenous catalase activity in these algae. Cells of A. flos-aquae are deficient in catalase activity whereas those of the other blue-green algae possess catalase, although at low activity. C. reinhardi, on the other hand, has high catalase activity in vivo.

6. These findings are corroborated by results obtained from O2 electrode measurements of catalase activity in cell-free extracts of these algae.

7. The possible roles of catalase in algae and the implications of these results are also discussed.  相似文献   


10.
O2 generation in mitochondrial electron transport systems, especially the NADPH-coenzyme Q10 oxidoreductase system, was examined using a model system, NADPH-coenzyme Q1-NADPH-dependent cytochrome P-450 reductase. One electron reduction of coenzyme Q1 produces coenzyme Q1 and O2 during enzyme-catalyzed reduction and O2 + coenzyme Q1 are in equilibrium with O2 + coenzyme Q1 in the presence of enough O2. The coenzyme Q1 produced can be completely eliminated by superoxide dismutase, identical to bound coenzyme Q10 radical produced in a succinate/fumarate couple-KCN-submitochondrial system in the presence of O2. Superoxide dismutase promotes electron transfer from reduced enzyme to coenzyme Q1 by the rapid dismutation of O2 generated, thereby preventing the reduction of coenzyme Q1 by O2. The enzymatic reduction of coenzyme Q1 to coenzyme Q1H2 via coenzyme Q1 is smoothly achieved under anaerobic conditions. The rate of coenzyme Q1H2 autoxidation is extremely slow, i.e., second-order constant for [O2][coenzyme Q1H2] = 1.5 M−1 · s−1 at 258 μM O2, pH 7.5 and 25°C.  相似文献   

11.
平琴  徐胜  陈玮  何兴元  黄彦青  吴娴 《生态学杂志》2017,28(12):3862-3870
通过开顶箱(OTCs)模拟,以环境臭氧(O3)浓度约40 nmol·mol-1为对照,研究大气O3浓度升高(80和160 nmol·mol-1O3)对冷季型草坪草高羊茅生长、亚细胞结构及其活性氧代谢的影响.结果表明: 14 d的80 nmol·mol-1O3熏蒸使高羊茅株高和叶宽降低,总生物量降低43.7%,老叶变黄,而160 nmol·mol-1O3处理高羊茅叶出现大量枯死褐斑,叶尖坏死,新叶卷曲,总生物量降低46.2%,叶肉细胞膜卷曲,叶绿体和线粒体受损严重.与对照相比,80和160 nmol·mol-1O3熏蒸下高羊茅叶片超氧阴离子(O2)产生速率、过氧化氢(H2O2)和丙二醛(MDA)含量显著增加,抗氧化酶活性显著升高,但叶片总酚含量和抗氧化能力随O3浓度升高而先升高后降低.在明显O3伤害症状出现之前,O3已对高羊茅的生长和抗氧化代谢产生不利影响;高羊茅抗氧化系统虽对O3浓度的升高存在一定的适应性反应,但其不能抵御过高浓度的长期胁迫和伤害.  相似文献   

12.
In 25-day-old rats, injected intraperitoneally with 0.2 ml aliquots of 6% methylene blue in saline over 1 hr followed by a single 4-6 ml intra-arterial injection; O2 pressurized to 45 lb/in2 was used to improve reblueing of 1.5-2 mm slices of cerebellum, thus increasing staining selectivity. Factors believed to influence this selectivity for axonal elements and fine dendrites are the rapidity and pressure (about 300 mm Hg) of the terminal intra-arterial injection, the hyperbaric O2 treatment of tissue slabs for 1 hr as a substiute for room air, and immersion in 6% ammonium molybdate for 1 hr before return to atmospheric conditions.  相似文献   

13.
Anhydrous Zn(O3SCF3)2 and Zn(O2CCX3)2, X=F, Cl, Br were obtained in substantially quantitative yields from ZnO (or ZnEt2 in the case of the bromide derivative) and a mixture of the corresponding acid and anhydride in heptane as medium. The reactions are rapid and moderately exothermic. Recrystallization of the triflate and trifluoroacetate complexes from dimethoxyethane (DME) produced single crystals of Zn(O3SCF3)2(DME)2 (1) and [Zn(O2CCF3)2(DME)]n (2) suitable for X-ray diffraction studies. In both compounds zinc is hexacoordinated with a pseudo-octahedral geometry. Compound 1 is constituted by mononuclear molecules with terminal monodentate O3SCF3 ligands in trans position. A polynuclear chain structure was found for 2 with zinc atoms joined alternatively by triple and single carboxylato bridges, and with bidentate terminal DME.  相似文献   

14.
Hydrogen peroxide, produced by inflammatory and vascular cells, induces oxidative stress that may contribute to endothelial dysfunction. In smooth muscle cells, H2O2 induces production of O2 by activating NADPH oxidase. However, the mechanisms whereby H2O2 induces oxidative stress in endothelial cells are poorly understood. We examined the effects of H2O2 on O2 levels on porcine aortic endothelial cells (PAEC). Treatment with 60 μmol/L H2O2 markedly increased intracellular O2 levels (determined by conversion of dihydroethidium to hydroxyethidium) and produced cytotoxicity (determined by propidium iodide staining) in PAEC. Overexpression of human manganese superoxide dismutase in PAEC reduced O2 levels and attenuated cytotoxicity resulting from treatment with H2O2. L-NAME, an inhibitor of nitric oxide synthase (NOS), and apocynin, an inhibitor of NADPH oxidase, reduced O2 levels in PAEC treated with H2O2, suggesting that both NOS and NADPH oxidase contribute to H2O2-induced O2 in PAEC. Inhibition of NADPH oxidase using apocynin and NOS rescue with L-sepiapterin together reduced O2 levels in PAEC treated with H2O2 to control levels. This suggests interaction-distinct NOS and NADPH oxidase pathways to superoxide. We conclude that H2O2 produces oxidative stress in endothelial cells by increasing intracellular O2 levels through NOS and NADPH oxidase. These findings suggest a complex interaction between H2O2 and oxidant-generating enzymes that may contribute to endothelial dysfunction.  相似文献   

15.
康华靖  李红  权伟  欧阳竹 《植物生态学报》2014,38(10):1110-1116
以C3作物(小麦, Triticum aestivum和大豆, Glycine max)和C4作物(玉米, Zea mays和千穗谷, Amaranthus hypochondriacus)为例, 探讨了其光下暗呼吸速率降低的原因。结果表明, 2% O2条件下, CO2浓度为0时, 叶室CO2浓度维持在0左右, 而胞间CO2浓度(Ci)显著高于叶室CO2浓度。分析认为这是由于此时植物的暗呼吸仍在正常进行。因此, 该测量条件下的表观光合速率应为CO2浓度为0时的光下暗呼吸速率(Rd)。CO2浓度为0时, 不同光强下的Rd均随光强的升高而降低, 且在低光强(50 μmol·m-2·s-1)和高光强(2000 μmol·m-2·s-1)之间存在显著差异, 说明光强对Rd具有较大影响。在2% O2条件下, 经饱和光强充分活化而断光后, 以上4种作物叶片的暗呼吸速率(Rn)均随着时间的推移而下降, 说明光强并未抑制暗呼吸速率。试验结果表明, Rd的降低是由于CO2被重新回收利用所导致, CO2回收利用率随光强的升高而增大, 从低光强(50 μmol·m-2·s-1)到高光强(2000 μmol·m-2·s-1), 小麦、大豆、玉米和千穗谷的回收利用率范围变动分别为22.65%-52.91%、22.40%-55.31%、54.24%-87.59%和72.43%-90.07%。  相似文献   

16.
主要探讨冬枣(Ziziphus jujuba Mill.cv Dongzao)在-1℃的动态气调(CA-Ⅰ,70%O2 0%CO2处理7天,然后转入5%O2 0%CO2中)、普通气调(CA-Ⅱ,5%O2 0%CO2;CA-Ⅲ,10%O2 0%CO2)及普通冷藏和常温(25℃)等条件下,果实发病率、色素、可溶性固形物、可滴定酸、乙醇和乙酸乙酯含量等的变化.结果表明:与普通冷藏相比,气调贮藏能减缓果实的腐烂,抑制色素的分解和减少果肉中乙醇、乙酸乙酯的含量.动态高氧处理能有效地保持果实的颜色,抑制色素降解及果皮褐变.CA-Ⅲ(10%O2 0%CO2)能有效地减少果肉乙醇的含量而CA-Ⅱ(5%O2 0%CO2)能有效地减少果肉乙酸乙酯的含量.气调贮藏的果实可滴定酸及可溶性固形物含量与其他处理的果实没有明显的差异.  相似文献   

17.
Y. Mathieu 《BBA》1969,189(3):422-428
Influence of oxygen on the electron transfers of photosynthesis. II. Influence of very low oxygen concentration on the NADP+ reduction by isolated chloroplasts

The influence of very low O2 concentration on the NADP+ reduction by isolated spinach chloroplasts has been studied.

The results show that in the presence of very low O2 concentration (< 0.3%) NADP+ reduction is partially inhibited. This inhibition may be partially reversed under some conditions, especially when, in spite of the presence of an O2 trap (glucose plus glucose oxidase (EC 1.1.3.4)) an O2 evolution is observed.  相似文献   


18.
Isolated hepatocytes incubated with selenite (30–100 μM) exhibited changes in the glutathione redox system as shown by an increase in O2 consumption, oxidation of glutathione and loss of NADPH. Selenite (50 μM) raised O2 consumption within the 1 h and induced an partial depletion of thiols with a concomitant increase in oxidized glutathione, as well as a decrease in NADPH levels within 2 h. With 100 μM selenite more pronounced effects were obtained such as a total depletion of thiols. This concentration of selenite also lysed cells within 3 h. Arsenite, HgCl2 and KCN prevented the increase in O2 uptake, counteracted loss of thiols and delayed selenite induced lysis. p-Tert-butylbenzoic acid, an inhibitor of gluconeogenesis, decreased selenite dependent O2 consumption and potentiated the effect on NADPH levels as well as the toxic effect. Finally, methionine further enhanced O2 consumption by selenite and also delayed loss of thiols and potentiated selenite toxicity. These results indicated that selenite catalyzed a reduction of O2 in glutathione dependent redox cycles with NADPH as an electron donor. With subtoxic concentrations of selenite (50 μM) there were indications that O2 reduction was terminated by selenite biotransformation to methylated metabolites. With toxic concentrations of selenite (100 μM) it appeared that O2 reduction was eventually limited by the capacity of the cell to regenerate NADPH. It is suggested that a depletion of NADPH mediated the observed cytotoxicity of selenite.  相似文献   

19.
Temperature plays an important role in various aspects of the life history and physiology of ectotherms. We examined the effect of temperature on standard metabolic rate in the mud turtle, Kinosternon subrubrum. We measured O2 consumption and CO2 production at 20°C and 30°C using a flow through respirometery system. Standard metabolic rate was significantly higher at 30°C (9.25 ml O2/h, 6.35 ml CO2/h) compared to 20°C (2.10 ml O2/h, 1.96 ml CO2/h). The Q10 value for O2 was 5.10, and for CO2 was 3.40. Our findings generally agree with those of other studies of metabolism in vertebrate ectotherms.  相似文献   

20.
B.L. Epel  J. Neumann 《BBA》1973,325(3):520-529

1. 1. The mechanism of the photooxidation of ascorbate and of Mn2+ by isolated chloroplasts was reinvestigated.

2. 2. Our results suggest that ascorbate or Mn2+ oxidation is the result of the Photosystem I-mediated production of the radical superoxide, and that neither ascorbate nor Mn2+ compete with water as electron donors to Photosystem II nor affect the rate of electron transport through the two photosystems: The radical superoxide is formed as a result of the autooxidation of the reduced forms of low potential electron acceptors, such as methylviologen, diquat, napthaquinone, or ferredoxin.

3. 3. In the absence of ascorbate or Mn2+ the superoxide formed dismutases either spontaneously or enzymatically producing O2 and H2O2. In the presence of ascorbate or Mn2+, however, the superoxide is reduced to H2O2 with no formation of O2. Consequently, in the absence of reducing compounds, in the reaction H2O to low potential acceptor one O2 (net) is taken up per four electrons transported where as in the presence of ascorbate, Mn2+ or other suitable reductants up to three molecules O2 can be taken up per four electrons transported.

4. 4. This interpretation is supported by the following observations: (a) in a chloroplast-free model system containing NADPH and ferredoxin-NADP reductase, methylviologen can be reduced to a free radical which is autooxidizable in the presence of O2; the addition of ascorbate or Mn2+ to this system results in a two fold stimulation of O2 uptake, with no stimulation of NADPH oxidation. The stimulation of O2 uptake is inhibited by the enzyme superoxide dismutase; (b) the stimulation of light-dependent O2 uptake in the system H2O → methylviologen in chloroplasts is likewise inhibited by the enzyme superoxide dismutase.

5. 5. In Class II chloroplasts in the system H2O → NADP upon the addition of ascorbate or Mn2+ an apparent inhibition of O2 evolution is observed. This is explained by the interaction of these reductants with the superoxide formed by the autooxidation of ferredoxin, a reaction which proceeds simultaneously with the photoreduction of NADP. Such an effect usually does not occur in Class I chloroplasts in which the enzyme superoxide dismutase is presumably more active than in Class II chloroplasts.

6. 6. It is proposed that since in the Photosystem I-mediated reaction from reduced 2,4-dichlorophenolindophenol to such low potential electron acceptor as methylviologen, superoxide is formed and results in the oxidation of the ascorbate present in the system, the ratio ATP/2e in this system (when the rate of electron flow is based on the rate of O2 uptake) should be revised in the upward direction.

Abbreviations: DCMU, 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea; HEPES, hydroxyethyl-piperazineethanesulfonic acid; MES, (N-morpholino)ethanesulfonic acid; DCIP, 2,4-dichlorophenol-indophenol  相似文献   


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